Improved visibility calculations with tree trunk obstruction modeling from aerial LiDAR

Viewshed and line-of-sight are spatial analysis functions used in applications ranging from urban design to archaeology to hydrology. Vegetation data, a difficult variable to effectively emulate in computer models, is typically omitted from visibility calculations or unrealistically simulated. In visibility analyzes performed on a small scale, where calculation distances are a few hundred meters or less, ineffective incorporation of vegetation can lead to significant modeling error. Using an aerial LiDAR (light detection and ranging) data set of a lodgepole pine (Pinus contorta) dominant ecosystem in Idaho, USA, tree obstruction metrics were derived and integrated into a short-range visibility model. A total of 15 visibility plots were set at a micro-scale level, with visibility modeled to a maximum of 50 m from an observation point. Digital photographs of a 1 m² target set at 5 m increments along three sightline paths for each visibility plot were used to establish control visibility values. Trunk obstructions, derived from mean vegetation height LiDAR data and processed through a series of tree structure algorithms, were factored into visibility calculations and compared to reference data. Results indicate the model calculated using trunk obstructions with LiDAR demonstrated a mean error of 8.8% underestimation of target visibility, while alternative methods using mean vegetation height and bare-earth models have an underestimation of 65.7% and overestimation of 31.1%, respectively.     

Evaluation of Horner plot-corrected log-derived temperatures in the Danish Central Graben,North Sea

A small dataset comprising all temperature available data from reliable Horner plots from the Danish Central Graben was examined. Temperatures obtained by extrapolation using standard Horner plots were determined to be lower than true formation temperatures, as interpreted from DST data. Excellent agreement between true formation temperatures and Horner plot temperatures was achieved when the Horner plot temperatures (T_HP) were corrected upward by an amount proportional to the slope (A) of the Horner plot using the equation where the temperatures and the slope are in degrees Celsius. The standard deviation of the error in the corrected Horner plot temperatures was 2.1°C, indicating that this method is consistent. Further studies using larger numbers of Horner plots from a variety of geographic areas should be carried out to test and refine the hypotheses presented here. Efforts also should be made to understand the causes of variability in slopes of Horner plots.     

Vertical distribution of Artemisia halodendron root system in relation to soil properties in Horqin Sandy Land, NE China

Root distribution plays an important role in both vegetation establishment and restoration of degraded land through influencing soil property and vegetation growth. Root distribution at 0~60 cm depth of A. halodendron was investigated in Horqin Sandy Land. Soil organic carbon (SOC) and nitrogen (SN) concentration as well as carbon and nitrogen in root biomass and necromass were measured. Root length density (RLD) was estimated. Total root biomass, necromass and the RLD at 0~60 cm depth was 172 g/m², 245 g/m², and 368 m/m², respectively. Both biomass and necromass of A. halodendron roots decreased with soil depth, live roots were mainly at 0~20 cm (76% of biomass and 63% of root length), while 73% of the necromass was within 0~30 cm depth. N concentration of roots (biomass and necromass) was about 1.0% and 1.5%, respectively. There were significant differences in SOC concentration between soil layers, but insignificant for SN. Soil C/N ratio decreased with depth (P<0.05). C and N storage for belowground system at 0~60 cm decreased markedly with depth; 41.4% of C and 31.7% of N were allocated to the 0~10 cm layer. Root bio- and necromass together contained similar amount of C to that of the soil itself in the top layer. N stock was dominated by soil nitrogen at all depths, but more so in deeper layers. It is clear that differentiating between soil layers will aid in interpreting A. halodendron efficiency in soil restoration in sandy land.     

