Chain Reduction for Binary and Zero-Suppressed Decision Diagrams

Chain reduction enables reduced ordered binary decision diagrams (BDDs) and zero-suppressed binary decision diagrams (ZDDs) to each take advantage of the others' ability to symbolically represent Boolean functions in compact form. For any Boolean function, its chain-reduced ZDD (CZDD) representation will be no larger than its ZDD representation, and at most twice the size of its BDD representation. The chain-reduced BDD (CBDD) of a function will be no larger than its BDD representation, and at most three times the size of its CZDD representation. Extensions to the standard algorithms for operating on BDDs and ZDDs enable them to operate on the chain-reduced versions. Experimental evaluations on representative benchmarks for encoding word lists, solving combinatorial problems, and operating on digital circuits indicate that chain reduction can provide significant benefits in terms of both memory and execution time

Editorial overview: Membrane traffic and cell polarity

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The significance of organic carbon and nutrient export from peatland-dominated landscapes subject to disturbance, a stoichiometric perspective

The terrestrial-aquatic interface is a crucial environment in which to consider the fate of exported terrestrial carbon in the aquatic system. Here the fate of dissolved organic carbon (DOC) may be controlled by nutrient availability. However, peat-dominated headwater catchments are normally of low nutrient status and thus there is little data on how DOC and nutrient export co-varies. We present nutrient and DOC data for two UK catchments dominated by peat headwaters. One, Whitelee, is undergoing development for Europe's largest windfarm. Glen Dye by comparison is relatively undisturbed. At both sites there are significant linear relationships between DOC and soluble reactive phosphorus and nitrate concentrations in the drainage waters. However, inter-catchment differences exist. Changes in the pattern of nutrient and carbon export at Whitelee reveal that landscape disturbance associated with windfarm development impacts the receiving waters, and that nutrient export does not increase in a stoichiometric manner that will promote increase in microbial biomass but rather supports aquatic respiration. In turn greater CO2 efflux may prevail. Hence disturbance of terrestrial carbon stores may impact the both the aquatic and gaseous carbon cycle. We suggest estimates of aquatic carbon export should inform the decision-making process prior to development in ecosystems and catchments with high terrestrial carbon storage

COMPARING THE PERFORMANCES OF THE PARTIAL EQUILIBRIUM AND TIME-SERIES APPROACHES TO HEDGING

This research compares partial equilibrium and statistical time-series approaches to hedging. The finance literature stresses the former approach, while the applied economics literature has focused on the latter. We compare the out-of-sample hedging effectiveness of the two approaches when hedging commodity price risk using a simple derivative with a linear payoff function (a futures contract). For various methods of parameter estimation and inference, we find that the partial equilibrium models cannot out-perform the time series model. The partial equilibrium models unpalatable assumptions of deterministically evolving futures volatility seems to impede their hedging effectiveness, even when potentially foresighted option-implied volatility term structures are employed.Marketing,

Estimating Actual Bid-Ask Spreads in Commodity Futures Markets

Various bid-ask spread estimators are applied to transaction data from LIFFE cocoa and coffee futures markets, and the resulting estimates are compared to observed actual bid-ask spreads. Results suggest that actual bid-ask spreads, which are not reported by most open-outcry futures markets, can be reasonably estimated using readily available transaction data. This is especially important since recent research seems to indicate that efforts to estimate effective spreads using data commonly available from futures markets have not been successful. Thus estimates of actual spreads can give market participants and researchers some idea of potential transaction costs. Accurate estimates of bid-ask spreads will also be needed to assess the relative efficiency of electronic versus open-outcry trading. Results indicate that estimators using averages of absolute price changes perform significantly better at estimating actual bid-ask spreads in futures markets than estimators using the covariance of successive price changes.Marketing,

PRICE AND PRICE RISK DYNAMICS IN BARGE AND OCEAN FREIGHT MARKETS AND THE EFFECTS ON COMMODITY TRADING

The effects of volatility of barge and ocean freight prices on prices throughout the international grain-marketing channel are analyzed using a Multivariate GARCH-M model. The model is used to infer the extent to which transportation price risk affects the level of international grain prices. Results indicate that both barge and ocean price volatility influence grain prices, but barge price volatility tends to have a greater impact on grain prices than that arising from ocean price volatility. The lack of a futures contract for barge rates may be partially responsible for its significant influence on grain price levels.Barge and ocean freight prices, futures contracts, Multivariate GARCH-Models, Price volatility, International Relations/Trade,

Studies in picosecond chronoscopy

Imperial Users onl

On Hamilton decompositions of infinite circulant graphs

The natural infinite analogue of a (finite) Hamilton cycle is a two-way-infinite Hamilton path (connected spanning 2-valent subgraph). Although it is known that every connected 2k-valent infinite circulant graph has a two-way-infinite Hamilton path, there exist many such graphs that do not have a decomposition into k edge-disjoint two-way-infinite Hamilton paths. This contrasts with the finite case where it is conjectured that every 2k-valent connected circulant graph has a decomposition into k edge-disjoint Hamilton cycles. We settle the problem of decomposing 2k-valent infinite circulant graphs into k edge-disjoint two-way-infinite Hamilton paths for k=2, in many cases when k=3, and in many other cases including where the connection set is ±{1,2,...,k} or ±{1,2,...,k - 1, 1,2,...,k + 1}