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Source-controlled routing has been proposed as a way to improve flexibility of future network architectures, as well as simplifying the data plane. However, if a packet specifies its path, this precludes fast local re-routing within the network. We propose SlickPackets, a novel solution that allows packets to slip around failures by specifying alternate paths in their headers, in the form of compactly-encoded directed acyclic graphs. We show that this can be accomplished with reasonably small packet headers for real network topologies, and results in responsiveness to failures that is competitive with past approaches that require much more state within the network. Our approach thus enables fast failure response while preserving the benefits of source-controlled routing.
Linear oligophenylene diynes containing 6, 9, and 12 phenylene rings were synthesized in high yields using the nucleophilic aromatic substitution (S(N)Ar) of perfluoroarenes by aryllithium reagents as the key carbon-carbon bond-forming reaction. This reaction was demonstrated to proceed readily at low temperatures with sterically hindered substrates and in the presence of base-sensitive silylalkynyl groups. Diynes synthesized by this methodology were readily zirconocene-coupled into large dimeric macrocycles using the zirconocene reagent Cp(2)Zr(py)(Me(3)SiC triple bond CSiMe(3)).
Nihil humanum alienum estBaruch Spinoza Sorte de Bildungsroman sociologico-pugilistique qui retrace une expérience personnelle d’initiation à un métier du corps aussi reconnu pour sa symbolique héroïque – Mohammed Ali est sans nul doute, avant même Pelé, l’homme vivant le plus célèbre et célébré de la planète – qu’il est méconnu dans sa réalité prosaïque, ce livre est aussi une expérimentation scientifique. Il voudrait offrir une démonstration en actes de la fécondité d’une approche qui prend...
To the degree that physician commitment is possible, systems should appeal to physicians' calculative motivations using extrinsic rewards rather than normative involvement in the organization.
Reforming the international monetary system is a game that any number can play. The second half of the 19 th century saw a series of international monetary conferences designed to place the leading European countries on a common monetary standard. The 1920s saw the Brussels and Genoa Conferences. 1944 saw Bretton Woods. 1967 saw the creation of Special Drawing Rights, which US Treasury Secretary Henry Fowler hailed as “the most ambitious and significant effort in the area of international monetary affairs since Bretton Woods.” 1968 saw the creation of the two-tier gold market, which President Johnson welcomed as “the most significant reforms of the international monetary system since Bretton Woods.” 1971 saw the Smithsonian Agreement, which President Nixon lauded as “the most significant monetary achievement in the history of the world.” The point being, of course, that none of these international agreements fundamentally changed the trajectory of the international system. The most striking feature of the international monetary system from an historical perspective is continuity rather than change. Over this period the international system evolved from a gold standard to a gold exchange standard, to a gold-dollar standard, and then to a dollar standard. It is evolving now into a multiple reserve currency system. International monetary conferences and official initiatives can influence the system at the margin, both for better or for worse, but the “actually existing system” (to invoke language derived from a very different context) reflects a powerful underlying market logic. It is the thesis of this paper that a multiple reserve currency system is coming. The system for which we need to prepare is one in which the dollar, the euro and the renminbi will all be consequential international and reserve currencies. The international monetary system is growing more multipolar because the world economy is growing more multipolar. After World War II, when the United States (US) accounted for the majority of the industrial production of the non-Soviet world, it made sense that the dollar was the principal unit in which exporters and importers invoiced and settled their trade, in which international loans were extended, and in which central banks held their reserves. But this situation makes less sense today when the US accounts for only some 20 per cent of the combined output of countries engaged in international transactions. Because habits die hard, the dollar continues to play a disproportionately important role. But simply because this is true today does not mean that it will be true tomorrow. Countries that trade with and borrow from the euro area will increasingly seek to hold euros as reserves. Countries that trade with and borrow from the PRC will similarly seek to hold renminbi, if not today then in the not-too-distant future.
