A compromised large-scale neighborhood search heuristic for capacitated air cargo loading planning

Cost effectiveness is central to the air freight forwarders. In this work, we study how an air freight forwarder should plan its cargo loading in order to minimize the total freight cost given a limited number of rented containers. To solve the problem efficiently for practical implementation, we propose a new large-scale neighborhood search heuristic. The proposed large-scale neighborhood relaxes the subset-disjoint restriction made in the existing literature; the relaxation risks a possibility of infeasible exchanges while at the same time it avoids the potentially large amount of checking effort required to enforce the subset-disjoint restriction. An efficient procedure is then used to search for improvement in the neighborhood. We have also proposed a subproblem to address the difficulties caused by the fixed charges. The compromised large-scale neighborhood (CLSN) search heuristic has shown stably superior performance when compared with the traditional large-scale neighborhood search and the mixed integer programming model.     

大型滑坡发生的时间分布与固体潮的关系

为研究大型滑坡在发生时间呈现的规律,本文对我国近年来发生的大型滑坡在时间分布和诱导因素上进行了统计。从统计结果可以看出,自然边坡往往在一定的诱导因素下发生失稳破坏,而大型滑坡的失稳破坏在时间分布上则表现出望日或者朔日前后易于发生,并且滑坡在一天中发生的具体时刻则呈现出正态分布的特点。因此,根据固体潮的理论,以及固体潮在一天之中引潮力的变化与滑坡发生时刻的对应关系,本文认为固体潮是诱导大型边坡失稳的因素之一。同时由于组成边坡物质的蠕变特性不同,造成了大型滑坡的发生往往有超前或滞后现象,以上结果为滑坡的预报或预防工作提供了一定的理论支持。     

The cross-entropy method with patching for rare-event simulation of large Markov chains

There are various importance sampling schemes to estimate rare event probabilities in Markovian systems such as Markovian reliability models and Jackson networks. In this work, we present a general state-dependent importance sampling method which partitions the state space and applies the cross-entropy method to each partition. We investigate two versions of our algorithm and apply them to several examples of reliability and queueing models. In all these examples we compare our method with other importance sampling schemes. The performance of the importance sampling schemes is measured by the relative error of the estimator and by the efficiency of the algorithm. The results from experiments show considerable improvements both in running time of the algorithm and the variance of the estimator.     

基于扫频采样的飞秒激光大尺寸测距方法研究

作为一种高精度测量工具,飞秒激光具有优于传统激光技术的特性,已被广泛应用于工业生产、航空航天、科学研究等领域。扫频采样法在很大程度上改善了机械振动、扫描速度过慢等问题,对飞秒激光的绝对测距性能提升有着重要的意义。基于扫频采样原理,提出了一种利用飞秒激光的大尺寸距离测量方法,并对该技术的测量原理、干涉光谱和解调算法等方面进行了研究。首先,根据飞秒激光的锁模生成原理和压电陶瓷的压电效应,介绍了飞秒激光器连续扫描重复频率的方法。在此基础上,结合传统的光学采样法原理,解释了扫频采样法的测距原理,推导并讨论了光纤延迟线的长度对扫描距离的影响。然后,搭建了基于扫频采样的飞秒激光测距系统,在线性导轨上进行了远距离的测量实验,同时设计了基于迈克尔逊干涉原理的He-Ne激光参考光路。根据实验环境修正了空气群折射率,分析了测量距离对光谱条纹峰值和宽度的影响,测量了不同目标位置处的激光扫描距离。在50.4 m的测量范围内,扫描距离从0.56 mm增加到1.12 mm,充分验证了光纤延迟线对提升大尺寸测距能力的重要性。周期性的频率扫描可产生互相关条纹,通过对测量光谱条纹进行希尔伯特变换处理,解算出实时的频率变化量和采样倍乘系数,从而获取被测的距离信息。此外,为了减小系统的时间延迟误差,提高测量的准确性,采用差分原理对算法进行了改进。在希尔伯特算法基础上,分别对频率和距离进行差分处理,解算距离信息。实验结果表明,经过对比,采用基于距离差分的改进算法处理数据,性能结果较好。算法改进后,系统在50 m范围内的测量精度从11 μm提高到4 μm,相对精度从2.2×10-9提高到8×10-8,测距准确性明显提高。通过分析重复性测量数据,并与增量式激光干涉仪结果比对,测量误差的标准差从10 μm提高到2 μm,最大相对稳定性从2×10-9提高到4×10-8,测距稳定性明显提高。因此,该方法有较为优秀的大尺寸测距能力,具有同时实现高精度、大尺寸、快速绝对测距的潜力,在未来的精密光谱测量领域有着很大的前景。     

Cosmological Applications of a Geometrical Interpretation of “c”

We make the hypothesis that the velocity of light and the expansion of the universe are two aspects of one single concept connecting space and time in the expanding universe. We show that solving Friedman’s equations with that interpretation (keeping c = constant) could explain number of unnatural features of the standard cosmology. We thus examine in that light the flatness problem, the problem of the observed uniformity in term of temperature and density of the cosmological background radiation and the small-scale inhomogeneity problem. We finally show that using this interpretation of c leads to reconsider the Hubble diagram of distance moduli and redshifts as obtained from recent observations of type Ia supernovae without having to need an accelerating universe.     

