Crown Height Research Articles

Accuracy of lab scanners in establishing dental measurements: In-vitro study

To determine the accuracy of the measurements made by the lab scanner on rubber-based impressions, the scanned plaster models, and the conventional plaster models by digital vernier calliper. The sample comprised of 20 randomly selected patients. Two sets of maxillary rubber base impressions were taken. The samples were then divided into three groups In Group A, stone casts obtained from the first rubber base impression, were measured manually using a digital vernier calliper having an accuracy of 0.01 mm. In Group B, the second rubber base impressions were measured using a lab scanner (3 shapes series E3) and finally in Group C, the stone models used in group A were scanned by the lab scanner and measurements were performed on 3 Shapes Ortho analyser software. The total of 9 linear measurements made were mesial distal tooth width, arch perimeter, arch length, buccolingual width, clinical crown height, intercanine, inter first premolar, inter second premolar and intermolar distance. The measurements were done twice and average value was recorded as the final result. Data were tabulated and analysed statistically. One way ANOVA test was done to analyse the differences between measurements. Results showed no statistically significant difference between mesial distal tooth width, arch perimeter, arch length, buccolingual width, clinical crown height, intercanine, inter first premolar, inter second premolar and intermolar distance. Digital models were as accurate as the manual measurements performed on casts by digital vernier calliper in establishing linear measurements. Thus, digital models were proven to be reliable and clinically acceptable.

Biting and thermal sensitivity relief of cracked tooth restored by occlusal veneer: A 12-to 24 months prospective clinical study

ObjectivesTo analyze the relief time and risk factors of biting/thermal sensitivity in cracked tooth (CT) restored using occlusal veneer. Methods63 CT were analyzed, and their demographic and clinical data and medical history were collected. Patients were followed-up to examine the relief of thermal/biting sensitivity. ResultsThe maxillary first molar was the most prevalent (N = 25, 40%). The number of crack lines on the finish line ranged from 1 to 6 while the number of crack lines through preparation on the finish line from 0 to 4. Pain relief achieved steadily to 52% for thermal and 62% for biting at 1 week to over 90% for each by 3 months and was completely resolved (no pain) for each by 12 months. Painful of lateral percussion was related to a long period of thermal sensitivity (≥1 month) after restoration with occlusal veneer. The number of crack lines through preparation on the finish line >2 was correlated with biting sensitivity (≥1 month) post-treatment. ConclusionsMost patients (>90%) became asymptomatic of biting and thermal sensitivity within 3 months of CT restored by occlusal veneer. Lateral percussion and the number of crack lines through preparation on the finish line could be significant factors affecting postoperative symptoms. Clinical SignificanceOcclusal veneer is an ultrathin restoration and had no need for restricting clinical crown height, which could protect and relief the biting/thermal sensitivity of CT without preventive root canal therapy.

Assessment of crown dimensions of primary teeth in a selected sample of Indian children - An odontometric study

Abstract Introduction: The size and shape of the tooth are important sources of information for anthropology, forensic odontology, and clinical dentistry. Different populations, and even individuals within the same population, may have variations in the odontometric characteristics of their teeth, which limits the applicability of the data across groups. Aim: To establish the normal odontometric data of primary teeth and examine the sexual dimorphism and its usefulness as a tool to identify the sex among young children. Materials and Methods: This cross-sectional study involved 150 children aged 3–5 years. The parents of the selected children were informed about the procedure protocol of the study and their written consent was obtained. The negative replica of the maxillary and mandibular teeth was obtained and dental casts were prepared. The mesiodistal, buccolingual, and crown height dimensions of each tooth were measured with a digital Vernier caliper. Two independent examiners measured each tooth’s dimensions three times, and the mean was analyzed. Results and Discussion: There was no significant difference between the teeth in the right and left quadrants. Males had larger odontometric dimensions than females. The sex of children based on odontometrics of primary teeth crowns could be determined with an accuracy of 98%, 72%, and 86% using mesiodistal, buccolingual, and crown height dimensions, respectively. Conclusions: There was a clear sexual dimorphism of the primary teeth. The odontometrics can be used as a low-cost and alternative tool for sex identification among children.

Anthropological study of dental indices in Bulgarian population.

A number of derived quantities (called dental indices) that characterize the shape and size of the teeth are calculated between the absolute dimensions of the teeth (mesiodistal, vestibulo-oral, and height of the dental crown).

