A summary of the formation and seasonal progression of the Northeast Water Polynya

A summary of the seasonal development of the Northeast Water Polynya ice cover characteristics is presented. This is based primarily on satellite remote sensing observations, with some in situ measurements, including both new and published data.     

The Dead Sea hydrography from 1992 to 2000

The modern hydrological regime of the Dead Sea is strongly affected by anthropogenic activity. The natural fresh water budget has changed mainly due to the drastic reduction of runoff. Since 1977, the surface level of the Dead Sea has been lowered by an average rate of about 60 cm/year and for the period from 1998 to 2000, the lowering rate has reached about 100 cm/year. As a result of the runoff reduction, the upper layer salinity of the Dead Sea has increased and the gravitational stability of the water body was diminished. Eventually, during the winter of 1978–1979, the lake waters overturned, bringing to an end the long-term stable meromictic¹ hydrological regime. The lake entered a new phase in which its hydrological regime switches between holomictic and meromictic regimes, depending on the size of the runoff into the lake (i.e. the amount of precipitation in the lake's watershed). The first holomictic period, 1979–1980, lasted for 2 months only. It was succeeded by a 4-year meromictic period (1980–1983). The second holomictic period lasted for 9 years (1983–1991). The rainy winter of 1991–1992 resulted in an almost 2-m sea level rise. The upper layer with a relatively low salinity was restored and a new meromictic period persisted for 4 years, until winter 1995–1996. During the last meromictic period, the hydrological regime of the Dead Sea was characterized by following long-term trends: the depth of the summer thermocline increased from 12–15 to 25–30 m; the quasi-salinity of the upper layer, initially of about 164 kg/m³, increased rapidly at a rate of about 16–18 kg/m³/year; the quasi-salinity of the deep water, initially of about 235 kg/m³, decreased slowly at a rate of about 0.08–0.10 kg/m³/year (for the sake of comparison, a quasi salinity of 235 kg/m³ is the equivalent of 280‰ “usual” salinity); and the winter minimal temperature of the upper layer, initially of about 16 °C, increased rapidly at a rate of about 2 °C/year. In November 1995, the latest meromictic period of the Dead Sea came to an end. During the present holomictic period, 1996–2000, the hydrological regime of the Dead Sea is also characterized by long-term trends: the quasi-salinity of the entire Dead Sea increased at a rate of about 0.5 kg/m³/year, with practically no decrease during the winters; the temperature of the deep water mass increased with a rate of about 0.25 °C/year; and the period of vertical convection of the entire water column, initially about 3 months, increased at a rate of about 1 week/year. Moreover, we observed that the temperature and salinity of the bottom layer in the deepest part of the Dead Sea raised by about 0.5–0.6 °C and 0.15–0.25 kg/m³ during each holomictic summer.     

The Force-Angle Measure of Tipover Stability Margin for Mobile Manipulators

Mobile manipulators operating in field environments will be required to apply large forces, or manipulate large loads, and to perform such tasks on uneven terrain which may cause the system to approach, or reach, a dangerous tipover instability. To avoid tipover in an automatic system, or to provide a human operator with an indication of proximity to tipover, it is necessary to define a measure of available stability margin. This work presents a new tipover stability measure (the Force-Angle stability measure) which has a simple geometric interpretation, is easily computed, and is sensitive to changes in Center of Mass height. The proposed metric is applicable to systems subject to inertial and external forces, operating over even or uneven terrains. Requirements for computation and implementation of the measure are described, and several different categories of application of the measure are presented along with useful normalizations. Performance of the Force-Angle measure is demonstrated and compared with that of other stability margin measures using a forestry vehicle simulation. Results show the importance of considering both center-of-mass height and system heaviness, and confirm the effectiveness of the Force-Angle measure in monitoring the tipover stability margin.     

Geometric modelling of bulbous bows with the use of non-uniform rational B-spline surfaces

Nowadays, bulbous bow forms have become a common design feature in most conventional ship designs. The design of a bulbous bow is usually attempted with the use of certain form parameters that are imposed using the designer's experience or regression values that provide the optimum parameters based on experimental tests or computational fluid dynamics (CFD) calculations. In this article, the geometric modelling of a bulbous bow form that complies with a series of parameters is presented. First, a wire model was constructed with cubic B-spline curves that hold certain form parameters that the designer wants to impose. Second, a B-spline surface that fits these splines was mathematically constructed. A review of the influence of the design parameters used on the bulbous bow properties was made. This method could be used prior to numerical optimization of a bulbous bow because different variations of the design can be easily generated. These variations can be tested numerically using CFD software. A practical application example of the method is shown.     

