The article presents the research results of the performance of wireless multi-hop networks. The analysis of the decrease in performance of such networks depending on the number of hops was performed for three popular transmission techniques used in mesh networks: Hybrid Wireless Mesh Protocol (default routing protocol for 802.11s), Optimized Link State Routing Protocol and Wireless Distribution System. Based on the measurements results, mathematical models for the decreasing of network transmission parameters depending on the number of hops were developed.
Mud samples from two lakes in West Greenland were kept frozen at 18°C for 18 years. When they were thawed, 4 Cladocera species hatched from diapausing eggs: Daphnia pulex (De Geer, 1778), Macrothrix hirsuticornis (Norman et Brady, 1867) and Chydorus arcticus (Rřen, 1987), which are by far the most abundant Cladocera species in the high Arctic north of 74°N. Another species was Alona quadrangularis (O. F. Müller, 1785), which occurs up to 72°N. All these species gave rise to parthenogenetic offspring and produced ephippia within a time frame comparable to an Arctic summer season. Up to 9 other Cladocera species were likely to be present in the original populations, but did not hatch anymore after 12 years.
Foundry technologists use their own style of gating system designing. Most of their patterns are caused by experience. The designs differ from plant to plant and give better or worse results. This shows that the theory of gating systems is not brought into general use sufficiently and therefore not applied in practise very often. Hence, this paper describes the theory and practical development of one part of gating systems - sprue base for automated horizontal moulding lines used for iron castings. Different geometries of sprue bases with gating system and casting were drawn in Solid Edge ST9. The metal flow through the gating systems was then simulated with use of MAGMA Express 5.3.1.0, and the results were achieved. The quality of flow was considered in a few categories: splashes, air entrapment, vortex generation and air contact. The economical aspect (weight of runner) was also taken under consideration. After quantitative evaluation, the best shape was chosen and optimised in other simulations with special attention on its impact on filling velocity and mould erosion. This design (a sprue base with notch placed in drag and cope) is recommended to be used in mass production iron foundries to reduce oxide creation in liquid metal and especially to still metal stream to improve filtration.
Tungsten heavy alloys comprising tungsten, nickel and ferrous were modified, where molybdenum was added in varying weight proportions keeping the ratio of Ni: Fe (8:2) constant. The powders were mixed in a high-energy ball mill and were further fabricated using the spark plasma sintering (SPS) method at a peak temperature of 1000°C with heating rate of 100°C/min. The details of the microstructure and mechanical properties of these various alloy compositions were studied. With the increasing weight composition of the Mo in the alloy, the relative density of the alloy increased with a significant improvement in all the mechanical properties. The yield strength (YS), ultimate tensile strength (UTS) and hardness improved significantly with increase in the proportion of Mo; however, a reduction in elongation percentage was observed. The maximum strength of 1250 MPa UTS was observed in the alloy with a Mo proportion of 24%. The heavy alloy unmixed with Mo has shown distinct white and grey regions, where white (W) grain is due to tungsten and grey region is a combinatorial effect of Ni and Fe. Upon addition of Mo, the white and gray phase differences started to minimize resulting in deep gray and black ‘C’-phase structures because of homogenization of the alloy. The main fracture mode found during this investigation in the alloys was inter-granular mode.