Process control based on double-side image sensing of keyhole puddle for the VPPA welding of aluminum alloys

The double side image sensing of the keyhole puddle in the variable polarity plasma arc welding of aluminum alloys has been investigated in this paper, to extract the characteristically geometrical size of the keyhole and to realize the feedback controlling for weld formation in the welding process. Some geometrical sizes of the visible keyhole in the front and back images such as the width, height, area, etc. can be used to monitor both the keyhole puddle and the weld formation in the welding process. Under the condition of the varied heat sink, varied gap and misalignment, the trend from normal welding to cutting can be reflected from the variations of geometrical sizes of the keyhole puddle respectively. The keyhole area, the keyhole height and the shape parameters of the keyhole puddle are the key parameters which reflect the trend from normal welding to cutting when meeting the condition of the varied heat sink, varied gap and misalignment respectively. The algorithm for the image processing of the keyhole puddle and the periphery extracting of the visible keyhole developed in the paper can be used to determine real timely the geometrical sizes of the visible keyhole. Artificial neural network is applied to establish the model for predicting the geometrical sizes of the back keyhole puddle. The inputs of the model are the geometrical sizes of the front keyhole puddle and the weld parameters, the outputs of the model are the geometrical sizes of the back keyhole puddle. The model can be used to control the stability of keyhole and the weld formation.

Low-temperature charged impurity scattering-limited conductivity in relatively high doped bilayer graphene

Based on semiclassical Boltzamnn transport theory in random phase approximation, we develop a theoretical model to investigate low-temperature carrier transport properties in relatively high doped bilayer graphene. In the presence of both electron–hole puddles and band gap induced by charged impurities, we calculate low-temperature charged impurity scattering-limited conductivity in relatively high doped bilayer graphene. Our calculated conductivity results are in excellent agreement with published experimental data in all compensated gate voltage regime of study by using potential fluctuation parameter as only one free fitting parameter, indicating that both electron–hole puddles and band gap induced by charged impurities play an important role in carrier transport. More importantly, we also find that the conductivity not only depends strongly on the total charged impurity density, but also on the top layer charged impurity density, which is different from that obtained by neglecting the opening of band gap, especially for bilayer graphene with high top layer charged impurity density.

Effects of puddling on percolation and rice yields in rainfed lowland paddy cultivation: Case study in Khammouane province, central Laos

We investigated the effects of puddling on percolation and rice yields in rainfed lowland paddy cultivation. We selected a study village in Khammouane province, central Laos, and set up non-puddling and puddling plots from high to low positions. Even when puddling was conducted carefully, the ponding water in the plots disappeared in the case of little rainfall. Further, percolatifons during the later periods of rice growth increased drastically. Therefore, it is difficult to overcome drought stresses only by conducting puddling. We also compared the water conditions in the non-puddling and puddling plots. In the puddling plots at high position and low position along a stream, the number of days without ponding water in the puddling plots was less than that in the non-puddling field in July, suggesting the possibility of a different transplanting date. We tried to estimate the effects of transplanting date on the rice yields and found that transplanting 15 days earlier leads to an increase of 0.5 t/ha in the rice yields. Moreover, the profits from the increased yields exceed the puddling costs considerably, leading to a definite increase in income. Because the transplanting date has no effects in the fields with high ground water, puddling is effective in paddy fields where ponding does not occur to a significant degree.

