Atmospheric CO2 measurements and error analysis on seasonal air–sea CO2 fluxes in the Bay of Biscay

Atmospheric molar fraction of CO₂ (xCO₂^atm) measurements obtained on board of ships of opportunity are used to parameterize the seasonal cycle of atmospheric xCO₂ (xCO₂^atm) in three regions of the eastern North Atlantic (Galician and French offshore and Bay of Biscay). Three selection criteria are established to eliminate spurious values and identify xCO₂^atm data representative of atmospheric background values. The filtered data set is fitted to seasonal curve, consisting of an annual trend plus a seasonal cycle. Although the fitted curves are consistent with the seasonal evolution of xCO₂^atm data series from land meteorological stations, only ship-board measurements can report the presence of winter xCO₂^atm minimum on Bay of Biscay. Weekly air–sea CO₂ flux differences (mmol C·m^− 2 day^− 1) produced by the several options of xCO₂^atm usually used (ship-board measurements, data from land meteorological stations and annually averaged values) were calculated in Bay of Biscay throughout 2003. Flux error using fitted seasonal curve relative to on board measurements was minimal, whereas land stations and annual means yielded random (− 0.2 ± 0.3 mmol C·m^− 2·day^− 1) and systematic (− 0.1 ± 0.4 mmol C·m^− 2 day^− 1), respectively. The effect of different available sources of sea level pressure, wind speed and transfer velocity were also evaluated. Wind speed and transfer velocity parameters are found as the most critical choice in the estimate of CO₂ fluxes reaching a flux uncertainty of 7 mmol C·m^− 2·day^− 1 during springtime. The atmospheric pressure shows a notable relative effect during summertime although its influence is quantitatively slight on annual scale (0.3 ± 0.2 mmol C·m^− 2·day^− 1). All results confirms the role of the Bay of Biscay as CO₂ sink for the 2003 with an annual mean CO₂ flux around − 5 ± 5 mmol C m^− 2 day^− 1.     

Assimilation of buoy and satellite data in wave forecasts with integral control variables

The quality of numerical wave forecasts can be improved significantly by assimilating wave observations prior to the forecast. In the present study a technique for such assimilation is developed that exploits (a) the efficiency of a limited number of integral control variables, and (b) the effectiveness of variational (model-consistent) assimilation. The formal procedure is independent of the type of control variables and of the wave model (moreover, no adjoint wave model is required). In the present study, integral control variables are chosen to represent large-scale errors in the driving wind fields and uncertainties in the wave model. The assimilation technique is validated with observations of the ERS-1 satellite altimeter and two waverider buoys in two consecutive storms in the Norwegian Sea. The assimilation of the observations reduced the errors in the forecasted significant wave height at the buoy locations typically from 25% to 12%. For low-frequency waves the effect of the assimilation is similarly significant at one buoy location but marginal at the other buoy location.     

Stochastic modelling of quadratic wave components

This paper deals with stochastic wave models and their influence on wave load modelling of marine structures. The need for more refined theories is underlined for some applications and an entirely new quadratic model for the wave elevation is outlined. Finally, a number of physical phenomena relevant to waves are illustrated which are likely to be important for marine structures and could, in the near future, require ad hoc modelling.     

An operational tanker scheduling optimization system: background, current practice and model formulation

We describe the operational tanker scheduling problem in detail, as it relates to Chevron Shipping Company. We review the literature and current Chevron practice. We develop a model for the scheduling situation, and describe an integer programming formulation for schedule optimization, including the feasible schedule generation process, for a realistic representation of the company scheduling practices.     

