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Search Results: 1 - 10 of 207610 matches for " HUANG Cong-De "
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Carbon density, storage and distribution in birch forest ecosystem on the forestland converted from farmland

WU Xiao-shan,HUANG Cong-de,

生态学杂志 , 2007,
Abstract: 对退耕还林5年生的桦木林生物量、碳素密度、碳贮量及其空间分布进行测定。结果表明,桦木各器官的碳素密度在0.4519~0.5137gC.g-1,排列顺序为枝>干>叶>根颈>粗根>中根>细根;死地被物层的碳素含量为0.3953gC.g-1,土壤平均碳素密度为0.0150gC.g-1,随土层深度的增加,各层次土壤碳素密度呈逐渐减少的趋势;桦木林生态系统总的碳贮量为127.9298tC.hm-2,其中乔木层为21.9282tC.hm-2,占整个生态系统的17.14%,死地被物为0.3401tC.hm-2,占0.27%,林地土壤(0~60cm)为105.6615tC.hm-2,占82.59%;桦木各器官的碳贮量与其生物量成正比例的关系,树干的生物量最大,其碳贮量也最大,占乔木层碳贮量的57.33%;5年生桦木林年净生产力为8.9912t.hm-2.a-1,有机碳年固定量为4.4537tC.hm-2.a-1。较之退耕前,桦木林生态系统碳贮量增加15.4797t.hm-2。
Spatiotemporal variation of carbon storage in forest vegetation in Sichuan Province

HUANG Cong-de,ZHANG Jian,YANG Wan-qin,TANG Xiao,

应用生态学报 , 2007,
Abstract: Based on the modeling of forest biomass and timber volume and the 1974-2004 forest inventory data, the spatiotemporal variation of carbon density and storage in forest vegetation in Sichuan Province was studied. The results showed that the forest carbon storage was increased from 300.02 Tg in 1974 to 469.96 Tg in 2004, with an annual increment of 1.51%, which suggested that the forests in Sichuan Province were the sink of CO2. However, owing to the increase of plantations, the average carbon density of forest vegetation decreased from 49.91 Mg x hm(-2) to 37.39 Mg x Shm(-2), implying that Sichuan forests had a great potential of carbon sequestration through artificial forest management. The carbon storage in Sichuan forests had a spatial heterogeneity, and the ranked order was northwest alpine gorge area > southwest mountainous area > low-mountain area > hilly area > western plain. Forest carbon density increased from southwest area to northwest area, with the order of hilly area < northern plain < southwest mountain area < low-mountain area < northwest alpine gorge area. It was suggested that forest management according to different sub-regions would improve the potential of carbon sequestration in Sichuan forests.
Dynamics on forest carbon stock in Sichuan Province and Chongqing City

HUANG Cong-De,ZHANG Jian,YANG Wan-Qin,TANG Xiao,ZHAO An-Jiu,

生态学报 , 2008,
Abstract: Forest in Sichuan (including Chongqing) locate in the eastern of Tibet Plateau honored by the third pole in the world. As a principal part of SW forest region, the second largest forest region in China, the forest carbon stock plays an important role in global carbon cycle, implying that it is important for forest carbon stock evaluation to understand the role of the forest in mitigating climate change. Therefore, carbon stocks in Sichuan (including Chongqing) forest at different phases were evaluated to understand the contribution of Sichuan forest to mitigate climate change, employing the methods of establishing the model of forest biomass and volume, measuring carbon content in different stands and integrating four provincial forest inventory data in Sichuan (including Chongqing). Mean carbon content of the studied forest stands was 51.09%, ranging from 46.75% to 54.89% ,and depending on the forest stands. On average, carbon content was 52.82% in the coniferous forest, which was significantly higher than that in the broadleaved forest (49.37%). Forest carbon stock in Sichuan increased 140.53 Tg C from 383.04 TgC in 1998 to 523.57 TgC in 2003 and by 2.11% annually during the study period, which was more 0.22% than that of the mean increment in China, implying that Sichuan (including Chongqing) forest is carbon sink in atmospheric carbon dioxide, and contributes to climate change mitigation. Correspondingly, average carbon density in the forest was 38.93, 38.68, 39.17 MgC/hm2, and 41.66 MgC/hm2, respectively, and showed the increasing trend during the period of four forestry inventories, implying that the potential of carbon sink in Sichuan (including Chongqing) forest was increasing. Carbon stock in mature forest showed the declining trend in the study period, which accounted for 64.15%, 63.89%, 65.33%, and 60.82% of the total in the corresponding phase, respectively, while that in young and middle-aged forest showed the opposite, showing that the study forest has a strong potential of carbon sequestration. Meanwhile, the potential of carbon sequestration in the plantation increased continuously although natural forest stored carbon more than 90% for the same stage, resulting that annual increment of carbon stock in the plantation was 7.17% in comparison with 1.83% in natural forest. The results showed that man-made forest played an important role in enhancing forest carbon sequestration in the study region. Furthermore, the results also showed that Sichuan the study forest played an important and irreplaceable role in enhancing national forest carbon sequestration due to higher carbon sequestration in the forest in comparison with national level.
Spatial distribution characteristics of forest soil organic carbon stock in Sichuan Province