Factors Associated With Successful Surgical Exposure of Impacted Maxillary Canines

Impacted maxillary canines occur in up to 3% of the population and their eruption is of great importance in establishing, maintaining the shape, aesthetics, and function of the dental arch. Hence, surgical exposure of canines for the purpose of aligning them is a common surgical procedure. This study identifies the frequency and the statistically significant factors associated with successful surgical exposure of impacted maxillary canines and the relative risk factors for repeat surgery. This is a retrospective cohort study of 182 patients who underwent surgical exposure of impacted maxillary canines and orthodontic alignment, over a 5-year period between 2014 and 2018. The variables recorded and analyzed included demographics (age and gender), type of surgery (closed or open exposure), grade of surgeon, and radiographic features on orthopantomogram (canine overlap of adjacent tooth root, vertical canine crown height, canine angulation to midline, position of canine root apex). Outcome data recorded were successful surgical exposure and orthodontic alignment and the need for repeat operation or surgical removal due to ankylosis. The data were analyzed to identify the statistically significant correlates of successful surgical exposure and the relative risk factors associated with repeat surgery. A total of 182 patients and 232 bone-impacted maxillary surgical canine exposures were analyzed, as 50 patients had bilateral impaction. Mean age was 15years (range=10-38years), with 122 (67%) female to 60 (33%) male ratio. Total of 222/232 (96%) impacted maxillary canine teeth were successfully surgically exposed and 10/232 (4%) required re-exposure surgery. Correlates of successful surgical exposures were open exposure technique (P<.002) and reduced distance of vertical canine crown height from alveolar bone margin (P<.033). Relative risk factors for repeat surgery were increased age, male, closed surgical exposure, grade of surgeon, central impaction, increased overlap of adjacent root, increased vertical height, increased angulation to midline, canine apex position above second premolar and procedure done under local anesthetics. This is the largest impacted maxillary canine study to date which has identified the factors that result in successful surgical exposure, hence allow selection of the patients most suitable for this treatment. Secondly, patients with relative risk factors for repeat surgical intervention may be consented appropriately, triaged for a closer orthodontic follow-up and prioritized for surgery to reduce overall treatment time.

Fluid and particle retention in a small New World and a small Old World cervid, the southern pudu (Pudu puda) and Reeves's muntjac (Muntiacus reevesi)

Ruminants differ in the pattern how small particles and liquids pass through their gastrointestinal tract, and in particular their reticulorumen (RR). Based on that they may be classified into ‘moose-type’ and ‘cattle-type’ species (smaller and larger differences between particle and liquid passage, respectively). The ratio between the retention of particles and fluids is called the ‘selectivity factor’ (SF) and is a species-specific characteristic, studied in tragulids, giraffids and bovids, but not in many cervid species. Recently, it has been suggested that a high SF might also serve to wash digesta clean of external abrasives prior to regurgitation for rumination. In this study, we measured SF and passage kinetics (using a liquid marker and markers of different particle size, fed with the diet) in a capreoline deer, the southern pudu (Pudu puda, n = 5, 10.3 ± 2.9 kg, kept at two zoos) and a cervine deer, the Reeves's muntjac (Muntiacus reevesi, n = 6, 11.0 ± 1.7 kg, kept at a research facility). The relative daily dry matter intake (38 ± 3 g/kg0.75 for pudu and 76 ± 5 g/kg0.75 for muntjac) was higher, and the mean retention times (MRT) correspondingly shorter (e.g., MRT small particles in the total digestive tract 39 ± 8 h for pudu and 15 ± 2 h for muntjac), in the muntjac. The SF for small particles/liquid in the reticulorumen were, however, similar for both species, at 1.47 ± 0.21 for pudu and 1.66 ± 0.20 for muntjac, indicating a ‘moose-type’ physiology for both, irrespective of their different phylogenetic origin. To date, SF recorded in bovids attain distinctively higher values than the few reported for cervids. This situation reflects the degree of hypsodonty (tooth crown height) attained by these taxa, which is higher in bovids than in cervids. Together, constraints in hypsodonty as well as SF might limit cervids to more mesic habitats without distinct loads of external abrasives (such as dust or grit) on their food. In both species, some animals showed the typical ruminant pattern of a longer MRT for large than for small particle markers, but in some animals, this difference was not evident. This may be due to variable degrees of marker chewing during ingestion.

