Deforestation and Biomass Production in Miombo Forest in Huambo (Angola): A Balance between Local and Global Needs

Miombo is one of the most widely distributed ecosystems in Angola, with a great social and environmental value. Thus, the rural population uses the biomass as fuel and miombo provides important ecosystem services, such as its carbon sequestration capacity. The objectives of this work were (i) to assess deforestation in miombo forest in Huambo province (Angola) during the last 20 years, (ii) to evaluate carbon storage capacity of miombo, and (iii) to calculate the charcoal productive capacity of those forests. From 2000 to 2019, 359,130 ha (12.96%) were deforested in Huambo province. Thirty-six woody species were identified as major components of miombo forest, the most frequent being Albizia anthunesiana, Brachystegia spiciformis, Julbernardia paniculata, Monote spp., Brachystegia boemii, Isoberlinea angolensis, Anisophyllea boehmii, Syzygium guineense, and Erythrophleum africanum. The total biomass estimated in miombo forest was 195.05 Mg ha−1 (55.02 Mg ha−1 radical and 140.04 Mg ha−1 area), with a total wood volume of 78.57 m3 ha−1. This represents values of 91.67 Mg ha−1 of accumulated carbon and 336.13 Mg ha−1 of CO2 equivalent. The potential charcoal productivity was 15,359.9 kg ha−1, corresponding to 24.78 trees ha−1. The Annual Allowable Cutting Volume was 10.77 m3 ha−1 year−1, 14.13 m3 ha−1 year−1, 21.17 m3 ha−1, and 32.85 m3 ha−1 year−1 for rotation lengths of 55, 40, 25, and 15 years, respectively, corresponding to a potential annual charcoal productivity of 2107.08 Kg ha−1 year−1, 2762.96 Kg ha−1 year−1, 4139.21 Kg ha−1, and 422.56 Kg ha−1 year−1. However, deforestation rates in the last 19 years and low charcoal productive capacity could compromise the sustainability of the Miombo ecosystem and its value as an ecosystem service provider in the province if appropriate management strategies are not developed.

Identification method for the dynamic cutting force variation of a high energy efficiency milling cutter

The dynamic cutting force of a high energy efficiency milling cutter is an important indicator for evaluating the stability of the cutting energy efficiency. The existing cutting force analysis focuses on the main characteristics and influencing factors of the cutting force variation in the cutting process, ignoring the influence of the variation of the cutting layer parameters with the cutter tooth error in different cutting stages, and the dynamic cutting force variation is uncertain. In this research, the analytical model of the instantaneous cutting volume of a milling cutter was developed in order to obtain the time-frequency characteristics of the instantaneous cutting volume with the cutter tooth error. According to the sudden changes of the cutting force and the milling vibration, the variations were studied in different cutting stages. The dynamic cutting behavior sequences such as the instantaneous cutting volume, milling vibration, and dynamic cutting force were constructed to characterize the mapping relationship between the dynamic cutting behavior of a milling cutter. Based on these approaches, the identification method for the dynamic cutting force variation of a high energy efficiency milling cutter was proposed. The effectiveness of the method was verified by the results of the milling experiment and the dynamic cutting behavior response analysis. The results showed that the proposed method could effectively identify the variation and its control variables for the dynamic cutting force in the cutting process, and the method could provide a scientific basis for constructing the dynamic cutting force model of a high energy efficiency milling cutter.

Exploration and Practice of Volume Fracturing Technology of Shale Oil in Dagang Oilfield

Based on the geological characteristics of the shale oil in the Kong 2 Member of the Cangdong Sag, Dagang Oilfield, and a large number of core experiments and numerical simulations, the displacement and single-stage liquid volume of the fracturing construction were simulated and optimized; in the stratigraphic shale and stratified mixed shale, the reverse mixing mode is adopted, that is, the gel is used for the rock-breaking seam, and then the low-concentration low-damage fracturing fluid system is used to form the complex seam net. Finally, the high-conductivity-producing area near the well is formed by the addition of sand and gel, forming a personalized horizontal well-cut volume fracturing technology in Dagang Oilfield. The application of this technology in shale oil shows that the output of horizontal well is stable after dense cutting volume fracturing, and industrial development can be realized. Microseismic and stable electric field monitoring confirmed the formation of complex network cracks, and achieved significant yield-increasing effects, providing a reference for the efficient exploration and development of China's continental shale oil.

Planning and regulation of pre-final cuttings in Poland – a proposal for change

Scheduling and regulation of the forest use are of much importance in forest management. Decisions regarding the manner, timing, and intensity of tree felling result in long-term effects, as these affect the species and age structure of forests, along with the direction and dynamics of changes in forest resources. Above all, serious doubts concern the way of determining and accounting for the prescribed forest utilization, and in particular, the possibilities of the pre-final cuttings. In recent times, the precise determination of the pre-final cuttings by volume has been given up. According to the law, the area of pre-final cuttings is now obligatory taken into account. Consequently, it is not possible to determine the total volume limiting the amount of timber to be harvested, thus, there is decreased the value of the forest management plan as the document approved by the minister responsible for forestry as well as the basis for forest management. For practical reasons, the specified pre-final cuttings by volume are considered as indicative. Connecting the planned pre-final cutting volume with the expected volume increment of the stand has not been relinquished. In the present paper, the authors called attention to a necessity for further improvement of the medium-term planning of pre-final cutting volume. A need to change the definition of the incidental cutting was emphasized. As said by the authors, the term “incidental cutting” should denote harvesting wood from diseased and dying or dead trees, along with eliminating the effects of tree damage caused by fortuitous events. Accordingly, the incidental cuttings that are inherently unpredictable, should not be directly attributed to pre-final cutting products. Keeping in mind the incidental cuttings, the authors proposed the method of reckoning the forest use, which would allow for correct accounting with regard to the prescribed pre-final cuttings.

Resource-Efficient Machining of Hard Metals

The main requirements of carbide metal working are higher precision and high quality surface which can be fulfilled by electrical discharge machining. This procedure is accompanied with formation of heat affected zones (white layers) during the discharge process negatively. Therefore, the essential post-processing reduces the efficiency of this process and shows the importance of process energy sources (PES) with ultra short discharge in favor of a clearly differentiated cutting volume. By means of simulations of crater geometry and channel expansion the influence of discharge rise time is defined as determining factor for the cut volume and formation of white layers. The technological section presents two different approaches of realizing ultra-short pulses.