EDAPHIC PROPERTIES AND FOLIAR ELEMENTAL CONCENTRATIONS FROM SAND PINE (PINUS CLAUSA) POPULATIONS THROUGHOUT FLORIDA

Soil physical and chemical properties, plus foliar elemental concentrations, are reported for surface (5–10 cm) and subsurface (35–40 cm) soil and foliar tissue samples from 20 sand pine (Pinus clausa) populations, 9 from the Choctawhatchee variety on the Florida panhandle and 11 from the Ocala variety on the Florida peninsula. Sand pine occurred exclusively on sandy soils, with mean sand content >97%. Soils generally were low in organic carbon and soil elemental concentrations. Both K and P were below analytic detection limits, whereas Ca and Mg were present at only modest levels. Only soil Al and Fe were relatively abundant. Foliar elemental concentrations indicated pronounced bioconcentration of nutrients by sand pine. Macronutrients (Ca, K, Mg, and P) approached or exceeded levels typical of other southern pine species. Some contrasts in edaphic and foliar tissue properties were apparent between varieties, but contrasts were more pronounced between groups of populations based on both soil color (yellow-sand group) and variety (Choctawhatchee white-sand and Ocala white-sand groups). The yellow-sand group, dominated by inland Choctawhatchee sites on sediments of mixed marine/fluvial origin, possessed less well sorted sand grains, higher clay content, lower pH, and higher levels of soil Al and Fe. The Choctawhatchee white-sand group consisted primarily of coastal dune sites, with well-sorted sands that reflect an eolian substrate. The Ocala white-sand group ranged primarily along the interior sand ridges of central Florida and was intermediate in sedimentological character. Foliar elemental concentrations did not reflect soil elemental patterns. Whereas Ocala samples were significantly higher in P and Mg, Choctawhatchee samples were higher in K, and there were no signficant varietal differences in foliar Ca. [Key words: sand pine, soil elemental concentrations, foliar elemental concentrations, Florida.]     

基于树木年轮信息的千烟洲人工林碳蓄积的动态分析

The authors developed a model to estimate annual tree growth based on tree-ring data (Abbr. TGTRing model) derived from the trunk at 0.5, 1.3 and 2.5 m height. This model was applied to estimate the annual biomass and carbon accumulation of a plantation in Qianyanzhou Red-Soil Hill Comprehensive Development Experimental Station of CAS in Taihe County, Jiangxi Province (Abbr. Qianyanzhou). The results showed that the inflexion points of the biomass and carbon accumulation curves occur at 17 and 18 years of age, respectively, in masson pine, whilst both inflexion points occurred at 15 years in slash pine and Chinese fir. The biomass and carbon accumulation in Chinese fir proved to be greater in the last 20 years than in the other species, with 171.697 t/hm² and 92.29 tc/hm², respectively. masson pine, with a biomass of 133.84 t/hm² and a carbon accumulation of 73.92 tc/hm² was the lowest whilst slash pine was intermediate with a biomass of 147.639 t/hm² (unturpentined) and 135.743 t/hm² (turpentined), and a carbon accumulation of 80.18 tc/hm² (unturpentined) and 73.72 tc/hm² (turpentined). In 2006, the total biomass and carbon storage of the tree stratum of masson pine in Qianyanzhou was 3324.43 t and 14,156.64 tc, respectively, whilst the values for Chinese fir were 1326.97 t and 713.27 tc. For slash pine the total biomass was 14,156.64 t (unturpentined) and 13,015.97 t (turpentined), and the total carbon storage was 7 688.21 tc (unturpentined) and 7068.78 tc (turpentined). Following the shaving of slash pine for resin, the total biomass was reduced by 1140.67 t and the total carbon storage fell by 619.43 tc.     

Effects of Pinus sylvestris var. mongolica afforestation on soil phosphorus status of the Keerqin Sandy Lands in China

Few studies have considered the effects of afforestation on soil phosphorus (P) status in semiarid regions such as the Keerqin Sandy Lands in China, though plantations have been widely established on P-deficient sandy soils to control wind-induced desertification. Phosphorus fractions and acid phosphomonoesterase (AP) activities were compared in the rhizosphere and bulk soils (0–5 and 5–20 cm) under Mongolian pine (Pinus sylvestris L. var. mongolica Litv.) plantations of different ages (15, 22, and 30 years old) and in bulk soils under grasslands to understand soil P behavior with Mongolian pine plantation development and to find out major factors controlling soil P cycling. Stand age and rhizosphere processes had similar effects on the soil P fractions. Labile inorganic P and phosphate absorbed on aluminum and iron oxides were not affected by stand age and rhizosphere processes. Rhizosphere effects of Mongolian pine accelerated the mineralization of organic P by increasing microbial and AP activities. Soil P properties in bulk and rhizosphere soils changed similarly with plantation development. In the first 15 years after afforestation, total organic P, calcium phosphate, labile organic P, microbial biomass P (MBP) concentrations, and AP activities were reduced sharply. About 73% of the reduction in total P came from mineralization of organic P and 24% came from solubilization of calcium phosphate. From 15 to 22 years onward, soil total organic P and calcium phosphate decreased gradually and labile organic P, MBP, and AP activities increased greatly, whereas total inorganic P remained constant. The results suggest that soil P pool was depleted with Mongolian pine plantation development, especially in the early stage. As the dominant form of soil P, organic P was the main source of available P and associated biological processes controlled soil P cycling under Mongolian pine plantations. To ensure sustainability of pine plantations, it is imperative that soil fertility is conserved by adding fertilizer, thinning, and protecting litterfall.     

