Nitrogen and phosphorus limitation of oceanic microbial growth during spring in the Gulf of Aqaba

Bioassay experiments were performed to identify how growth of key groups within the microbial community was simultaneously limited by nutrient (nitrogen and phosphorus) availability during spring in the Gulf of Aqaba's oceanic waters. Measurements of chlorophyll a (chl a) concentration and fast repetition rate (FRR) fluorescence generally demonstrated that growth of obligate phototrophic phytoplankton was co-limited by N and P and growth of facultative aerobic anoxygenic photoheterotropic (AAP) bacteria was limited by N. Phytoplankton exhibited an increase in chl a biomass over 24 to 48 h upon relief of nutrient limitation. This response coincided with an increase in photosystem II (PSII) photochemical efficiency (F v /F m), but was preceded (within 24 h) by a decrease in effective absorption crosssection (σPSII) and electron turnover time (τ). A similar response for τ and bacterio-chl a was observed for the AAPs. Consistent with the up-regulation of PSII activity with FRR fluorescence were observations of newly synthesized PSII reaction centers via low temperature (77K) fluorescence spectroscopy for addition of N (and N + P). Flow cytometry revealed that the chl a and thus FRR fluorescence responses were partly driven by the picophytoplankton (æ10 μm) community, and in particular Synechococcus. Productivity of obligate heterotrophic bacteria exhibited the greatest increase in response to a natural (deep water) treatment, but only a small increase in response to N and P addition, demonstrating the importance of additional substrates (most likely dissolved organic carbon) in moderating the heterotrophs. These data support previous observations that the microbial community response (autotrophy relative to heterotrophy) is critically dependent upon the nature of transient nutrient enrichment. © Inter-Research 2009

Research Library's Role and Place in the Educational Environment of Pedagogical University

The paper provides some results of the library reader survey which allowed establishing the new role and place of the research library of a pedagogical university. The creative role of the research library determines the possible options of interaction between the library and scientific and educational departments of the pedagogical university. In the educational environment, the library becomes a “third place” between home and classroom

Chance-Constrained Stochastic Programming for Integrated Services Network Management

this paper we formulate a model which aims to combine results on the probabilistic analysis of congestion in the network with optimisation of traffic routing decisions. The optimization model is essentially deterministic multicommodity network flow accounting for the stochasticity of traffic flows in the constraints. In this introduction a brief account of modern technology is given for the purpose of explaining the modelling assumptions. The derivation of a measure of stochastic multi-service traffic is presented in Section 2. Section 3 treats model formulation and implementation. Section 4 discusses model implementation and a simple numerical example. Conclusions and future research directions are contained in Section 5. Emerging from telephony, B-ISDN will carry different traffic such as voice, data and video over the same bearer. A standardised transport, multiplexing and switching technique called Asynchronous Transfer Mode (ATM) is recommended as a common digital format for implementing the B-ISDN concept. The resource model of an ATM network considers demands with very different statistical properties requiring flexible allocation of resources. For example data transmission services are highly bursty (burstiness = peak bit rate / average bit rate), whereas high definition television (HDTV) distribution has low burstiness but will consume a bit rate above 50 Mb/s per HDTV channel.All information coming from different traffic sources is transmitted by the means of short fixed length cells comprising a 5 byte header and a 48 byte information payload. The process of resource allocation in ATM networks exploits statistical multiplexing and is associated with some form of traffic usage contract. The notion of a committed quality or Grade of Service (GoS) per connection..

Research Papers

Risk management has often consisted of managing different types of risk separately as a consequence of the traditional internal bank organisation by asset class groups. However, the limitations of this segregated approach have increasingly become recognised, and many firms are now looking to use enterprise-wide risk management systems that integrate different types of risk into one framework. A framework underlying several models that measure the credit risk of a portfolio is extended in this paper to allow the integration of market risk and credit risk. Using a Monte Carlo methodology, the proposed integrated framework calculates a distribution for the value of a portfolio at a series of future time horizons. To reduce some of the data deficiencies that continue to be prevalent, particularly with the credit quality of firms, the proposed implementation of the framework uses market data where possible. Default probabilities are calculated using a structural model where some of the key parameters are estimated from equity data. As an illustration, the model developed in this paper is applied to a foreign exchange forward where there is a significant probability of default by the counterparty

Price Protection Strategies for an Oil Company

Crude oil price volatility has a significant impact on the planning decisions and budgets of oil companies. Taking account of such major activities as supply, storage, transformation and transportation together with trading on the commodity markets, we investigate the influence of random prices and demands. Such problems may be formulated as dynamic stochastic programmes with robust first stage solutions in the face of future price and demand uncertainties. In this paper we describe the trading environment and investigate hedging policies in coordination with the logistics planning problem

Extremes in operational risk management

Operational risk is defined as a consequence of critical contingencies most of which are quantitative in nature and many questions regarding economic capital allocation for operational risk continue to be open. Existing quantitative models that compute the value at risk for market and credit risk do not take into account operational risk. They also make various assumptions about ’normality ’ and so exclude extreme and rare events. In this paper we formalize the definition of operational risk and apply extreme value theory for the purpose of calculating the economic capital requirement against unexpected operational losses