Encroachment drives facilitation at alpine shrublines

Ongoing encroachment is driving recent alpine shrubline dynamics globally,but the role of shrub-shrub interactions in shaping shrublines and their relationships with stem density changes remain poorly understood.Here,the size and age of shrubs from 26 Salix shrubline populations along a 900-km latitudinal gradient(30°-38°N)were measured and mapped across the eastern Tibetan Plateau.Point pattern analyses were used to quantify the spatial distribution patterns of juveniles and adults,and to assess spatial associations between them.Mean intensity of univariate and bivariate spatial patterns was related to biotic and abiotic variables.Bivariate mark correlation functions with a quantitative mark(shrub height,basal stem diameter,crown width)were also employed to investigate the spatial relationships between shrub traits of juveniles and adults.Structural equation models were used to explore the relationships among conspecific interactions,patterns,shrub traits and recruitment dynamics under climate change.Most shrublines showed clustered patterns,suggesting the existence of conspecific facilitation.Clustered patterns of juveniles and conspecific interactions(potentially facilitation)tended to intensify with increasing soil moisture stress.Summer warming before 2010 triggered positive effects on population interactions and spatial patterns via increased shrub recruitment.However,summer warming after2010 triggered negative effects on interactions through reduced shrub recruitment.Therefore,shrub recruitment shifts under rapid climate change could impact spatial patterns,alter conspecific interactions and modify the direction and degree of shrublines responses to climate.These changes would have profound implications for the stability of alpine woody ecosystems.

Effect of autaptic delay signal on spike-timing precision of single neuron

Experimental and theoretical studies have reported that the precise firing of neurons is crucial for sensory representation.Autapse serves as a special synapse connecting neuron and itself,which has also been found to improve the accuracy of neuronal response.In current work,the effect of autaptic delay signal on the spike-timing precision is investigated on a single autaptic Hodgkin–Huxley neuron in the present of noise.The simulation results show that both excitatory and inhibitory autaptic signals can effectively adjust the precise spike time of neurons with noise by choosing the appropriate coupling strength g and time delay of autaptic signalτ.The g–τparameter space is divided into two regions:one is the region where the spike-timing precision is effectively regulated;the other is the region where the neuronal firing is almost not regulated.For the excitatory and inhibitory autapse,the range of parameters causing the accuracy of neuronal firing is different.Moreover,it is also found that the mechanisms of the spike-timing precision regulation are different for the two kinds of autaptic signals.

Multi-Bit Sliding Stack Decoding Algorithm for OVXDM

Overlapped x domain multiplexing(OVXDM) is a promising encoding technique to obtain high spectral efficiency by utilizing inter-symbol interference(ISI) intelligently. However, the computational complexity of maximum likelihood sequence detection(MLSD) increases exponentially with the growth of spectral efficiency in OVXDM, which is unbearable for practical implementations. In this paper, based on a novel path metric associating adjacent symbols, we propose a multi-bit sliding stack decoding(Multi-Bit SSD) algorithm to achieve multiple-bit decoding simultaneously in OVXDM. Theoretical analysis is provided for the algorithm, which indicates the relationship between the performance and parameters including multiplexing waveform, overlapping fold and sliding window size. Simulation results show that the proposed algorithm can achieve better decoding performance and higher spectral efficiency than conventional fast decoding algorithms.

耐高温阻燃聚苯腈树脂的制备及性能

利用间苯二酚、双酚A和联苯二酚分别与4-硝基邻苯二甲腈发生亲核取代反应合成了3种耐高温苯腈单体,并利用4-氨基苯氧邻苯二甲腈为催化剂制备了3种聚苯腈树脂。采用红外光谱、核磁氢谱、差示扫描量热、热重分析、动态力学分析、扫描电镜、导热系数仪和X射线衍射分析表征了苯腈单体和半本征型聚苯腈树脂的结构与性能。结果表明,3种苯腈单体的熔点在180~226℃,加工温度窗口为40~75℃。所制备3种聚苯腈树脂的起始分解温度(Td5%)高于480℃,玻璃化转变温度高于335℃,极限氧指数(LOI)高于57,导热系数大于0.21 W/(m·K),表现出良好的加工性、优异的热稳定性、突出的阻燃性和良好的导热性能。

