Picosecond gain-switched polymer fiber random lasers

Random lasers are a type of lasers that lack typical resonator structures,offering benefits such as easy integration,low cost,and low spatial coherence.These features make them popular for speckle-free imaging and random number generation.However,due to their high threshold and phase instability,the production of picosecond random lasers has still been a challenge.In this work,we have developed three dyes incorporating polymer optical fibers doped with various scattering nanoparticles to produce short-pulsed random fiber lasers.Notably,stable picosecond random laser emission lasting600 ps is observed at a low pump energy of 50μJ,indicating the gain-switching mechanism.Population inversion and gain undergo an abrupt surge as the intensity of the continuously pumped light nears the threshold level.When the intensity of the continuously pumped light reaches a specific value,the number of inversion populations in the“scattering cavity”surpasses the threshold rapidly.Simulation results based on a model that considers power-dependent gain saturation confirmed the above phenomenon.This research helps expand the understanding of the dynamics behind random medium-stimulated emission in random lasers and opens up possibilities for mode locking in these systems.

On group structures of strategic-form games

There are two recognized classes of strategic-form symmetric games,both of which can be conveniently defined through the corresponding player symmetry groups.We investigate the basic properties of these groups and several related concepts.We generalize the notion of coveringness and adapt their results to characterize these player symmetry groups.We study the relationships between the coveringnesses of various symmetry groups.Our results demonstrate that these symmetry groups have rich mathematical structures that are of game theoretical and economic interests.

运筹学视角下的市场机制设计

市场机制设计是微观经济学的一个前沿领域,其开创者们囊括了2012年和2020年两次诺贝尔经济学奖。市场设计与运筹学从学科关系到发展历史的方方面面都有密切关系,研究问题都既有理论渊源又深受现实问题驱动。本文从运筹学视角简要介绍市场设计的发展现状和趋势,特别介绍次模分析、离散凸分析、算法博弈论等基础方法,并概述市场设计在数字经济和智慧交通领域的潜在应用。最后介绍两个学科领域进一步深度交叉融合所面临的挑战,并给出推动相关科研和教学工作的浅见。

流域土地绿化显著削减了中国河流泥沙含量

Sediment in rivers plays an essential role in the river and watershed ecosystem.Recently,Dethier et al.[1]used an empirical model,which was developed using the data in America and Taiwan Province in China,to estimate suspended sediment concentration(SSC)and generate a long-term record of SSC and sediment fluxes in 414 major rivers worldwide since 1984.The authors concluded that the widespread decreases in river sediment fluxes in the North Hemisphere(NH)resulted from the dams,while the increases in river sediment fluxes in the South Hemisphere were possibly related to changes in land use.Regardless of the discussion on whether such an empirical model could be extrapolated to the global rivers for accurately retrieving SSC from Landsat imagery,the elucidation of the continuous declines in SSC in the NH rivers since1980s was incomplete.As Dethier et al.[1]demonstrated,the spatial and temporal variations in river sediment were regulated by climate change and human activities[2],including precipitation,land cover and land use,damming,and dredging activities[3-6].

Construction of a bacterial artificial chromosome library of S-type CMS maize mitochondria

In order to isolate mitochondrial genes easily, we have developed a new method to construct S-type CMS maize mitochondrial gene library by means of embedding mitochondria and enzymatic digesting mitochondria in situ, preparing mtDNA by electrophoresis, digesting LMP agarose with β-agarase, using BAC vector and electroporation. About 2 500 white clones of Mo17 CMS-J mitochondrial gene library were obtained with the average size of 18.24 kb, ranging from 5 to 40 kb, 63.6% inserts came from mitochondrial genome and represented 48 × mitochondrial genome equivalents. All the probes had detected the positive clones in the gene library. It is helpful to elucidating the maize mitochondrial genome structure and mechanism of S-type CMS, and may give some valuable reference to the construction of other plant mitochondrial genome library.

SCHEDULING WITH REJECTION AND NON-IDENTICAL JOB ARRIVALS

In this paper, we address the scheduling problem with rejection and non-identical job arrivals, in which we may choose not to process certain jobs and each rejected job incurs a penalty, Our goal is to minimize the sum of the total penalties of the rejected jobs and the maximum completion time of the processed ones, For the off-line variant, we prove its NP-hardness and present a PTAS, and for the on-line special case with two job arrivals, we design a best possible algorithm with competitive ratio （√5＋1/2） .

APPROXIMATION SCHEMES FOR SCHEDULING A BATCHING MACHINE WITH NONIDENTICAL JOB SIZE

In this paper we study the problem of scheduling a batching machine with nonidentical job sizes. The jobs arrive simultaneously and have unit processing time. The goal is to minimize the total completion times. Having shown that the problem is NP-hard, we put forward three approximation schemes with worst case ratio 4, 2, and 3/2, respectively.

最小支撑树博弈:重新审视Bird配置

最小支撑树博弈是合作博弈中的经典模型,自1973年被Claus和Kleitman提出后持续得到学术界关注.最小支撑树博弈不仅跟图论和组合优化中的最小支撑树问题一脉相承,还在水网、电网和公路铁路网建设中的成本分摊问题中有重要应用. Bird配置因其简洁性和直观性持续受到大量关注,是最小支撑树博弈最著名的求解方案.本文基于Edmonds对最小支撑树问题的线性规划表示,利用对偶定理给出Bird配置一种新的等价公式.本文还研究了最小支撑树博弈的一种推广,即点加权的最小支撑树博弈,并证明了Bird配置的一个变形依然在这个推广博弈的核中.

Location-aware downlink and uplink power control and throughput optimization in cellular cognitive radio networks

In this paper,we consider throughput maximization in cognitive radio systems with proper power control.In particular,we incorporate location-awareness into the power control design and maximize the average throughput of the cognitive system.As we shall show,the proposed approach effectively utilizes the“spatial opportunity”to maximize the system throughput,which clearly outperforms traditional power control methods.Further,the proposed approach still exhibits significant throughput gain even considering imperfect position information,with appropriate robust design modifications.

An efficient cooperative sensing scheme with bandwidth-limited control channel

The conflict between scarcity of spectrum resources and low spectrum utilization motivates the concept of cognitive radio,which allows secondary unlicensed users to borrow temporally unused spectrum bands from primary licensed users.Spectrum sensing is one of the key functionalities that enable spectrum hole discovery and interference avoidance.As single user spectrum sensing may experience performance degradation in harsh wireless environment due to fading and shadowing,user cooperation is introduced to exploit spatial diversity for better sensing performance.However,local sensing results must be transmitted via a control channel.The advantage of cooperative sensing can be compromised by bandwidth limitation of the control channel.To overcome this,a benching cooperative sensing scheme is proposed in this paper.This scheme can reduce time overhead of sensing information exchange under a communication constraint.Analytical results of periodic sensing efficiency are then deduced while sensing parameters are optimized.Based on these,a recursive sensing algorithm exploiting prior channel state information is developed.Numerical results are presented to demonstrate the potential of our scheme.