Interpretation of simple and cloud-resolving simulations of moist convection–radiation interaction with a mock-Walker circulation

An idealized two-dimensional mock-Walker circulation in the tropical atmosphere forced by prescribed horizontal gradients in sea-surface temperature (SST) is discussed. This model problem includes feedbacks between cumulus convection and tropical large-scale circulations that have proved challenging for global climate models to predict accurately. Three-dimensional cloud-resolving model (CRM) simulations that explicitly simulate turbulent circulations within individual cloud systems across 4,096 and 1,024 km-wide Walker circulations are compared with a simple theoretical model, the Simplified Quasiequilibrium Tropical Circulation Model (SQTCM). This theoretical model combines the weak-temperature-gradient approximation with a unimodal truncation of tropospheric vertical structure coupled to highly simplified formulations of moist precipitating cumulus convection and its cloud-radiative feedbacks. The rainfall, cloud and humidity distribution, circulation strength, energy fluxes and scaling properties are compared between the models. The CRM-simulated horizontal distribution of rainfall and energy fluxes are adequately predicted by the SQTCM. However, the humidity distribution (drier subsidence regions and high-humidity boundary layers in the CRM), vertical structure and domain-size scaling of the circulation differ significantly between the models. For the SQTCM, the concept of gross moist stability – related to advection of moist static energy (MSE) out of tropospheric columns by the mean divergent circulation – is used to explain the width and intensity of the rainy region. Column MSE budgets averaged across the ascent branch of the simulated Walker circulation provide similar insight into the cloud-resolving simulations after consideration of the more complex horizontal and vertical circulation structure and the role of transient eddies. A nondimensional ascent-region moist stability ratio α, analogous to the SQTCM gross moist stability, is developed. One term of α is related to the vertical profiles of ascent-region mean vertical motion and ascent-region edge MSE; a second term is proportional to eddy export from the ascent region. Smaller α induces a narrower, rainier ascent region. The sensitivity of the SQTCM and CRM to a uniform 2 K increase in SST is compared, and the rainy upward branch of the circulation narrows in both models. MSE budget arguments are used to explain this behavior. In the simple model, the gross moist stability is a decreasing function of tropospheric temperature. Hence gross moist stability reduces and the ascent region narrows as the SST increases. In the CRM, increased atmospheric radiative cooling due to the warmer and moister troposphere destabilizes the MSE profile and decreases α, inducing a narrower ascent region. In the CRM, and to a lesser extent in the SQTCM, intensified shortwave cloud forcing in the warmer climate causes a negative radiative feedback on the SST change.Funding for this work from NSF grant DMS-0139794 is gratefully appreciated     

Decentralized Stabilizing State Feedback Controllers for a Class of Large-Scale Systems Including State Delays in the Interconnections

The problem of the decentralized stabilization of a class of large-scale nonlinear and linear systems including time-varying delays in the interconnections is considered. By combining the Razumikhin-type theorem with the Lyapunov stability theory, we propose a class of decentralized state feedback controllers which can guarantee always some type of stability of large-scale time-delay systems. In this paper, we assume that the time-varying delays are continuous and bounded nonnegative functions. Furthermore, since the proposed decentralized state feedback controllers are independent of the delays, the results obtained in this paper are applicable to systems without exact knowledge of the delays, i.e., systems with perturbed delays. Finally, a numerical example is given to demonstrate the validity of the results.     

Investigation on lateral dispersion characteristics of fuel particles in dense phase zone of a large-scale circulating fluidized bed boiler under combustion conditions

The dispersion characteristics of fuel particles in the dense phase zone in circulating fluidized bed (CFB) boilers have an important influence on bed temperature distribution and pollutant emissions. However, previous research in literature was mostly on small-scale apparatus, whose results could not be applied directly to large-scale CFB with multiple dispersion sources. To help solve this problem, we proposed a novel method to estimate the lateral dispersion coefficient (D_x) of fuel particles under partial coal cut-off condition in a 350 MW supercritical CFB boiler based on combustion and dispersion models. Meanwhile, we carried out experiments to obtain the D_x in the range of 0.1218–0.1406 m²/s. Numerical simulations were performed and the influence of operating conditions and furnace structure on fuel dispersion characteristics was investigated, the simulation value of D_x was validated against experimental data. Results revealed that the distribution of bed temperature caused by the fuel dispersion was mainly formed by char combustion. Because of the presence of intermediate water-cooled partition wall, the mixing and dispersion of fuel and bed material particles between the left and right sides of the furnace were hindered, increasing the non-uniformity of the bed temperature near furnace front wall.