Bidirectional Viterbi Decoding Algorithm for OvTDM

Overlapped time domain multiplexing(OvTDM)is an innovative encoding scheme that can obtain high spectral efficiency.However,the intentional inter-symbol interference(ISI)caused by OvTDM will make the decoding process more complex.The computational complexity of maximum likelihood sequence detection increases exponentially with the growth of spectral efficiency in OvTDM.As a consequence of high complexity,the decoding effort for a given spectral efficiency may occasionally exceed the physical limitations of the decoder,leading inevitably to buffer overflows and information erasures.In this paper,we propose a bidirectional Viterbi algorithm(BVA)based on the bidirectional sequence decoding for OvTDM.With the BVA,the decoding operation starts simultaneously from the both ends of the corresponding trellis and stops at the middle of trellis.The simulation results show that compared with Viterbi algorithm(VA),the decoding time of BVA can be reduced by about half.And the memory space of two decoders in BVA are about half of that in VA,which means that the BVA has lower memory requirements for decoder.And the decoding performance of BVA is almost the same as VA.

Difference between grid connections of large-scale wind power and conventional synchronous generation

In China, regions with abundant wind energy resources are generally located at the end of power grids. The power grid architecture in these regions is typically not sufficiently strong, and the energy structure is relatively simple. Thus, connecting large-capacity wind power units complicates the peak load regulation and stable operation of the power grids in these regions. Most wind turbines use power electronic converter technology, which affects the safety and stability of the power grid differently compared with conventional synchronous generators. Furthermore, fluctuations in wind power cause fluctuations in the output of wind farms, making it difficult to create and implement suitable power generation plans for wind farms. The generation technology and grid connection scheme for wind power and conventional thermal power generation differ considerably. Moreover, the active and reactive power control abilities of wind turbines are weaker than those of thermal power units, necessitating additional equipment to control wind turbines. Hence, to address the aforementioned issues with large-scale wind power generation, this study analyzes the differences between the grid connection and collection strategies for wind power bases and thermal power plants. Based on this analysis, the differences in the power control modes of wind power and thermal power are further investigated. Finally, the stability of different control modes is analyzed through simulation. The findings can be beneficial for the planning and development of large-scale wind power generation farms.

Growth response of Abies spectabilis to climate along an elevation gradient of the Manang valley in the central Himalayas

The Himalayas are characterized by a broad gradient of bioclimatic zones along their elevation.However,less is known how forest growth responds to climatic change along elevation.In this study,four standard treering width chronologies of Himalayan fir(Abies spectabilis)were developed,spanning 142–649 years along an elevation gradient of 3076–3900 m a.s.l.Principal component analysis classified the four chronologies into two groups;the ones at lower elevations(M1 and M2)and higher elevations(M3 and M4)show two distinct growth trends.Radial growth is limited by summer(June–August)precipitation at M3,and by precipitation during spring(March–May)and summer at M4.It is limited by spring temperatures and winter precipitation(December–February)at M1.Tree-ring width chronologies also significantly correlate with winter and spring Palmer Drought Severity Index(PDSI)at M1,and with summer PDSI at M3 and M4.Thus,Himalayan fir growth at high elevations is mainly limited by moisture stress rather than by low temperatures.Furthermore,the occurrence of missing rings coincides with dry periods,providing additional evidence for moisture limitation of Himalayan fir growth.

A Decoding Method Based on RNN for OvTDM

Overlapped X domain multiplexing(Ov XDM) is a promising encoding technique to obtain high spectral efficiency by utilizing Inter-Symbol Interference(ISI). However, the computational complexity of Maximum Likelihood Sequence Detection(MLSD) increases exponentially with the growth of spectral efficiency in Ov XDM, which is unbearable for practical implementations. This paper proposes an Ov TDM decoding method based on Recurrent Neural Network(RNN) to realize fast decoding of Ov TDM system, which has lower decoding complexity than the traditional fast decoding method. The paper derives the mathematical model of the Ov TDM decoder based on RNN and constructs the decoder model. And we compare the performance of the proposed decoding method with the MLSD algorithm and the Fano algorithm. It’s verified that the proposed decoding method exhibits a higher performance than the traditional fast decoding algorithm, especially for the scenarios of a high overlapped multiplexing coefficient.