Radiographical assessment of post and core placement errors encountered by Saudi dental students at different educational levels

Background: Dental post and core is one of the common procedures performed after endodontic treatment. The aim of this study was to radiographically assess the quality of post and core procedures performed by dental students at different education levels in addition to determining the most critical errors encountered during their clinical practice. Methods: A retrospective cross-sectional study design was conducted in the College of Dentistry, Imam Abdulrahman Bin Faisal University. A total of 550 periapical radiographs (PAs) of cemented posts were retrieved from the records of patients treated by dental students. Parameters and guidelines for assessing the quality of post treatment have been determined and statistically analyzed. A P value &lt;0.05 was considered statistically significant. Results: The study included 502 students and most of them were females (66.5%). Data were obtained from 502 patients (62% females) with fiber posts used in 98.2% of the cases. About 50% of the posts were inserted in premolars, 62.9% in the upper arch, and 66.7% were restored with crowns as a final restoration. Regarding the quality of posts, 98.4% showed good preparation quality and 98% showed good radiographic quality. The post diameter was equal to 1/3 of the root diameter in 31.9% of the cases; post length was equal to 2/3 of root length in 5% of the cases and equal to or more than crown height in all cases (100%). Length of the remaining gutta percha (GP) was between 3–5 mm in 38.8%, and there was no gap between the post and remaining GP in 95.6% of the cases. There were no statistically significant differences between dental students at different clinical educational levels regarding the quality of post placement. Conclusions: The quality of post and core procedures performed by students showed acceptable radiographic quality and were within the recommended standards.

Crown Information Extraction and Annual Growth Estimation of a Chinese Fir Plantation Based on Unmanned Aerial Vehicle–Light Detection and Ranging

Forest biomass dynamics are important indicators of forest productivity and carbon sinks, which are useful for evaluating forest ecological benefits and management options. Rapid and accurate methods for monitoring forest biomass would serve this purpose well. This study aimed at measuring aboveground biomass (AGB) and stand growth from tree crown parameters derived using unmanned aerial vehicle–light detection and ranging (UAV–LiDAR). We focused on 17-year-old Chinese fir plantations in a subtropical area in China and monitored them using UAV–LiDAR from February 2019 to February 2020. Two effective crown height (ECH) detection methods based on drone discrete point clouds were evaluated using ground survey data. Based on the evaluation results, the voxel method based on point cloud segmentation (root-mean-squared error (RMSE) = 0.62 m, relative RMSE (rRMSE) = 4.26%) was better than the tree crown boundary pixel sum method based on canopy height segmentation (RMSE = 1.26 m, rRMSE = 8.63%). The effective crown area (ECA) of an individual tree extracted using ECH was strongly correlated with the annual biomass growth (coefficient of determination (R2) = 0.47). The estimation of annual growth of individual tree crowns based on annual tree height increase (ΔH) derived from LiDAR was statistically significant (R2 = 0.33, p &lt; 0.01). After adding the crown projection area or ECA, the model accuracy R2 increased to 0.57 or 0.63, respectively. As the scale increased to the plot level, the direct model with ECA (RMSE = 1.59 Mg∙ha−1∙a−1, rRMSE = 15.02%) had a better performance than the indirect model using tree height and crown diameter (RMSE = 1.81 Mg∙ha−1∙a−1, rRMSE = 17.10%). The mean annual growth rate of AGB per middle-aged Chinese fir tree was determined to be 8.45 kg∙a−1 using ECA and ΔH, and the plot-level growth rate was 11.47 Mg∙ha−1∙a−1. We conclude that the rapid and accurate monitoring of the annual growth of Chinese fir can be achieved based on multitemporal UAV–LiDAR and effective crown information.

A new Late Miocene Hystrix (Hystricidae, Rodentia) from Turkey.

The Çorakyerler fossil locality in Anatolia reveals unique faunal elements. This study introduces Hystrix kayae sp. nov., a new Late Miocene porcupine initially classified as Hystrix sp. Yavuz etal., 2018. This finding expands our knowledge of Late Miocene Anatolian porcupines, bringing the total number of known species to three. H. kayae sp. nov. is larger than Hystrix aryanensis and exhibits greater upper cheek tooth crown height. Its cheek tooth morphology differs from Hystrix depereti, and it possesses distinctive U-shaped choanae unlike Hystrix primigenia. The Çorakyerler locality may predate sites with H. aryanensis and H. primigenia but aligns temporally with Hystrix parvae localities. This study enhances our understanding of Late Miocene porcupine diversity in Anatolia, emphasizing the importance of Çorakyerler in unraveling the evolutionary history of these fascinating mammals.