A study of the response of chlorophyll-a biomass to a winter upwelling event off Western Iberia using SeaWiFS and in situ data

Observations of a winter upwelling event off Western Iberia shelf/slope in the area of influence of the Western Iberia Buoyant Plume (WIBP) were conducted in February 2000. Spatial patterns and time evolution of the chlorophyll-a (chl-a) biomass are analysed, based on in situ and satellite data. SeaWiFS-derived chl-a concentration L2 products were used to track the chlorophyll front and estimate its westward migration velocity (maximum up to 29 km day⁻¹), as well as to characterize the frontal system and its evolution. A method associating the type of spectral signature of a pixel to the fraction of chlorophyll probed by SeaWiFS enabled the estimation of the chl-a biomass within error intervals. High chlorophyll concentrations (for wintertime) were observed over the shelf and slope, up to large distances to the coast. Due to the WIBP, a shallow Ekman layer developed, being nearly coincident with the stratified upper meters. The transport comprised westward advection and stretching of the plume, with little entrainment with the offshore deep mixed layer waters. The relative enlargement of the total area of the Inside-Front Zone (IFZ) during the upwelling event was roughly accompanied by the maintenance of the average biomass per unit of area, considering the water column up to depths of interest. This suggests that there was a net increase of chl-a biomass inside the water column associated with the IFZ, roughly proportional to the increase in the IFZ area. Retention of phytoplankton in the shallow stratified nutrient-rich waters of the WIBP was a key factor for this increase in chl-a biomass.     

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.     

An automatic segmentation procedure for studying variations in mode choice behaviour

Urban areas are very complex and heterogeneous in terms of their population composition and activity systems. The transport system, modal choices and service levels available to the population also varies considerably across space and time. These similarities and differences in choices and levels of explanatory variables facing individual tripmakers have to be explicitly considered in any study of transport behvior. The common practice has been to include user attributes, in addition to the system characteristics, in the modal utility functions to help capture differences in choice behavior across individuals. However, it could well be that the mode-choice behavior of a segment of the population is fundamentally different from other segments of the population. In view of this, some studies have applied segmentation schemes to help identify the subgroups of presumably different travel responses. Typically, such schemes have been based on stratification of the population by a single variable, chosen either based on a priori notions or one-way cross tabulations. These have their shortcomings. Thus, this paper develops an analytical procedure that simultaneously deals with level of service, socioeconomic and spatial factors to determine the relative role each plays in determining travel behavior. The procedure is applied to data from the Toronto region to illustrate its use.     

Some properties of international maritime statistics

This paper tests two fundamental hypotheses concerning international maritime statistics. The first one deals with the question of stationary of the maritime market statistics. The second hypothesis tested is the assumption that the international maritime statistical time series are not distributed according to a normal of Guassian probability law, but rather belong to the same family of distributions with distinctly different critical parameters. Through well documented statistical methods, the paper concludes that the international freight rates observed on a day to day basis are generated by a random walk process. The paper finds that the shipping industry's conventioal wisdom is essentially correct. 'Last done' is as good a forecast of tomorrow's freight rate as any other generated by more sophisticated forecasting methods. Furthermore, freight rates and secondhand tonnage prices fluctuate closely together. The freight rates are generated by stochastic processes fully described by the Paretian family of distributions. The critical parameters of these distribution, the characteristic exponents, are such that the risk conscious ship operator can indeed reduce his exposure to risk by securing a correct set of freight rate contracts.     

A comparison between conventional and advanced handling systems for low volume container maritime terminals

In this paper a conventional low volume maritime terminal equipped with straddle carriers is compared against an advanced automatic stacking crane/automatic guided vehicle alternative. For both configurations a convenient layout was designed, a reasonable level of service (common for both terminals) was adopted, and the required amount of equipment was determined using computer simulation. The results indicate that the total cost per container and the area requirements do not differ considerably between the two configurations although there exist differences in the investment capital and the personnel required.