鲁北平原黄河古河道初步研究

鲁北平原黄河古河道可分为地面古河道(埋藏深度0—8m)和浅埋古河道(埋藏深度8—40m)。两类古河道部大致可分为三条古河道带,呈SW-NE向近平行展布,每带一般宽5—15km,最宽处可达20km。 古河道沉积层主要由细砂或粉砂组成,为古河床之曲流砂堤或天然堤沉积。各期古河道沉积层之顶、底板主要为粘土或亚粘土和淤泥层所构成,为古黄河泛滥相沉积物。 本区古河道按形成时间顺序可分为三期,下部第一期古河道大约形成于晚更新世晚期—全新世早期,中部第二期古河道形成于全新世早—中期,上部第三期古河道形成于全新世中—晚期。     

Effect of sheep grazing on rangeland plant communities: Case study of landscape depressions within Syrian arid steppes

The arid rangelands of Syria cover over half of the nation's landmass. Punctuating this landscape are broad, dry basins, or wadis, and gentle landscape depressions that exhibit localized elevated vegetation productivity and unique edaphic and hydrologic properties. Historically, continuous heavy grazing and aggressive agricultural activities resulted in excessive ecological degradation within these sensitive environments. Information is needed to determine the influence of livestock grazing on plant communities in landscape depressions and the impact that this has on ecosystem resilience. The purpose of this research is to evaluate the effect of short-term sheep grazing on vegetation characteristics and plant community structure within depressions, and to provide recommendations for improved grazing management. Study plots were randomly located within paired topographic depressions located in northwestern Syria. Vegetation samples were collected along transects including plant biomass, plant density, herbaceous cover, and species diversity. In grazed plots, plant biomass was 49 g DM/m² compared to 234.4 g DM/m² in protected plots. Average plant density was 65 plants/m² in grazed plots compared to 1013 plants/m² in protected plots (P = 0.001). Herbaceous cover was 175% higher on protected sites compared to grazed plots. Average diversity (Shannon–Wiener index value) was 0.8 in grazed plots compared to 2.3 in protected plots. These results suggest that plant community structure will be impacted from short-term grazing and that a site's ability to positively respond to disturbance over time may be limited. We conclude that carefully planned grazing management should result in greater plant productivity and diversity.     

川西南干热河谷赤按人工林生物量和营养元素含量

用林木生物量回归方程，求得川西南干热河谷五年生赤桉纯林中乔木层生物量１３１３３．９ｋｇ／ｈａ（年平均生长量８０７９．７ｋｇ／ｈａ），草本层生物量５５２．０ｋｇ／ｈａ（枯落物现存量５９１．６ｋｇ／ｈａ）；赤桉与山毛豆混交林林分生物量２７１８６．９ｋｇ／ｈａ，其中赤桉生物量１６４９４．３ｋｇ／ｈａ（年平均生长量６６２０．２ｋｇ／ｈａ），灌木层生物量１０３６３．６ｋｇ／ｈａ，草本层生物量３２９．０ｋｇ／ｈａ（枯落物现存量１２６４．３ｋｇ／ｈａ）．混交林中赤桉生长好于纯林中赤桉的生长。林分营养元素含量不同植物差别很大，同种植物各器官也有所差别．各器官中营养元素含量顺序一般为：ｃａ＞Ｎ＞Ｍｇ＞Ｋ＞Ｐ，Ｐ是林地土壤缺乏的元素。     

Is exotic plant invasion enhanced by a traditional wildlife habitat management technique?