Digital and clinical approach to quantifying periodontal tissue changes after crown lengthening surgery: A case series pilot study

Crown lengthening surgery is a common periodontal procedure carried out to increase the amount of tooth exposure for aesthetic or restorative purposes. It is crucial for clinicians to understand the effect of crown lengthening surgery on the periodontal tissues to prevent relapse or over treatment. Even though various clinical parameters have been used by researchers in the past to quantify the amount of suprastructure exposed, the use of digital technology has not been widely adopted. The aim of this case series was to evaluate the changes in periodontal tissue after crown lengthening surgery with both clinical and digital approaches. This case series included five patients who underwent surgery at the Postgraduate Periodontics Clinic at the University of Otago over the period of six months. Clinical parameters such as probing depth, gingival recession, keratinised tissue height, plaque accumulation, gingival inflammation, crown height, gingival phenotype, and bone height were measured with a customised probing stent at baseline and 1-, 3-, and 6-month post-surgery. Digital impressions were also taken along with the clinical parameters to measure the volumetric changes. Most significant changes were observed in crown exposure, gingival recession and bone levels, followed by probing depth reduction for treated sites. Minimal changes were seen for the width of keratinised tissues, plaque levels and gingival scores. Volumetric changes were only significantly reduced after 6 months of healing. This case series found that crown lengthening resulted in an increase in tooth exposure and a reduction in tissue volume. Volumetric changes measured through sequential digital impressions were also comparable to clinical findings.

The Degree of Stability of Rubber Stands (Hevea brasiliensis) in the Timber Estate Area of PT. Sylvaduta District Kembang Janggut, Kutai Kartanegara District East Kalimantan Province

The development of Timber Estate (HTI) is one of the efforts to improve the welfare of the community's interests by considering the balance of the ecosystem. The development of rubber timber estate is expected to be a solution to the problems that hinder the current performance of HTI development, especially the problem of overlapping land tenure and the realization of planting. This is to maintain the fulfillment of the balance of environmental benefits, socio-cultural benefits, and economic benefits. The study's aims were: (1) to determine the percentage of the crown, total and branch-free height; and (2) to determine the stability value of rubber stands in the area of ​​P.T. Sylvaduta Corporation Timber Estate. This research was conducted from April to May 2023 at P.T. Sylvaduta Corporation in Kembang Janggut District, Kutai Kartanegara Regency, East Kalimantan Province. namely in block A1 plot 1 to represent block A , Block E1 tile 3 to represent block E1 and lastly Block G3 tile 5 to represent block G3. A sampling of rubber plants in the area of ​​P.T. Sylvaduta Corporation used a purposive sampling of 150 plants. Data Collection: (1) primary data: Diameter at Chest Height, Tree Height, and Crown length. And (2)secondary data include the following: (1) plant spacing; (2) the year of planting or the age of the plant, and (3) the general condition of the planting site was obtained from direct observations in the field and company documents. The research results show that : (1) the value of the degree of stability and percentage of the rubber plant canopy, namely 51.16% and 64.54%, is in the stable category; and (2) the use of a 3 x 6 m spacing using IRR 118 and PB260 clones had an average diameter at breast height of 20.9 cm, a total height of 10.62 m, a branch-free height of 3.81 m and a crown length of 6.82 m.

Impingement of a water droplet onto a water film on the surface with micro-structures

In the present study, we carried out an experimental investigation of the impacting process of a water droplet onto a water film on the surface with micro-structures. A parameter study of the droplet Weber number, the dimensionless water film thickness, and the dimensionless distance between two micro-protrusions was carefully performed. In addition, the impacting process of a water droplet onto a water film on the flat surface was also measured for comparisons. The results showed that, within the scope of this study, the increase of the dimensionless distance between two protrusions had a minor effect on the crown top diameter evolution and the crown lifetime. In addition, the number of secondary droplets was not monotonously affected by the increase of the dimensionless distance between two protrusions. Under the same droplet Weber number condition, when the water film was relatively thin, the dimensionless distance between two protrusions was found to have apparent influence on the evolution of crown base diameter. Besides, considering the effect of the dimensionless distance between two protrusions, we proposed a modified energy loss factor as well as two correlations for the maximum dimensionless crown height and the time to reach the maximum height.

