Advection schemes for shelf sea models

Numerical models of shelf seas must handle sharp gradients in thermoclines and fronts, and at the edges of patches of passive tracer, often in the presence of strong tidal currents, without introducing excessive numerical diffusion or spurious oscillations. In a sigma coordinate model there is an additional problem, since then purely horizontal motion over a sloping sea bed may introduce strong numerical diffusion in the vertical, which can artificially erode thermoclines.In this paper, two advection schemes applicable to shelf sea models are examined. They are based on TVD (Total Variation Diminishing) and PPM (Piecewise Parabolic Method) techniques. They are demonstrated to give satisfactory performance for tracer advection in one, two and three dimensions. They are both monotonic, and the PPM scheme has particularly low numerical diffusion. In two and three dimensions directional splitting is used, which is handled by following advection with each horizontal velocity component by adjustment of the sigma levels in each water column using the same advection scheme. The artificial vertical diffusion is then small, particularly with PPM.The two schemes are also compared in a three-dimensional model of a cylindrical eddy of relatively fresh water, released from rest in an open sea region. Here, both salinity and momentum are advected. Laboratory experiments show that after an initial period of adjustment the eddy should become unstable, with a growth of cyclonic-anticyclonic eddy pairs. This is reproduced in the model, with the PPM scheme again producing sharper results than the TVD scheme.Integrated second moment calculations are used to compare the schemes. These demonstrate the lower numerical diffusion of the PPM scheme. This advantage is achieved at the cost of greater computing time.     

Aspects of family and kinship in a North Carolina coastal community: a comparative study

The almost total absence of social-science data on North Carolina coastal fishing communities has provoked this preliminary study of the role played by family and kinship ties among fishermen and boat builders in such a community, with a view to developing new fisheries management strategies from an assessment of the social and economic impacts of those which already exist.     

Can bus really be the new tram?

BRT appears to be less expensive to build and operate than tram systems but can it really approach the performance level of a tram system and what is the environmental performance of comparable systems?     

Natural Frequencies of Bernoulli-Euler Beams Resting on Two Elastic Supports: Application to Railway Vehicles

The purpose of the present study is to investigate the effect of the different parameters of the elastic supports upon which a deformable beam lies, upon the natural frequencies of the system.

The influence of support parameters is obtained by exploiting characteristic transcendental equations. The natural flexural vibrations of the beam are only affected by the stiffness of the supports over a very restricted range; outside this range the frequencies are those of a completely free beam or of a beam supported by two simple rigid supports (infinite stiffness).     

Freight forwarders speak: the preception of route comptetition via seaports in the European communities Research project —Part II

This paper, in two parts, reports on the perceptionof route competition via seaports in the European Communities Research Project wherein 72 interviews were held with freight forwarders throughout Europe (for the locations of the interviews see Part I, figure 1). This second part of the paper reports on the analysis of the openended tape-recorded responses of the interviewees to six separate sets of propositions they were shown; and there are extensive verbatim quotations. These quotations become longer as respondents warmed to the procedure. They tend to emphasize the increasing symbiosis of the land and sea operations within international transport. Among many vital topics of concern in a freight forwarder's life are costs and time. Not only does elapsed time equate with money expended, but also time limits equate with credit limits; any delay or unreliability results in sudden and enormous escalation of costs. Movement between countries in the mainland European Communities (EC) is more by truck than short-sea shipping. Customs are widely criticized as a cause of delays. The unfair (according to EC rules discrimination against UK forwarders by conferences tend to foster feeder services to mainland ports for British exports. But the opinion is that the power of conferences has declined markedly in recent years with the concomitant growth of independent lines. Freight forwarders may decline in numbers as their function changes. More capital is now required for computerizatio and credit bonds. There is a tendency to provide a more integrated service which would be symbolized by a growth of delivered price trading compared with free-on-board deliveries.     

Taxicab deregulation: Economic consequences and regulatory choices

The regulation of taxicab services is receiving an increasing amount of attention by city governments. At issue are the questions of whether local regulations should limit the supply of taxicabs and whether the regulations should control taxi fares.Recently, deregulation has become a popular suggestion; however, little empirical or theoretical evidence has existed to indicate the effects of taxi deregulations. This paper discusses these effects within a framework of eight regulatory scenarios involving different price, entry, and industry concentration factors. The analysis provides support for a public brokerage function.The preparation of this paper was supported, in part, by a contract from the Urban Mass Transportation Administration, U.S. Department of Transportation, Washington, DC.