Soil disturbance is a wildlife habitat management tool that retards succession and promotes early seral vegetation. Our objective was to determine responses of two invasive herbaceous species (Pennisetum ciliare and Salsola iberica) and native perennial grasses to disking on different soils. Two 10 ×40 m plots were delineated within each of 4 blocks on Ramadero loams and 4 blocks on Delmita fine sandy loams. On Delmita soils, canopy cover of P. ciliare, S. iberica, and native perennial grasses averaged across all years was not affected by disking (ANOVA, P>0.05). On Ramadero soils, P. ciliare canopy cover was similar (Tukey's, P>0.05) on control and disked plots for the first 4 years post-disturbance, but P. ciliare cover was 10-fold greater (Tukey's, P=0.02) the 5th year after disking on disked versus control plots. On Ramadero soils, S. iberica canopy cover averaged across all years was 221 times greater (ANOVA, P=0.05) on disked plots than on control plots. Disking did not affect native perennial grass canopy cover. Land managers should consider soil series when disking for wildlife management, as disking disturbance may exacerbate exotic plant ingress and establishment on certain soils.     

Small-scale vegetation dynamics in semi-arid steppe in Inner Mongolia

Small-scale vegetation dynamics were followed for ecotones and in uniform stands inArtemisia-dominated steppe vegetation under grazing and when recovering from heavy grazing. Species composition was followed annually for 5 years in 1 m²and 0·25 m²plots for (1) presence–absence; (2) density; and (3) biomass.More rapid vegetation dynamics, in terms of change of type of vegetation and distance moved in DCA species space between sampling occasions, were observed in smaller plots and in early seral stages, where species were few and alpha diversity low. Only the plots recently protected from grazing showed a directional vegetation change; those protected for more than 3 years and those under continued grazing showed, at this scale, non-directional dynamics.     

A Simple Graphical Technique for Conditional Long Range Forecasting of Below-Average Rainfall Periods in the Tuvalu Islands, Western Pacific

For the Tuvalu Island group in the western Pacific, a simple graphical method is proposed as a means of forecasting whether rainfall totals for the next 1, 2,…,6 months will be below average. The method is based on scatter plots where the points are color-coded as above- or below-average rainfall, with the plot axes being lag-1 and lag-2 NINO4 sea surface temperatures. Within the scatter plots there are reasonably clear data fields with higher frequencies of below-average rainfalls associated with cooler precursor NINO4 temperatures. These data fields are defined by subjectively emplaced separation lines which bifurcate the scatter plots into “predictable” and “unpredictable” fields. If two precursor NINO4 temperature values define a point located in a predictable field then a warning would be issued for below-average rainfall over the next n-month period, depending on the time scale of the scatter plot. A long rainfall record at Funafuti in Tuvalu indicates that success in predictable-field forecasting of below-average rainfalls would range between 68% for 1-month rainfall totals and 89% for 6-month totals. The forecasting success derives from persistence of cooler NINO4 sea surface temperatures which are associated with lower rainfalls in Tuvalu. However, many dry periods are also located in the unpredictable field and cannot be forecast by this method.     

不同强度放牧后自然恢复的沙质草地土壤性状特征

通过对科尔沁沙质草地不同强度放牧后自然恢复过程中土壤的物理、化学和生物学性状特征的研究,结果表明,土壤有机碳、全氮、全磷、有效氮和速效磷含量以及基础土壤呼吸活性在各处理表层土壤的特征为:中牧后恢复草地>轻牧后恢复草地>无牧恢复草地>重牧后恢复草地;重牧后的恢复草地表层土壤较其它处理有较高的土壤容重和pH值以及较低的过氧化氢酶、脲酶和碱性磷酸酶活性;沙质草地的土壤养分和生物学活性在剖面中的分布为上高下低,主要富集于0~ 25cm表层,放牧对土壤系统的影响主要表现在0~ 75cm土层。重度放牧使沙质草地超出了其承载能力和承受干扰的阈限,土壤性状恶化,恢复力降低;而适度的放牧后恢复有利于土壤化学和生物学性状的保持和提高。     

Afforestation effects on soil microbial abundance, microbial biomass carbon and enzyme activity in dunes of Horqin Sandy Land, northeastern China