Characterizing wind-induced reconfiguration of coaxial branched tree

Tree dynamics have been extensively studied because of their reconfiguration ability under oncoming wind flow. However, there is still a gap in the effect of crown configuration on the tree reconfiguration. The present study examined the wind-induced reconfiguration performance of 9 coaxial branched trees with three different pruning techniques by wind tunnel tests, to comprehensively and thoroughly reveal the effects of crown configurations on tree reconfiguration. Results showed that normalized crown mass is the best parameter for correlating with the maximum normalized drag force acting on the tree. Meanwhile, it was found that area reduction effect decreases with an increase in LAI1 (the ratio of leave area and ground area) and LAI2 (the ratio of leave area and frontal area). Streamlining effect is gradually enhanced with an increase in λct (the ratio of crown height and trunk height), but shows a trend of first increasing and then decreasing with the increase of LAI1 and LAI2. Finally, a reconfiguration model was proposed to show the dynamic behavior of the coaxial branched tree under different dimensionless tree parameters. The revealed tree reconfiguration mechanism and the reconfiguration model can guide tree managers and researchers for understanding the tree behavior and tree dynamics.

Picturing local adaptation: Spectral and structural traits from drone remote sensing reveal clinal responses to climate transfer in common-garden trials of interior spruce (Picea engelmannii × glauca).

Common-garden trials of forest trees provide phenotype data used to assess growth and local adaptation; this information is foundational to tree breeding programs, genecology, and gene conservation. As jurisdictions consider assisted migration strategies to match populations to suitable climates, in situ progeny and provenance trials provide experimental evidence of adaptive responses to climate change. We used drone technology, multispectral imaging, and digital aerial photogrammetry to quantify spectral traits related to stress, photosynthesis, and carotenoids, and structural traits describing crown height, size, and complexity at six climatically disparate common-garden trials of interior spruce (Picea engelmannii × glauca) in western Canada. Through principal component analysis, we identified key components of climate related to temperature, moisture, and elevational gradients. Phenotypic clines in remotely sensed traits were analyzed as trait correlations with provenance climate transfer distances along principal components (PCs). We used traits showing clinal variation to model best linear unbiased predictions for tree height (R2 = .98-.99, root mean square error [RMSE] = 0.06-0.10 m) and diameter at breast height (DBH, R2 = .71-.97, RMSE = 2.57-3.80 mm) and generated multivariate climate transfer functions with the model predictions. Significant (p < .05) clines were present for spectral traits at all sites along all PCs. Spectral traits showed stronger clinal variation than structural traits along temperature and elevational gradients and along moisture gradients at wet, coastal sites, but not at dry, interior sites. Spectral traits may capture patterns of local adaptation to temperature and montane growing seasons which are distinct from moisture-limited patterns in stem growth. This work demonstrates that multispectral indices improve the assessment of local adaptation and that spectral and structural traits from drone remote sensing produce reliable proxies for ground-measured height and DBH. This phenotyping framework contributes to the analysis of common-garden trials towards a mechanistic understanding of local adaptation to climate.

Crown root ratio and angulation of various permanent teeth in patients with and without cleft lip/palate

ABSTRACT Aims and Objectives: The purpose of this study was to analyze parameters of tooth in subjects with nonsyndromic cleft lip and palate (CLCP) and to compare the findings with the control groups. Teeth in the cleft-affected and nonaffected side in the same unilateral cleft lip and palate (ULCP) patient were also compared. Materials and Methods: The study included 200 subjects in the age group of 12–37 years who were divided into two groups: nonsyndromic CLCP and control group. The control group was further subdivided into skeletal Class I, II, and III subgroups based on ANB, AO-BO, and overjet, respectively. Crown height, root length, total tooth length, crown root ratio (C/R ratio), and tooth angulations of maxillary permanent central incisors, canines, 1st premolars, and 1st molar were measured on orthopantomograms using both ITK SNAP software and manual tracing. Results: Crown heights significantly increased while root lengths significantly decreased in the CLCP patients when compared to control groups. Total tooth lengths of central incisor, canine, and 1st premolar in CLCP patients were found to be decreased significantly. C/R ratios of all the teeth of nonsyndromic CLCP group irrespective of the cleft affected or nonaffected side was found to be increased as compared to the control groups. There was a significant difference seen in crown height, root length and mesiodistal tooth angulations in the cleft affected side when compared to the non affected side in a UCLCP patient’s dentition. However the total tooth length and the C/R ratio were not affected. Conclusion: Common findings of CLCP are aberrant teeth development, altered tooth morphology, and malformed teeth. The severity of cleft has an impact on the tooth development and morphology as it was observed that delayed root development and short roots, decreased total tooth length, increased C/R ratio and variations in teeth angulations in CLCP patients were affected by the presence and severity of cleft.