HUANG Cong-De,ZHANG Jian,YANG Wan-Qin,ZHANG Guo-Qing,WANG Yong-Jun,

生态学报 , 2009,
Abstract: Forest soil organic carbon plays an important role in global carbon cycle, as a consequence of which much more attentions have been given to the regional forest soil organic carbon stock. As yet little information was available on the spatial pattern of forest soil organic carbon pool in Sichuan Province, which was difficult to make needs of accurately assessing the regional forest soil organic carbon stock, and managing regional forest soil carbon pool. Forest soil organic carbon stock and distribution traits were therefore analyzed by coupling field investigation and ArcGIS methods with the purpose to assess forest soil carbon storage and spatial distribution in Sichuan Province. The total organic carbon stock of Sichuan forest soil was (2394.26±514.15) TgC with average carbon density of 190.45 Mg hm-2. Forest soil organic carbon stock varied from (5.05±0.37) TgC to (1101.74±205.4) TgC, depending upon forest types. Meanwhile, soil organic carbon density ranged from (102.69±21.09) Mg hm-2 to (264.41±49.24) Mg hm-2 in Sichuan forest, depending upon forest types and the altitude, latitude and longitude. Forest soil carbon content, density and stock declined with the increase of soil depth. Soil carbon density increased with the increase of altitude and latitude, but decreased with longitude. The results implied that the measurement of soil organic carbon stock in the forest ecosystem would benefit to enhance the precision in assessing regional forest soil carbon stock.
Effects of thinning on fine root biomass and carbon storage of subalpine Picea asperata plantation in Western Sichuan Province, China

LIU Yun-Ke,FAN Chuan,LI Xian-Wei,LING Yin-Hua,ZHOU Yi-Gui,FENG Mao-Song,HUANG Cong-De,

植物生态学报 , 2012,
Abstract: Aims Fine root carbon storage is an important part of forest ecosystem carbon pools. Our objective was to determine the effects of thinning on fine root biomass and carbon storage in a Picea asperata plantation in Western Sichuan Province, China. Methods We sampled fine roots of a 50 year-old P. asperata plantation thinned by different treatments in August 2010. We excavated soil blocks of 20 cm × 20 cm × 20 cm to sample intact fine root branches of at least the first five branch orders, dissected the intact root branches by order and measured the biomass and carbon storage of each order. Important findings Fine root biomass and carbon storage significantly increased with root order (p < 0.05). The first order roots had the smallest biomass and carbon storage, and the fifth order roots had the largest. Compared with the control, thinning the plantation had significant effects on fine roots biomass and carbon storage (p < 0.05), while the effects of fine roots biomass per plant varied. Thinning treatments of 10% and 20% were not significantly different from the control (p > 0.05). Thinning significantly affected the distribution of fine root biomass in the five root orders. As the thinning intensity increased, the ratio of biomass distribution in the first and second fine order increased. The first order had the largest increase. The ratio of biomass distribution in orders 3 to 5 decreased, and order 5 had the largest decrease. The 50% thinning significantly reduced the fine root biomass ratio in the lower soil layer (20–40 cm), but there was no significant difference compared with 20% and 30% (p > 0.05).
New Method for Images Denoising while Keeping Edge Information