In order to investigate the effects of afforestation on soil microbial abundance, microbial biomass carbon and enzyme activity in sandy dunes, 20-year-old Pinus sylvestris var. mongolica Litv. (PSM) and Populus simonii Carrière (PSC) mature forests were selected in Horqin Sandy Land, and mobile dunes was set as a control (CK). Results show that PSM and PSC plantations can improve soil physicochemical properties and significantly increase microbiological activity in mobile dunes. Soil microbial abundance, microbial biomass carbon and enzyme activity show an order of PSPSMCK. Total soil microbial abundance in PSM and PSC was respectively 50.16 and 72.48 times more than that in CK, and the differences were significant among PSM, PSC and CK. Soil microbial biomass carbon in PSM and PSC was respectively 23.67 and 33.34 times more than that in CK, and the difference was insignificant between PSM and PSC. Soil enzyme activity, including dehydrogenase (DEH), peroxidase (PER), protease (PRO), urease (URE) and cellobiohydrolase (CEL) in PSM and PSC were respectively 19.00 and 27.54, 4.78 and 9.89, 4.05 and 8.67, 29.93 and 37.46, and 9.66 and 13.42 times of that in CK. P. sylvestris and P. simonii can effectively improve soil physicochemical and microbiological properties in sandy dunes and fix mobile dunes in Horqin Sandy Land. The C mic :C ratio is an applicable indicator to estimate soil stability and soil water availability, and based on an overall consideration of plantation stability and sustainability, P. sylvestris is better than P. simonii in fixing mobile dunes in sandy land.     

Microtopographic properties of sparse moss vegetation in the Antarctic polar desert

The effect of topography on moss vegetation is examined to clarify the processes that affect the colonization of polar deserts on continental Antarctica. Data on the presence of the mosses Bryum pseudotriquetrum and Pottia heimii, and relative altitude were recorded. The altitude measurements were used to infer the underlying topographical attributes of the substrate in the study plots. Specifically, the local distribution of moss plants was clarified using the topographical attributes to construct generalized linear mixed models (GLMMs). The models suggested that steep slopes and convex microhabitats within areas of concave general relief (at the plot scale 4 × 4 m) promoted the establishment of moss. This correspondence to general relief was more apparent for B. pseudotriquetrum than for P. heimii. Among the study plots, general relief was found to be an important determinant of the precise spatial distribution of B. pseudotriquetrum. The standard surface estimated using the robust methods presented in this study is shown to be more accurate for describing moss distribution than the prevailing least-squares method.     

An Advanced Well Log and an Effective Methodology to Evaluate Water Saturation of the Organic-Rich Cambay Shale

Water saturation (S_w) is a vital parameter in the evaluation of hydrocarbon reservoir. Realistic estimation of S_w in shale reservoir is a challenging problem because of the presence of significant clay minerals and organic matter. The present study aims to estimate S_w of organic-rich Cambay Shale, Jambusar–Broach block, Cambay Basin, India, using an effective methodology and improved equation (TOC–clay equation), considering the appropriate corrections to counter the effect of clay minerals and organic matter in modifying resistivity. Advanced log like Litho-scanner has been utilized for the continuous estimation of clay content and total organic carbon (TOC), required for the estimation of S_w. Elemental capture spectroscopy and support vector regression were also applied for evaluation of clay content and TOC in one well where Litho-scanner log is not available. To investigate the effectiveness and applicability of the TOC–clay equation, results of S_w estimated from this equation and various other models have been compared with core S_w for a well. The analysis indicates that S_w derived from TOC–clay equation is having the closest agreement to core S_w data with an average absolute percentage error of 7.9% and coefficient of correlation 0.95. For other models, average absolute errors are significantly higher (16.8–32.7%). The application of TOC–clay equation will be useful for evaluation of the Cambay Shale reservoir. In addition, the resistivity-based TOC–clay equation used in this study is simple with a practical approach; it can be applied easily and efficiently for any organic-rich shale reservoir elsewhere.