Numerical analysis of nonlinear interaction between a gas bubble and free surface in a viscous compressible liquid

Liquid viscosity has a potential effect on bubble dynamics. This paper is concerned with bubble dynamics in a compressible viscous liquid near the free surface. The liquid–gas flow is modeled using the Eulerian finite element method coupled with the volume of fluid method. The numerical results have been shown to be in excellent agreement with those from the spherical bubble theory and experiment. Parametric studies are carried out regarding the Reynolds number Re and the stand-off parameter γd. It clearly demonstrated that the liquid viscosity inhibits bubble pulsation, jet flow, free surface jet, and bubble splitting. Quantitatively, as Reynolds number Re decreases, the maximum bubble volume, jet tip velocity, free surface spike, and crown height decrease, and the toroidal bubble splitting weakens. As the stand-off parameter γd increases, the maximum bubble volume, jet velocity, and bubble average pressure peak increase while the height of the free surface spike decreases. Close observation reveals that the free surface crown tends to disappear at small Re or large γd, further indicating the complex mechanism behind the crown spike evolution.

Three Dimensional Evaluation of Accuracy of Bracket Positioning.

The success of orthodontic treatment depends on accurate bracket placement, so researchers are constantly exploring new direct and indirect bonding methods with the help of cutting-edge imaging technologies like cone beam computed tomography (CBCT), which provides full three-dimensional visualization of tissues down to the root of the tooth. The primary goals of this analysis are to determine the degree of section angulation and adhesive thickness, as well as the accuracy of the vertical and flat section positions. The correlation between total clinical crown height, minor edge to focus of section, and minimum edge to complete curve crown length is one of several possible goals of this investigation (FACC). Currently, 10 patients aged 15-30 who needed fixed appliance treatment were enrolled in an in vivo research conducted by the orthodontics department. Cases with and without extractions of the crooked teeth were counted. Full mouth analysis is being used in this investigation. Ten patients were selected at random and placed in either Group A (the study group) or Group B (the control group) (control group). Group A bonds are more indirect, whereas group B bonds are more like "normal" direct bonds. We used a Canon 700D camera, a biocompatible transparent 3D printing resin, and a 3M Gemini MBT.022 in bracket kit for CT scanning and imaging. Brackets are placed by experienced orthodontists in both treatment groups. There is a statistically significant (P 0.05) difference between the indirect and direct bonding group when all five factors are taken into account, with the indirect bonding group demonstrating superiority in terms of accuracy. The results of the current investigation support the premise that there is a clinically significant difference between direct bonding and 3D indirect bonding in terms of bracket placement accuracy.

Pengaruh Ekstrak Daun Senduduk Bulu (Clidemia hirta L.) terhadap Perkecambahan dan Pertumbuhan Gulma (Praxelis clematidea)

Weeds are plants whose existence is not expected by farmers because they interfere with cultivated plants. But there are weeds that can produce phenolic compounds such as Clidemia hirta L which can be used as bioherbicides. This study aims to determine the effect of Clidemia hirta L. leaf extract on the germination and growth of Praxelis clematidea weeds. The research was carried out from June 2021 to September 2021 at the Weed Science Laboratory and Integrated Field Laboratory, Faculty of Agriculture, University of Lampung. This study used a completely randomized design (CRD) method with 6 treatments with concentrations of Clidemia hirta L leaf extract, namely 0; 1.5; 3.0; 4.5; 6.0; and 7.5%. Each treatment was repeated 6 times to obtain 72 experimental units. The observed variables are germination, crown height, root length, dry weight, and weed poisoning level. The data obtained were analyzed by analysis of variance and continued with the Least Significant Difference Test (LSD) at the 5% level. The results showed that the germination of Praxelis clematidea weed was significantly inhibited by the treatment of Clidemia hirta L leaf extract with a concentration of 1.5; 3.0; 4.5; 6.0; and 7.5%. While concentrations of 3.0%, 4.5%, 6.0%, and 7.5% Clidemia hirta L. leaf extract inhibited the growth of Praxelis clematidea weeds in the greenhouse. Key words: Clidemia hirta L., extract, Praxelis clematidea, germination, growth

