Directed arcs

A comprehensive history of ferrous scrap recycling ia the United States beginning ia 1646 has beea pubUshed (3). Some selected eveats of iaterest iaclude the first opea-hearth steel produced (1868) the first commercial direct-arc electric furnace steel produced ia the United States (1906) the first large iaduction furnace iastaHed ia the United States (1914) the first basic oxygen steel produced ia the United States (1954) the rise of continuous casters and scrap-based minimills (1965) the first thin-slab continuous caster at a minimill (1989) U.S. exports and imports of ferrous scrap at record highs (1990) and the end of production of open-hearth steel (1991). 

Arc wire utilizes two continuously fed 1.6-mm dia intersecting wires with a d-c arc maintained between the wire tips as they meet. Compressed gas (usually air) strips the molten metal from the tips and forms a directional spray stream. This process is widely used to spray most metals. Arc wire is the most economical process because of the wire feedstock. Moreover, it utilizes - 10% of the thermal energy of the other spray processes (0.4 vs 6.6 kWh/kg using stainless steel) because of the direct arc heating of the wire tips. 

The first successful direct-arc electric furnace, patented by Heroult in France, was placed in operation in 1899. The patent covered single- or multiphase furnaces with the arcs placed in series through the metal bath. This type of furnace, utilizing three-phase a-c power, was historically the most common for steel production. 

The first direct-arc furnace in the United States was a single-phase two-electrode rectangular furnace of 4-t capacity at the Halcomb Steel Company (Syracuse, New York), which made its first heat in 1906. A similar but smaller furnace was installed two years later at the Firth-Sterling Steel Company in McKeesport, Pennsylvania. In 1909, a 15-t three-phase furnace was installed in the South Works of the Illinois Steel Company, in Chicago, Illinois, which was, at that time, the largest electric steelmaking furnace in the world. It was the first round instead of rectangular furnace and operated on 25-cycle power at 2200 V. 

Electric arc process. Patented by Siemens in 1878, this u.ses an electric current through the metal (direct-arc), or an arc just above the metal (indirect-arc), as a means of heating. It is widely used in the manufacture of alloy- and other high-quality steels. 

Chen N, Klod S, Rapta P et al (2010) Direct Arc-discharge assisted synthesis of CeoH2(C3H5N) a cis-l-pyrrolino Ceo fullerene hydride with unusual redox properties. Chem Mater 22 2608-2615... 

Graph edges oriented in a definite direction which indicates the order of interconnection between the nodes are called directed arcs. Their orientation is indicated by the arrows placed either on the arcs or near them. A graph, a cycle, and a tree containing directed arcs are called directed. A directed cycle is also called a contour. 

FIGURE 14.4 Schematic design of a direct arc electric furnace for steelmaking. The whole unit may be tilted to the side for emptying the finished steel melt. 

Surveying the research efforts made in the past decade two main directions arc discernahle, namely, investigations carried out on as-quenched glassy metals and those where the glassy metals were subjected to different pretreatments and served merely as precursors to catalytically active materials. 

Any edge (s, t) may be thought of as a superposition of two oppositely directed arcs (s,f) and (t,s). Consequently, we may exclude in general the simultaneous occurrence of ordered and unordered vertex pairs in one graph. This exclusion does not affect the variety of types of graphs. The family of representative graphs of polymers (see Section 14) represents an exception to this rule. 

The nonzero elements of A correspond to the edges of Q, Any off-diagonal element Ajk can be charactexized by a definite direction j - k which is determined by the ordering of its indices. For the transposed element the reverse direction must be attributed. Consequently, an edge of a simple grsq>h can be considered as a superposition of two oppositely directed arcs, as already mentioned in Section 1. 

The elements of V) are ordered pairs denoted by e k = 0> which are represented in the diagrams of a digraph T> by directed arcs which point tvom vertex j to vertex 1. This ordering leads to some peculiarities In the matrix representation of a digraph V which are now elaborated. 

Petri Nets and Their Application in FMS Modeling A Petri net (PN) may be identified as a particular kind of bipartite directed graphs populated by three types of objects. These objects are places, transitions, and directed arcs coimecting places to transitions and transitions to places. Pictorially, places are depicted by circles, transitions by bars or boxes. A place is an input place to a transition if a directed arc exists connecting this place to the transition. A place is an output place of a transition if a directed arc exists connecting the transition to the place. Figure 15 represents a simple PN. Where places p and p are input places to transition t, place p is the output place... 

I (P X T) -> N is an input function that defines directed arcs from places to transitions, where N is a set of nonnegative integers. 

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