Cooling slope casting to obtain thixotropic feedstock

Thixoforming, and related semi-solid processing routes for metallic alloys, require feedstock with a non-dendritic microstructure in the semi-solid state. The material then behaves in a thixotropic way in that, when it is sheared it flows and can be forced to fill a die and, when it is allowed to stand it thickens again. The New Rheocasting (the NRC process) is a recently developed semi-solid processing route. There are two versions of this route. In one, molten alloy is poured directly into a tilted mould and, through careful temperature control during cooling, a spheroidal semi-solid microstructure is achieved. The material in the mould is then upended into a shot sleeve and hence forced into a die. Alternatively, the molten alloy is poured onto a cooling slope and thence into a mould before processing. The aim of the work described in this paper was to develop understanding of the microstructural development during the initial stages of this process. The results for pouring A356 aluminium alloy via a cooling slope into a mould are presented

Locating a Mate in 3D: the Case of Temora Longicornis

Using laser optics to illuminate high–resolution video–recordings, we revealed behavioural mechanisms through which males of the calanoid copepod species Temora longicornis locate females. Males of T. longicornis swam at significantly faster speeds than females along more sinuous routes, possibly reflecting adaptations to increase encounter with females. Upon approaching within 2 mm (i.e. two bodylengths) of a female\u27s swimming path, males accelerated to significantly higher pursuit speeds. Pursuit trajectories closely traced the trajectories of females, suggesting that males were following detectable trails created by swimming females. Males of T. longicornis detected female trails up to at least 10 s old, and tracked trails for distances exceeding 13 cm, or 130 bodylengths. Females were positioned up to 34.2 mm away from males (i.e. reactive distance) when males initiated ‘mate–tracking’. It was always the males of T. longicornis that detected and pursued mates. In rare events, males pursued other males. Behavioural flexibility was exhibited by males during mate–tracking. Males generally tracked the trails of ‘cruising’ (i.e. fast–swimming) females with high accuracy, while the pursuits of ‘hovering’ (i.e. slow–swimming) females often included ‘casting’ behaviour, in which males performed sharp turns in zigzag patterns within localized volumes. This casting by males suggested that hovering females create more dispersed trails than cruising females. Casting behaviour also was initiated by males near locations where females had hopped, suggesting that rapid movements by females disrupt the continuity of their trails. Males were inefficient at choosing initial tracking directions, following trails in the incorrect direction in 27 of the 67 (40%) mating pursuits observed. Males usually attempted to correct misguided pursuits by ‘back–tracking’ along trails in the correct direction. Males were observed to detect and track their own previous trajectories without females present, suggesting the possibility that males follow their own trails during back–tracking. Observations of males tracking their own trails and the trails of other males bring into question the specificity of trails as a mechanism promoting reproductive isolation among co–occurring planktonic copepods

Voting and Information Aggregation in Parliamentary and Semi-Presidential Democracies

This paper investigates legislation in parliamentary and semi-presidential democracies where the legislature and the president have formal role in legislation. A proposed law is first voted in the legislature and if it passes, comes to the consideration of the president. I study two prevalent legislative procedures: (i) Single-round legislation where the president's action is final, (ii) Two-round legislation the president's approval enacts the law but after his veto proposal returns to the legislature for rediscussion. In this setup I examine power balance and the efficiency of information aggregation. For this I build a model of strategic voting with incomplete information and analyze different ideological profiles of the president and the homogenous legislature. The president seems powerless in two-round legislation but in equilibrium there are instances he can change the legislation result. Power struggle arises only when the legislature is modernist and the president is conservative. If the legislature is conservative and the president is modernist, the president has no impact on the outcome, but adversely affects informational efficiency. If they have the same ideological bias, the presidential institution is beneficial and the president's existence provides full information aggregation with finite legislature size in single-round legislation. Above results can be generalized to heterogeneous legislature with two types, except full information aggregation is never achieved