Multi-dimensional and complicated electromagnetic interference hardware-in-the-loop simulation method

A typical electronic communication system, such as GPS receiver, unmanned aerial vehicle＇s （UAV＇s） data link, and radar, faces multi-dimensional and complicated electromagnetic interference in operating environment. To measure the anti- interference performance of the electronic communication system in the complicated electromagnetic interference environment, a method of multi-dimensional and complicated electromagnetic interference hardware-in-the-loop simulation in an anechoic room is proposed. It takes into account the characteristics of interference signals and the positional relationship among interference, the receiver and the transmitter of the electronic communication system. It uses the grey relational method and the angular domain mapping error correction method to control the relevant parameters, the microwave switch and so on, thus achieving the approximately actual mapping of the outdoor multi-dimensional and complicated electromagnetic interference in the anechoic room. To verify the effectiveness of this method, the multi-dimensional and complicated electromagnetic interference of the UAV＇s data link is simulated as an example. The results show that the degree of correlation between the calculated signal to interference ratio of the data link receiver in the actual scene and the measured signal to interference ratio of the data link receiver simulated with this method in the anechoic room is 0.968 1, proving that the method is effective for simulating the complicated electromagnetic interference.

含磷丙烯酸酯核壳阻燃剂的合成及在聚乳酸中的应用

为了同时改善聚乳酸(PLA)的阻燃性和韧性,文中以甲基膦酸二乙酯丙烯酸酯(DEAMP)为核层材料、甲基丙烯酸甲酯(MMA)为壳层材料、三烯丙基异氰酸酯(TAIC)为核层交联剂,通过种子乳液聚合法,制备了平均粒径约190 nm的含磷丙烯酸酯核壳阻燃剂(P-CM)。透射电镜图片显示了典型的核壳结构;差示扫描量热分析和热重分析结果表明,P-CM核层、壳层的玻璃化转变温度分别为-13.6℃和115.6℃、初始分解温度(Td5%)为263℃、分解后残余物为36%。将5%P-CM用于增韧和协效10%APP/5%β-CD阻燃的PLA,结果表明,与10%APP/10%β-CD阻燃的PLA比,极限氧指数(LOI)提高了5.7%;冲击强度提高了182.5%,拉伸强度提高了2.9%,断裂伸长率增加了28.9%,获得了具有高阻燃性和高韧性的PLA材料。

Resource Allocation Method of Device-to-Device Communication

In this paper, we study D2D (Device-to-Device) communication underlying LTE-Advanced uplink system. Since D2D communication reuses uplink resources with cellular communication in this scenario, it’s hard to avoid the inference between D2D users and cellular users. If there is no restriction for D2D communication on using the whole uplink frequency band, it will have a strong negative impact on cellular communication. In order to overcome this shortage, we propose a resource allocation method that D2D users and cellular users use orthogonal frequency resources. This method will effectively reduce the inference between both kinds of communication. However, an obvious disadvantage of this method is no effective use of uplink resources. Based on this, we propose an optimized resource allocation method that a specific cellular user will be chosen to reuse the RBs (Resource Block) of D2D users. These ideas will be taken into system-level simulation, and from the results of simulation we can see that the optimized method has the ability to improve overall system performance and limit inference for cell-edge users.