ZHANG Chun-mei,ZHANG Tai-yi,LU Cong-de,

中国图象图形学报 , 2006,
Abstract: The objective of image processing is to denoise while keep the intrinsic imforrnation. A method is proposed for images denoising with double density dual-tree complex wavelet transform. It integrates the advantages of double density wavelet, dual tree wavelet and complex wavelet. It has improved directionality which increased the directions from 6 to 12. The adaptive soft threshold is applied to wavelet coefficients. It could ameliorate the ability of image denoising. The denoising and edge detection for a typical image is carried out. Simulated experiments demonstrate that the proposed approach is effective on image denoising and can keep the edge information at same time. Its mean square deviation is reduced 2.4% compared with the dual-tree complex wavelet.
Magnetar Giant Flares in Multipolar Magnetic Fields --- I. Fully and Partially Open Eruptions of Flux Ropes
Lei Huang,Cong Yu
Physics , 2014, DOI: 10.1088/0004-637X/784/2/168
Abstract: We propose a catastrophic eruption model for magnetar's enormous energy release during giant flares, in which a toroidal and helically twisted flux rope is embedded within a force-free magnetosphere. The flux rope stays in stable equilibrium states initially and evolves quasi-statically. Upon the loss of equilibrium point is reached, the flux rope cannot sustain the stable equilibrium states and erupts catastrophically. During the process, the magnetic energy stored in the magnetosphere is rapidly released as the result of destabilization of global magnetic topology. The magnetospheric energy that could be accumulated is of vital importance for the outbursts of magnetars. We carefully establish the fully open fields and partially open fields for various boundary conditions at the magnetar surface and study the relevant energy thresholds. By investigating the magnetic energy accumulated at the critical catastrophic point, we find that it is possible to drive fully open eruptions for dipole dominated background fields. Nevertheless, it is hard to generate fully open magnetic eruptions for multipolar background fields. Given the observational importance of the multipolar magnetic fields in the vicinity of the magnetar surface, it would be worthwhile to explore the possibility of the alternative eruption approach in multipolar background fields. Fortunately, we find that flux ropes may give rise to partially open eruptions in the multipolar fields, which involve only partial opening up of background fields. The energy release fractions are greater for cases with central-arcaded multipoles than those with central-caved multipoles emerged in background fields. Eruptions would fail only when the centrally-caved multipoles become extremely strong.
Magnetar Giant Flares in Multipolar Magnetic Fields --- II. Flux Rope Eruptions With Current Sheets
Lei Huang,Cong Yu
Physics , 2014, DOI: 10.1088/0004-637X/796/1/3
Abstract: We propose a physical mechanism to explain giant flares and radio afterglows in terms of a magnetospheric model containing both a helically twisted flux rope and a current sheet (CS). With the appearance of CS, we solve a mixed boundary value problem to get the magnetospheric field based on a domain decomposition method. We investigate properties of the equilibrium curve of the flux rope when the CS is present in background multipolar fields. In response to the variations at the magnetar surface, it quasi-statically evolves in stable equilibrium states. The loss of equilibrium occurs at a critical point and, beyond that point, it erupts catastrophically. New features show up when the CS is considered. Especially, we find two kinds of physical behaviors, i.e., catastrophic state transition and catastrophic escape. Magnetic energy would be released during state transitions. The released magnetic energy is sufficient to drive giant flares. The flux rope would go away from the magnetar quasi-statically, which is inconsistent with the radio afterglow. Fortunately, in the latter case, i.e., the catastrophic escape, the flux rope could escape the magnetar and go to infinity in a dynamical way. This is more consistent with radio afterglow observations of giant flares. We find that the minor radius of flux rope has important implications for its eruption. Flux ropes with larger minor radius are more prone to erupt. We stress that the CS provides an ideal place for magnetic reconnection, which would further enhance the energy release during eruptions.
Magnetar Giant Flares and Their Precursors --- Flux Rope Eruptions with Current Sheets
Cong Yu,Lei Huang
Physics , 2013, DOI: 10.1088/2041-8205/771/2/L46
Abstract: We propose a catastrophic magnetospheric model for magnetar precursors and their successive giant flares. Axisymmetric models of the magnetosphere, which contain both a helically twisted flux rope and a current sheet, are established based on force-free field configurations. In this model, the helically twisted flux rope would lose its equilibrium and erupt abruptly in response to the slow and quasi-static variations at the ultra-strongly magnetized neutron star's surface. In a previous model without current sheets, only one critical point exists in the flux rope equilibrium curve. New features show up in the equilibrium curves for the flux rope when current sheets appear in the magnetosphere. The causal connection between the precursor and the giant flare, as well as the temporary re-entry of the quiescent state between the precursor and the giant flare, can be naturally explained. Magnetic energy would be released during the catastrophic state transitions. The detailed energetics of the model are also discussed. The current sheet created by the catastrophic loss of equilibrium of the flux rope provides an ideal place for magnetic reconnection. We point out the importance of magnetic reconnection for further enhancement of the energy release during eruptions.
Fast Sparse Multipath Channel Estimation with Smooth L0 Algorithm for Broadband Wireless Communication Systems  [PDF]
Guan Gui, Qun Wan, Ni Na Wang, Cong Yu Huang
Communications and Network (CN) , 2011, DOI: 10.4236/cn.2011.31001
Abstract: Broadband wireless channels are often time dispersive and become strongly frequency selective in delay spread domain. Commonly, these channels are composed of a few dominant coefficients and a large part of coefficients are approximately zero or under noise floor. To exploit sparsity of multi-path channels (MPCs), there are various methods have been proposed. They are, namely, greedy algorithms, iterative algorithms, and convex program. The former two algorithms are easy to be implemented but not stable; on the other hand, the last method is stable but difficult to be implemented as practical channel estimation problems be-cause of computational complexity. In this paper, we introduce a novel channel estimation strategy using smooth L0 (SL0) algorithm which combines stable and low complexity. Computer simulations confirm the effectiveness of the introduced algorithm. We also give various simulations to verify the sensing training signal method.
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