Runoff Harvesting and Storage for Rice Crop at Hamelmalo, Semiarid Region of Eritrea

Rice is staple food in Eritrea but it is not cultivated in the country due to semiarid conditions. However, possibilities exist for growing rice using runoff produced from nonagricultural hilly lands, which occupy >50% - 80% area of all agricultural watersheds in Eritrea. Study was undertaken in 6 ha watershed at Hamelmalo to design and develop waterway for safe harvesting of runoff from 5.5 ha catchment into a pond for facilitating runoff farming of rice in 0.5 ha field at the outlet end receiving recurrent floods. Slope of the catchment ranged from 1% to 6%. The waterway was designed to intercept and carry runoff from two major drains in nonagricultural land together and delivering into a pond made adjacent to rice field. The waterway was about 323 m long with 3 m top width, 1.5 m bottom width and 0.3 - 0.8 m depth from surface. The pond was 60 m long, 9 m wide and 1 m deep with 1.5 m high earthen dam towards rice field using soil excavated from the pond. Embankment on the remaining sides was mango orchard land slopping towards pond. The dam base width was 4 m, top width was 2.5 m and height was 1.5 m from the ground surface. Two spill ways were provided in the dam at ends at the ground level to facilitate release of runoff from the pond for irrigation. Gross capacity of pond was >1000 m3. Combined effect of river water, percolation from pond and wetter rice field raised groundwater table from 3.25 m depth in June to 1.4 m by mid-crop season. This resulted in soil wetness exceeding field capacity below 0.7 m depth and greener crop. Rice yields exceeding 2000 kg·ha-1 were harvested under runoff farming conditions. Soil puddling was more conducive to rice crop than compaction under available soil and water resources.

Effect of Puddling and Compaction on Water Requirements of Rice at Hamelmalo, Eritrea

Eritrean farmers can cultivate rice by harvesting runoff from >82% available non-agricultural land in agricultural watersheds for crop use and reducing percolation through optimization of tillage. Experiments were conducted with NERICA rice, N11, to optimize irrigation requirements and puddling and compaction to reduce percolation. Experimental field was adjacent to Anseba River at downstream end of the watershed and a pond on the upstream to intercept runoff. Irrigation treatments were runoff farming with maximum runoff application depth of 10 mm (I1), and 50 mm irrigation two (I2), five (I3), and seven (I4) days after disappearance of ponded water in main plots and puddling by one (T1), two (T2) and three (T3) passes of puddler and compaction by three (T4), four (T5) and five (T6) passes of 600 kg roller in sub plots in 3 replications. Soil profile was loam in the surface 0.45 m and coarse sandy loam below forming porous belt. Soil submergence was difficult to maintain, but water table was developed in soil profile due to inflow of seepage from the river and pond. Depth to the water table was within 1.5 ± 0.1 m for >2 months and receded down to 1.7 m by crop maturity. Soil wetness was near field capacity around 0.7 m depth and increased below due to natural sub-irrigation from the water table. Rice roots penetrated 0.8 m in the puddled plots and 0.7 m in the compacted plots. Residual soil moisture of 135 - 146 mm·m-1 after rice harvesting provides opportunity for planting rapeseed mustered following rice. Puddling was superior to compaction in loam soil. Puddling twice and irrigation 50 mm 7 days after ponded water vanished from surface was sufficient for optimum rice grain yield of 4346 kg·ha-1 and straw yield of 4458 kg·ha-1. Optimum puddling and irrigation schedules reduced crop duration by 6 days without significantly affecting yield. Production function showed that rice grain yield of 4789 kg ha-1 could be obtained by 1009 mm applied water through rainfall and irrigation.

Optimization of working parameters for puddling and flatting machine in paddy field

In order to improve the soil preparation quality,a wide puddling and flatting machine for paddy field was designed with the functionality of tillage,soil crushing,puddling,burying stubble and flatting in one-time operation,which can be equipped on tractors with high power.This study focused on the design and analysis of key components of the machine including puddling equipment,flat shovel and balance structure.Optimal results with field trials and response surface analysis showed that the machine can operate optimally when the working speed,puddling depth and angle of flat shovel were 1.05 km/h,16 cm and 31.30°,respectively.The surface flatness standard deviation was 3.7 cm,and slurry degree was 1.03 g/cm3.Field validation test results were consistent with the optimal parameters,which was able to meet agronomic requirements of mechanical planting in China.