变频器主从控制技术在双传动提升机上的应用

水泥厂双传动提升机普遍采用软启动方式控制,该方式仅仅实现单设备的启动与故障保护功能,无法实现设备的性能保护,最重要的是软启动方式无法实现主从电机间的"智慧交流",运行过程中主从电机间的同步性不能保证,也就无法实现设备的长期稳定可靠运行。从设备性能优化、保证主从设备同步性角度出发,将变频器主从控制技术应用在关键岗位提升机上,不仅能保证电机具有良好的启动和运行性能,更能实现主从电机间的负载均衡和运行同步,大大降低不平衡与不同步导致的电机电流偏差大以及可能产生的设备损坏,甚至是事故的发生,从而保证水泥厂生产的高效稳定运行。

Bidirectional Viterbi Decoding Algorithm for OvTDM

Overlapped time domain multiplexing(OvTDM)is an innovative encoding scheme that can obtain high spectral efficiency.However,the intentional inter-symbol interference(ISI)caused by OvTDM will make the decoding process more complex.The computational complexity of maximum likelihood sequence detection increases exponentially with the growth of spectral efficiency in OvTDM.As a consequence of high complexity,the decoding effort for a given spectral efficiency may occasionally exceed the physical limitations of the decoder,leading inevitably to buffer overflows and information erasures.In this paper,we propose a bidirectional Viterbi algorithm(BVA)based on the bidirectional sequence decoding for OvTDM.With the BVA,the decoding operation starts simultaneously from the both ends of the corresponding trellis and stops at the middle of trellis.The simulation results show that compared with Viterbi algorithm(VA),the decoding time of BVA can be reduced by about half.And the memory space of two decoders in BVA are about half of that in VA,which means that the BVA has lower memory requirements for decoder.And the decoding performance of BVA is almost the same as VA.

Sidelobe Suppression in CR-OFDM system by Adding Extended Data Carriers

Out-band radiation is a severe problem for Cognitive Radio with OFDM system (CR-OFDM) which is caused by the sidelobe of OFDM signals. Lots of studies have been done on suppressing the sidelobe power and numerous methods have been proposed. In this paper, we propose a novel method to minimize the sidelobe by adding extended data carrier so called EDC to the original data carriers so as to protect primary user (PU) spectrum. Unlike the methods before, the EDCs are deployed within the secondary user (SU) data frequency spectrum to fully use the spectrum. Moreover, we derive the linear least squares problem to get the optimal weighting factors of EDCs to minimize the sidelobe power which is subject to an original data interference constraint. By simulation, we find that EDC is more capable in sidelobe suppression than method of Cancellation Carrier (CC) while EDC has only a small loss in BER performance.

Analysis of Relay Deployment Based on Handover Outage Probability in High Speed Scenarios

The LTE and LTE-Advanced systems are supposed to be the most popular cellular network in 4Gnetworks. Relay technology is one of the most preferred technologies proposed in LTE-Advanced standardization to improve the capacity and coverage. This paper analyses the handover outage probability through relay deployment, and proposes some proofs and suggestions for relay deployment to minimize the handover outage probability in high speed scenarios.

Performance of HARQ in Device-to-Device Communication

In this paper, we study D2D (Device-to-Device) communication underlying LTE-Advanced uplink system. Since D2D communication reuses uplink resources with cellular communication in this scenario, it’s hard for D2D users to avoid the interference from cellular users while cellular users are communication with eNB (evolved Node B). HARQ (Hybrid Automatic Repeat reQuest) is widely used in LTE-Advanced system in order to improve the accurate rate of cellular communication. Hence, we consider studying the integration of D2D with HARQ, so as to achieve the purpose of improving the throughput of D2D communication and the performance of overall system. Synchronous HARQ is considered to introduce into D2D communication procedures. What’s more, this idea will be taken into system-level simulation. From the simulation results, we can see that the throughput of D2D communication gets a lot of gain and the performance of overall system is improved as well. In addition, Synchronous HARQ technique can significantly decrease the BLER (Block Error Rate) of D2D communication, especially for which in a bad channel condition.