Recent research indicates that multi-hop wireless networks can suffer from extreme imbalances in the throughput achieved by simultaneous competing flows. We address this problem by designing a practical distributed algorithm to compute a time-slot based schedule that provides end-to-end max-min fairness. Our system uses randomized priorities based on local weights to arbitrate access between nodes that directly compete with each other (we call this weighted slot allocation or WSA). The local weights are in turn computed by a higher layer called end-to-end fairness using local weights (EFLoW). EFLoW implements an additive-increase multiplicative-decrease (AIMD) algorithm that can automatically adapt to changes in traffic demands and network conditions. In each iteration, EFLoW only uses state obtained from within a given node's contention region. We have implemented WSA and EFLoW in both a simulator and a real system by using the overlay MAC layer (OML). Unlike previous work on end-to-end fairness, our approach does not use a centralized coordinator and works for traffic patterns with any number of sources and sinks. Also, since we compute both the fair allocation and a schedule to achieve it, we do not make any assumptions about the efficiency of carrier-sense (CS) based MACs - this is very important in the light of recent work which shows that current CS-based MACs can be very unfair even when all nodes are limited to sending at their fair rate. Our results show that WSA and EFLoW can prevent starvation of flows and improve fairness without sacrificing efficiency for a wide variety of traffic patterns.
The ruthenium triflate complex Cp*(PiPr3)RuOTf (1) was generated from the reaction of Cp*(PiPr3)RuCl with Me3SiOTf in dibutyl ether. Complex 1 reacted with primary and secondary silanes to produce a family of Ru(IV) silyl dihydride complexes of the type Cp*(PiPr3)Ru(H)2(SiRR′OTf) (3–12). Structural analyses of complexes 8 (R = R′ = Ph) and 12 (R = R′ = fluorenyl) revealed the presence of a tetrahedral silicon center and a four-legged piano stool geometry about ruthenium. Anion abstraction from Cp*(PiPr3)Ru(H)2(SiHROTf) by [Et3Si·toluene][B(C6F5)4] afforded hydrogen-substituted cationic ruthenium silylene complexes [Cp*(PiPr3)Ru(H)2(═SiHR)][B(C6F5)4] (R = Mes (13), R = Si(SiMe3) (14)) that display a significant Ru–H···Si interaction, as indicated by relatively large 2JSiH coupling constants (2JSiH = 58.2 Hz (13), 2JSiH = 37.1 Hz (14)). The syntheses of secondary silylene complexes [Cp*(PiPr3)Ru(H)2(═SiRR′)][B(C6F5)4] (R = R′ = Ph (15); R = Ph, R′ = Me (16), R = R′ = fluorenyl (17)) were also achieved by anion abstraction with [Et3Si·toluene][B(C6F5)4]. Complexes 15–17 do not display strong Ru–H···Si secondary interactions, as indicated by very small 2JSiH coupling constant values.
In 2008, Williams et al. reported the discovery of the fourth fundamental passive circuit element, memristor, which exhibits electrically controllable state-dependent resistance [1]. We show that one of the first wireless radio detector, called cat's whisker, also the world's first solid-state diode, had memristive properties. We have identified the state variable governing the resistance state of the device and can program it to switch between multiple stable resistance states. Our observations and results are valid for a larger class of devices called coherers, which include the cat's whisker. These devices constitute the missing canonical physical implementations for a memristor (ref. Fig. 1).
This paper describes the philosophy, application, and implementation of a collection of FORTRAN IV computer programs currently being used in a sophomore course on nonlinear circuit analysis at Purdue University. Since these programs were developed from the education rather than the user point of view, some of them were deliberately designed in the form of a series of subroutines, and were stored in a common disk file. These subroutines and programs are used to analyze a large class of nonlinear electronic circuits such as waveshaping networks, multivibrators, time-base generators, etc. Since the computer is used to take over only the nonconceptual but otherwise very time-consuming task, the students were found to be much more receptive and motivated in learning new concepts. The results reported in this paper are based on the experiences and reactions of approximately 150 students using the batch-processing mode. A short description, however, is also given on a forthcoming experiment to be conducted at Purdue University on the merits of using an on-line graphic display console.