Effects of prescribed burning on understory Quercus species of Pinus yunnanensis forest

IntroductionPositioning studies on prescribed burning in Pinus yunnanensis forests have been conducted for several years, focusing on the effects of fire on the composition and structure, growth, regeneration, relative bark thickness, and bark density of understory oak species in Pinus yunnanensis forests.MethodsThe study was conducted on Zhaobi Mountain, Yi-Dai Autonomous County of Xinping, Yuxi City, Yunnan Province. In the prescribed burn after restoration of full 1 year of the area and did not implement the prescribed burn area were set up 10 m × 10 m sample plots 30 pairs of comparisons, and all the oak trees in the sample plots were recorded, each sample plot in the four apexes and the middle were set up five 2 m × 2 m small sample squares, the shrubs in the small sample squares for each plant survey, comparison, statistics and analysis of all data.ResultsThe study results showed that (1) prescribed burning significantly affected the species composition of the understorey of Pinus yunnanensis forests. In both tree and shrub layers, the important values of Quercus aliena, Quercus serrata, Quercus fabri, and Quercus variabilis were significantly reduced in the burned areas. In contrast, the important values of Quercus acutissima increased somewhat. (2) The under crown height of oak trees in the burned areas was significantly lower than in the burned areas, but the height of oak trees in the burned areas was not significantly different from that in the burned areas. In the shrub layer, the height and cover of oak plants in the prescribed burning areas were significantly lower than in the unprescribed burned areas, effectively reducing the vertical continuity of the forest surface combustible material and reducing the possibility of fire converting from surface to canopy fire along the “ladder fuel.” (3) The regeneration of oak plants in the burned area is mainly by sprout tillers, and very few young sprouts are regenerated by seed germination. Renewed young sprouts are difficult to survive the prescribed burn areas the following year due to their lack of fire tolerance. (4) The relative bark thickness and density of oak plants in prescribed burn areas were significantly higher than those in unprescribed burn areas due to the fire tolerance exhibited by oak plants in long-term prescribed burns.DiscussionPrescribed burning has profoundly altered the structural composition and growth of oak plants in the understory of Pinus yunnanensis forests, and oak plants have shown significant fire-adapted traits to resist fire under long-term fire disturbance. The study can provide a scientific basis for prescribed burning, forest fuels, and forest fire management.

Mechanism Analysis of the Influence of Structural Parameters on the Hydraulic Performance of the Novel Y-Shaped Emitter

As a key component of a drip irrigation system, the performance of drip irrigation emitters is determined by the flow channel structures and parameters. In this paper, a novel Y-shaped labyrinth-channel emitter was proposed, and the influence of the hydraulic performance was researched under different waist-arc angles (α) and ratios of crown height to chord length (a:b). The flow characteristics and energy dissipation mechanisms of water in the emitter were analyzed by using fluid dynamics software. The analysis showed that, keeping the ratio of crown height to chord length unchanged and with an increase in the waist-arc angle from 90° to 180°, the pressure-drop ratio before and after the water flow through the vortex area increased, and the hydraulic performance of the emitter was improved, specifically: the design flow could be reduced by 6.02–26.7%, and the slope of the curve could be reduced by 9.83–28.1%. The smaller the ratio of crown height to chord length, the weaker the influence of waist-arc angle was on the design flow and hydraulic performance. Keeping the waist-arc angle unchanged, there was a decrease in the ratio of crown height to chord length from 6:30 to 1:30, the vortex strength inside the emitter channel increased, and the hydraulic performance was improved: the design flow could be reduced by 7.56–23.5%, and the slope of the curve could be reduced by 5.43–20.5%. The bigger the waist-arc angle, the weaker the influence of the ratio of crown height to chord length was on the design flow and the hydraulic performance, even to the point of having no effect. When the Y-shaped emitter was close to the pressure-flow curve slope of the commonly-used triangular-channel emitter, the hydraulic performance of the two was similar, and the former could increase the channel width by 25%, as compared to the latter, or shorten the channel length by 44.3%. The results showed that the Y-shaped emitter had better hydraulic performance compared with the triangular-flow-channel emitter commonly used today. Therefore, the Y-shaped emitter has broad application prospects in water-saving irrigation.