The current and future of terrestrial carbon balance over the Tibetan Plateau

The contemporary carbon balance over the Tibetan Plateau is highly uncertain with a ten-fold difference between various estimates.In a warming world,the potential exists for a large carbon release from its permafrost which could compromise China’s 2060 carbon-neutral goal.Here,we used a satellite-and inventory-based approach,ecosystem models,and atmospheric inversions to estimate that the carbon sink was 33.12–37.84 TgC yr^(–1)during 2000–2015.The carbon sink induced by climate change and increasing CO_(2) levels largely overcompensated for a livestock grazing-induced carbon source of 0.38TgC yr^(-1).By 2060,the carbon sink is projected to increase by 38.3–74.5% under moderate to high emissions scenarios,with the enhanced vegetation carbon uptake outweighing the warming-induced permafrost carbon release.The restoration of degraded grassland could sequestrate an additional 9.06 TgC yr^(-1),leading to a total carbon sink of 57.78–70.52 TgC yr^(-1).We conclude that the Tibetan Plateau’s ecosystems absorbed two-and-a-half times the amount of its cumulative fossil CO_(2) emissions during 2000–2015 and that their carbon sinks will almost double in strength in the future,helping to achieve China’s pledge to become carbon neutral by 2060.

Unmanned aerial vehicle strike on a flat plate:Tests and numerical simulations

The incursion of Unmanned Aerial Vehicles(UAVs)into airports often occurs due to the popularity of drones,which may lead to a threat to aircraft flight safety.Therefore,estimating the dynamic impact load caused by drone strikes is essential.This paper proposes a test method with high precision and low cost involving launching of a UAV to impact a flat plate specimen by using an air gun.The test results of UAVs impacting flat plates at different impact velocities,such as the UAV dam-age deformation captured by a high-speed camera and strain vs time dynamic response curves of plates,were obtained and analysed.At the same time,a corresponding numerical simulation was car-ried out by using the explicit finite element software LS-DYNA.The predicted damage to the UAV and strain on the flat plate during the strike process were compared with the test results.The overall trend of the simulation results is in good agreement with the test results,at least for the first three mil-liseconds of the event.This shows that the numerical simulation model established in this paper is rea-sonable.The UAV numerical method established in the present paper can be used to carry out numerical simulations and evaluations of the collision safety of UAVs against large aircraft and high-value ground targets.The results show that the local deformation of the impacted target is uneven due to the distribution of concentrated mass components such as motors,battery,and camera.As the impact velocity of the UAV increases,all parts of the UAV are seriously damaged and basically in a fragmented state,and the battery is greatly deformed.The interaction between the UAV and the flat plate specimen is approximately 2.7 ms,and the UAV numerical simulation model established in this paper can well simulate the real UAV impact process.

有限度的人类活动促进野生动物融入城市生态系统

Human-wildlife interactions shape human cultures,animal communities,and species evolution[1].It can generate a range of positive values,including important habitats for wildlife,recreation,and scientific and ecological values for humans,which are beneficial for wildlife conservation and the promotion of human well-being[2].Nevertheless,human-wildlife interactions are often negative.Conflicts between humans and wildlife have existed ever since humans first colonized the Earth and began sharing its landscapes and resources with wildlife.In particular,more significant conflicts have arisen as growing populations and increased resource demand have led to habitat degradation,which has further triggered the extinction and decline of numerous species,economic losses,and uncountable human deaths[3,4].

藏东南亚高山暗针叶林干扰迹地森林更新调查

藏东南为我国主要天然林区,是全球生物多样性最丰富的地区之一,同时也是我国重要的生态安全屏障.在实施国家天然林保护工程之前,该地区天然林曾受到干扰(采伐、林火)的影响.为了探究亚高山暗针叶林采伐和火烧迹地上森林更新的过程,本研究选取藏东南色季拉山急尖长苞冷杉(Abies georgei var. smithii)采伐迹地和火烧迹地,设置了8块森林样地(30 m×30 m),采集树轮样本并进行样地调查.通过对干扰迹地边缘区树轮序列的生长释放分析,推测采伐活动发生在1991年左右,火烧迹地形成于1942年左右.样地调查揭示,干扰迹地内树种更新密度为222~589株/hm^2.过去30~70年来,西北坡向采伐迹地上的更新以急尖长苞冷杉为主,而西南坡火烧迹地的原生林则主要被川滇高山栎(Quercus aquifolides)、高山柏(Sabina squamata)和林芝云杉(Picea likiangensis var. linzhiensis)次生林所取代.因此,今后的研究亟待监测干扰迹地内的微环境状况,以期为变暖背景下藏东南森林保护和管理提供科学依据.