     

黑麦草在净化富营养化水的人工湿地生态工程中的作用

在人工湿地生态工程中利用黑麦草(Lolium perenne L．)净化污水，得到了较好的效果。结果表明：利用黑麦草在冬春季节的生长，可使亚热带地区人工湿地常年运行，黑麦草在3—4月份对水体就有明显的净化作用。在春夏季节，特别在5月份黑麦草可以获得较高的生物量和N、P的积累量，因而净化贡献最大。从产草量方面考虑，延长黑麦草的生长期能获得较高的生物量；从植物体所含营养物质状况和饲用价值看，增加收割次数的黑麦草N、P含量高，饲用价值高；但从黑麦草对污水中N、P的吸收和积累量方面考虑，收割次数过高则不利于黑麦草对污水的净化及N、P的累积。从上述几方面综合考虑，在黑麦草整个生长期收割次数以2．3次为宜。     

Recovery rates of microbiotic crusts within a dune ecosystem in the Negev Desert

Despite the important role played by microbiotic crusts in desert ecosystems, data concerning their recovery rates are scarce and are mainly based on estimates that fluctuate between several years to a few hundred years. In order to study the recovery rates of microbiotic crusts inhabiting sand dunes in the western Negev Desert, Israel, annual measurements of chlorophyll, protein, carbohydrates and moss counts were carried out during 1990–1995. Measurements were taken in two pairs of plots (1.5–6.3 m²) established in each north- and south-facing aspect from which the upper 10 cm surface from one plot of each pair was removed. Recovery of the crusts was fast with surface-removed plots showing a complete recovery of chlorophyll a within 6–7 years, of protein within 6–8 years and of carbohydrates within 8–9 years. Recovery of the mosses was slightly longer at 17–22 years. The data are higher than the lower estimates of recovery but much lower than the higher estimates proposed in the literature. The data also suggest that upon prohibition of goat and sheep grazing (and consequently trampling) a relatively rapid stabilization process may take place in the north-eastern Sinai dune field.     

Invasion of the noxious weed Nicotiana glauca R. Graham after an episodic flooding event in the arid zone of Australia

During November 1997, an extreme rainfall event caused flooding in the Olary Creek and created a terminal lake within mallee vegetation on Nagaela Station, far western New South Wales. To assess the effect of this rare event on native flora, six 25×25 m² grazing exclusion plots were established on flooded (4), and un-flooded control (2) areas. We investigated (i) the distribution of Nicotiana glauca in relation to the 1997 flooding event (ii) the variation in density of N. glauca soil-stored seed between soil in control and exclosure plots (iii) the allelopathic effects of N. glauca on germination of Lactuca sativa seeds. Analysis of N. glauca stem sections revealed a maximum of five growth rings, confirming an origin following the 1997 flood event. At a September 1998 assessment, no N. glauca were found across flooded and control plots. In October 2000 N. glauca occurred at densities of 24 and 12 N. glauca seedlings ha⁻¹ in the flooded unfenced and fenced plots respectively. No N. glauca individuals were recorded either from control fenced or unfenced plots. The soil-stored seed study revealed that larger numbers of N. glauca seeds were recovered from the flooded open plot (1936±968) than in flooded fenced plots (856±428.12) but none was found in the control plots. Leachates obtained from dry leaves and twigs had a significantly greater negative impact (p>0.001) on germination of L. sativa seeds than leachates obtained from fresh leaves and bark. This study showed that the density of N. glauca is high in areas where grazing had eliminated competition from native shrubs and grasses. N. glauca is potentially a serious weed along the Olary Creek and ephemeral lake boundaries. Management strategies such as reducing grazing pressure from native and introduced animals and/or effective eradication programs should be adopted, to minimize further infestation.     

Soil freezing process and different expressions for the soil-freezing characteristic curve

The soil-freezing characteristic curve (SFCC), which represents the relationship between unfrozen water content and sub-freezing temperature (or suction at ice-water interface) in a freezing soil, can be used for understanding the transportation of heat, water, and solute in frozen soils. In this paper, the soil freezing process and the similarity between the SFCC of saturated frozen soil and soil-water characteristic curve (SWCC) of unfrozen unsaturated soil are reviewed. Based on similar characteristics between SWCC and SFCC, a conceptual SFCC is drawn for illustrating the main features of soil freezing and thawing processes. Various SFCC expressions from the literature are summarized. Four widely used expressions (i.e., power relationship, exponential relationship, van Genuchten 1980 equation and Fredlund and Xing 1994 equation) are evaluated using published experimental data on four different soils (i.e., sandy loam, silt, clay, and saline silt). Results show that the exponential relationship and van Genuchten (1980) equation are more suitable for sandy soils. The simple power relationship can be used to reasonably best-fit the SFCC for soils with different particle sizes; however, it exhibits limitations when fitting the saline silt data. The Fredlund and Xing (1994) equation is suitable for fitting the SFCCs for all soils studied in this paper.