Simulation‐based estimates of delays at freeway work zones

Work zone related traffic delay is an important cost component on freeways with maintenance activities. This study demonstrates that delays may be underestimated by using the deterministic queuing theory. Computer simulation is a valuable approach of estimating delay under a variety of existing and future conditions. However, a single simulation run, which can be quite costly in terms of both computer and analyst time, produces a delay estimate for only one traffic level under one set of conditions. A method is developed in this paper to approximate delays by integrating limited simulation data, obtained from CORSIM and the concept of deterministic queuing theory, while various geometric conditions and time‐varying traffic distribution are considered. A calibrated and validated simulation model that can reflect work zone traffic operations on a segment of Interstate 1–80 in New Jersey is used to generate data for developing the proposed model. The comparison of delays estimated by the deterministic queuing model and the proposed model is conducted, while factors affecting the accuracy of the delay estimates are discussed.     

CHARACTERISTICS OF ACTIONPOTENTIAL AND THEIR UNDERLYING OUTWARD CURRENTS IN MAMMALIAN TASTE RECEPTOR CELLS

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Modeling the bilateral micro‐searching behavior for urban taxi services using the absorbing markov chain approach

This paper develops a mathematical model that is based on the absorbing Markov chain approach to describe taxi movements, taking into account the stochastic searching processes of taxis in a network. The local searching behavior of taxis is specified by a logit form, and the O‐D demand of passengers is estimated as a logit model with a choice of taxi meeting point. The relationship between customer and taxi waiting times is modeled by a double‐ended queuing system. The problem is solved with a set of non‐linear equations, and some interesting results are presented. The research provides a novel and potentially useful formulation for describing the urban taxi services in a network.     

Model uncertainty and the management of a system of infrastructure facilities

The network-level infrastructure management problem involves selecting and scheduling maintenance, repair, and rehabilitation (MR&R) activities on networks of infrastructure facilities so as to maintain the level of service provided by the network in a cost-effective manner. This problem is frequently formulated as a Markov decision problem (MDP) solved via linear programming (LP). The conditions of facilities are represented by elements of discrete condition rating sets, and transition probabilities are employed to describe deterioration processes. Epistemic and parametric uncertainties not considered within the standard MDP/LP framework are associated with the transition probabilities used in infrastructure management optimization routines. This paper contrasts the expected costs incurred when model uncertainty is ignored with those incurred when this uncertainty is explicitly considered using robust optimization. A case study involving a network-level pavement management MDP/LP problem demonstrates how explicitly considering uncertainty may limit worst-case MR&R expenditures. The methods and results can also be used to identify the costs of uncertainty in transition probability matrices used in infrastructure management systems.     

DIETARY MAGNESIUM DEFICIENCY INCREASES LEVELS AND FUNCTION OF Giα IN THE RAT HEART AFTER MYOCARDIAL INFARCTION

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Bathymetric influences on the lower Chesapeake Bay hydrography

Observations of salinity and density in the lower Chesapeake Bay are used to describe the bathymetric influence on the transverse hydrographic structure in the area. Current velocity observations of high spatial resolution are also used to relate the flow structure to the hydrographic structure. Tidal flow characteristics in the lower bay are affected by the combination of bathymetry and hydrography. Increased stratification over channels relative to shoals may increase M₂ ellipticity with depth over channels but not over shoals. It is found that three consistent hydrographie features can be related to the transverse structure of the longitudinal flow: (1) persistent stratification over channels due to differential tidal advection of density gradients, (2) development of bottom front separating net inflows from net outflows at the region south of Chesapeake Channel, and (3) outflow of low salinity water at the northern end of a lower bay section. Based on these hydrographie features, two basic hydrographic regimes are proposed to exist throughout the year in the lower Chesapeake Bay: (1) a low buoyancy-high mixing energy regime of stratification restricted to channels, a northward monotonical increase in salinity, and a weak bottom front, and (2) a high buoyancy-weak mixing energy regime of stratified conditions everywhere, a large region of northward salinity decrease at the northern half of the section, and a robust bottom front. The dynamics in the transverse direction for the former regime is ageostrophic, and in the latter regime the contribution by geostrophy is approximately 50% as bathymetric influences become less evident.