Ostracods from freshwater and brackish environments of the Carboniferous of the Midland Valley of Scotland : the early colonization of terrestrial water bodies

The Mississippian Strathclyde Group of the Midland Valley of Scotland yields some of the earliest non-marine ostracods. The succession records shallow marine, deltaic, estuarine, lagoonal, lacustrine, fluvial and swamp environments representing a series of staging-posts between fully marine and limnetic settings. Macrofossils and ostracods are assigned to marine, marginal marine, brackish and freshwater environments based on their faunal assemblage patterns. Key brackish to freshwater ostracods are Geisina arcuata, Paraparchites circularis n. sp., Shemonaella ornata n. sp. and Silenites sp. A, associated with the bivalves Anthraconaia, Carbonicola, Cardiopteridium, Curvirimula, Naiadites, the microconchid ‘Spirorbis’, Spinicaudata and fish. Many Platycopina and Paraparchiticopina ostracods are interpreted as euryhaline, which corresponds with their occurrence in marine to coastal plain water bodies, and supports the ‘estuary effect’ hypothesis of non-marine colonization. The success of non-marine colonization by ostracods was dependent on the intrinsic adaptations of ostracod species to lower salinities, such as new reproductive strategies and the timing of extrinsic mechanisms to drive non-marine colonization, such as sea-level change. The genus Carbonita is the oldest and most common freshwater ostracod, and went on to dominate freshwater environments in the Late Palaeozoic

Quantum Stabilizer Codes and Classical Linear Codes

We show that within any quantum stabilizer code there lurks a classical binary linear code with similar error-correcting capabilities, thereby demonstrating new connections between quantum codes and classical codes. Using this result -- which applies to degenerate as well as nondegenerate codes -- previously established necessary conditions for classical linear codes can be easily translated into necessary conditions for quantum stabilizer codes. Examples of specific consequences are: for a quantum channel subject to a delta-fraction of errors, the best asymptotic capacity attainable by any stabilizer code cannot exceed H(1/2 + sqrt(2*delta*(1-2*delta))); and, for the depolarizing channel with fidelity parameter delta, the best asymptotic capacity attainable by any stabilizer code cannot exceed 1-H(delta).Comment: 17 pages, ReVTeX, with two figure

Quantifying Bounded Rationality: Managerial Behaviour and the Smith Predictor

The concept of bounded rationality in decision making and research on its relegation to aggregate system dynamics is examined. By recasting one such example of a dynamic system, the Beer Game, as a Smith predictor control system is derived. A stability analysis is then employed to support the and qualify the assertion that the level of bounded rationality can adversely affect the aggregate dynamic behaviour of such supply chains. The analytical basis of these calculations enables the qualification of the potential cost improvements resulting from more desirable supply chain dynamics. This approach is designed to inform the strategic investment decision to purchase computational aids in order to overcome the level of bounded rationality in the system

The Stability of Supply Chains

A continuous time version of the well known beer game model is derived and its stability and robust stability properties are investigated. Novelty originates from the treatment of pure process delay rather than exponential lags and it is shown that this can lead to to diametrically different dynamics to the exponential lag case. The stability properties of the system are shown to support and quantify the qualitative empirical results of the beer game. Additional insight into the influence of certain model parameters is attained by the interpretation as the degree of mismatch in a Smith predictor regulator. The transient inability to supply all that is demanded is mimicked and shown to constitute an influential source of demand amplification. The analytical nature of these calculations engenders the capacity to improve supply chain dynamics through the synthesis and calibration of strategic supply chain trade off problems

Production-Inventory System Controller Design and Supply Chain Dynamics

This paper deals with the modelling and control of aggregated production-inventory systems as described by differential equations. Hitherto, research in this area has been characterised by the approximation of production delays, by first order lags, rather than more realistic pure delays. We demonstrate the substantial qualitative differences between these two approaches and thus generate the motivation for the rest of the paper, which tackles pure delay systems. The application of some relatively new design methodologies for delay systems yields four design choices, which are tested for their performance over a range of criteria including stability robustness. The investigation is then extended to the model of a supply chain comprising many such production-inventory systems. The mechanism by which disturbances can be transmitted along the supply chain causing disruption and incurring costs to other supply chain echelons is elucidated. An heuristic feedback policy designed to adaptively tune the individual system designs in response to such disturbances is presented

The Optimal Control of Inventory Systems

The science of Operational Research has traditionally dominated in the field of inventory theory. Yet there have been sporadic attempts to apply methods from control theory in this domain. We review these efforts, concentrating particularly on optimal control approaches. We also enumerate the generic benefits and limitations of operational research methods. Through these efforts we judge whether the supremacy of operational research techniques in the field of inventory systems is warranted. We apply a novel optimal control algorithm to a differential equation model of an inventory system. This enables us to mimic the cost structures implied by quantity discounts and approximate capacity constraints. Some examples illustrate how optimal responses to instantaneous jumps in demand are generated and how these are affected by quantity discounts

Quantum key distribution without alternative measurements

Entanglement swapping between Einstein-Podolsky-Rosen (EPR) pairs can be used to generate the same sequence of random bits in two remote places. A quantum key distribution protocol based on this idea is described. The scheme exhibits the following features. (a) It does not require that Alice and Bob choose between alternative measurements, therefore improving the rate of generated bits by transmitted qubit. (b) It allows Alice and Bob to generate a key of arbitrary length using a single quantum system (three EPR pairs), instead of a long sequence of them. (c) Detecting Eve requires the comparison of fewer bits. (d) Entanglement is an essential ingredient. The scheme assumes reliable measurements of the Bell operator.Comment: REVTeX, 5 pages, 2 figures. Published version with some comment

Entanglement can increase asymptotic rates of zero-error classical communication over classical channels

It is known that the number of different classical messages which can be communicated with a single use of a classical channel with zero probability of decoding error can sometimes be increased by using entanglement shared between sender and receiver. It has been an open question to determine whether entanglement can ever increase the zero-error communication rates achievable in the limit of many channel uses. In this paper we show, by explicit examples, that entanglement can indeed increase asymptotic zero-error capacity, even to the extent that it is equal to the normal capacity of the channel. Interestingly, our examples are based on the exceptional simple root systems E7 and E8.Comment: 14 pages, 2 figur

Modelling the Dynamics of Supply Chains

Since the 1960's many academic and managerial researches have focused their attention on production-inventory-distribution systems. The application of diverse mathematical techniques from continuous differential equation systems to mathematical programming models have been attempted. Yet none have predominated over Operational Research techniques either in industry or the research literature. This aper aims to enumerate and appraise the various methodologies which have been applied to supply chain analysis over the last forty years. In particular we shall ask of each technique: To what extent does it reveal the dynamics of the process involved? These questions are important since only through knowledge of the dynamics can we gain a full appreciation and understanding of the factors which affect supply chain performance

The Effect of Batched Production on Demand Amplification

Demand amplification is the tendency of small fluctuations in demand at the retailer end of the supply chain to be amplified as they are communicated down the chain. A brief review of the literature on this phenomenon is presented, concentrating particularly on the causes propounded. A continuous-time differential equation model of a production-inventory system is then proposed. The application of a novel optimal control algorithm is applied in order to simulate the rational behaviour of inventory managers. This algorithm allows us to mimic the discontinuous cost structures implied by the advantages of batched production. By simulating the response of the system to small changes in demand, the relationship between batch size and the magnitude of demand amplification is investigated