Operational Research and Corporate Planning in Railway Management

The current corporate planning process in Westrail is described and the roles played by operational research and mathematical modelling identified. They do not include forecasting the future. Instead of the "predict and prepare paradigm" a planning approach that tries to design the future has been adopted. The organisation is described in terms of how it has evolved, what it now is, and the key features of its environment. The three stages of planning are described-strategic, tactical and operational. These provide the means for management control of the railway. Environmental assessments linked to goal setting activities are incorporated within the planning process. The significance of operational research in planning, in particular mathematical modelling, is also described. Instead of finding problems to which existing techniques can be applied, O.R. is used to provide effective operational and planning systems as a means of assisting management to design the future for the organisation.     

On the economics of GPRS networks with Wi-Fi integration

Wi-Fi provides an appealing opportunity for GSM/GPRS operators to enhance their data capability. By integrating both networks, operators are able to provide 3G-like services. However, both networks have different data rates and capacity, which makes economics of the network integration and pricing of services a challenging issue. In this paper we introduce a novel pricing model for GPRS networks integrated with Wi-Fi networks. The model identifies how the integration can play a significant role in increasing operators’ overall revenue and potentially improve the performance of GPRS networks. We identify the optimal GPRS charging rate and Wi-Fi connection fee that yields maximum network revenue. In addition, we conduct a case study of a wireless operator that considers network integration, adopting our pricing model. The investment analysis provides the insightful information for profitable business cases of GPRS networks with Wi-Fi integration.     

Extraction of arsenic species from airborne particulate filters—Application to an industrial area of Greece

In the present study, the extraction of the arsenic species arsenite (As(III)), arsenate (As(V)), monomethyarsonic (MMA) and dimethylarsinic acid (DMA) from airborne particulate filters was investigated and optimized. For this purpose, total suspended particulate matter as well as size fractionated aerosol samples were collected from the industrial area of Aspropyrgos, Greece, in glass fibre and polycarbonated filters, respectively. Among H₃PO₄ and HCl, tested in various concentrations, concentrated HCl was found to be the most effective extractant for arsenic from both polycarbonated and glass fibre filters, without provoking any arsenic species transformation. However, the quantitative extraction of arsenic species from glass fibre filters required the subsequent washing of the filters with ultrapure water after their leaching with concentrated HCl. The developed procedure was applied to airborne particulate filters for arsenic speciation in Aspropyrgos' atmosphere. The results showed an enrichment of As in the fine (PM_2.5) compared with the coarse (PM_10–2.5) fraction of airborne particulates, while As(V) was found to be the predominant arsenic species in all samples. Finally, As concentration in the PM₁₀ fraction, for the investigated area and time period from December 2004 to June 2006, was below the target value of 6 ng As m^− 3, referred in the Directive 2004/107 of European Union.     

Comments on “The time evolution of the resistances andinductances of the discharges in a pulsed gas laser through its currentwaveforms” [and reply]

Persephonis et al. (see ibid., vol.24, p.1208-14 (1996)) present a method for calculating the time evolution of the resistance and inductance from the measured current and voltage waveforms of a circuit. As it was pointed out by Fridman (1997), from those measurements, it is impossible to obtain a unique time evolution of the resistance and inductance; further hypothesis are needed to solve the problem. In this comment we analyze the results presented in the above paper and find several contradictory features, like violations to the Kirchoff's law. Finally, we stress the fact that during the fast breakdown of a gas gap characterized by large, fast varying values of the resistivity, it is impossible to meaningfully and separately define a resistance and an inductance as lumped parameters of a circuit     

The effect of interfacial microstructure on the lipid oxidation stability of oil-in-water emulsions

Novel rattle-type magnetic mesoporous carbon spheres are successfully prepared using composite spheres with Fe(3)O(4) as core and mesoporous SiO(2) as shell plus solid SiO(2) as a middle layer as templates. These rattle-type spheres possess the magnetization strength of as high as 37.5 emu/g, high and tunable specific surface areas (382-512.6 m(2)/g) due to mesoporous carbon shells. This magnetic rattle-type structure and the readily accessible mesoporous shell are very favoring for the fast adsorption and release of guest objects triggered by external stimulus, for example, the spheres showed very good adsorptive property to dye.     

Augmented perpetual manifolds and perpetual mechanical systems-part II: theorem for dissipative mechanical systems behaving as perpetual machines of third kind

Perpetual points in mathematics defined recently, and their significance in nonlinear dynamics and their application in mechanical systems is currently ongoing research. The perpetual points significance relevant to mechanics so far is that they form the perpetual manifolds of rigid body motions of unforced mechanical systems, which lead to the definition of perpetual mechanical systems. The perpetual mechanical systems admit as perpetual points rigid body motions which are forming the perpetual manifolds. The concept of perpetual manifolds extended to the definition of augmented perpetual manifolds that an externally excited multi-degree of freedom mechanical system is moving as a rigid body, and may exhibit particle-wave motion. This article is complementary to the work done so far applied to natural perpetual dissipative mechanical systems with motion defined by the exact augmented perpetual manifolds, whereas the internal forces, and individual energies are examined, to understand further the mechanics of these systems while their motion is in the exact augmented perpetual manifolds. A theorem is proved stating that under conditions when the motion of a perpetual natural dissipative mechanical system is in the exact augmented perpetual manifolds, all the internal forces are zero, which is rather significant in the mechanics of these systems since the operation on augmented perpetual manifolds leads to zero internal degradation. Moreover, the theorem is stating that the potential energy is constant, and there is no dissipation of energy, therefore the process is internally isentropic, and there is no energy loss within the perpetual mechanical system. Also in this theorem is proved that the external work done is equal to the changes of the kinetic energy, therefore the motion in the exact augmented perpetual manifolds is driven only by the changes of the kinetic energy. This is also a significant outcome to understand the mechanics of perpetual mechanical systems while it is in particle-wave motion which is guided by kinetic energy changes. In the final statement of the theorem is stated and proved that the perpetual dissipative mechanical system can behave as a perpetual machine of third kind which is rather significant in mechanical engineering. Noting that the perpetual mechanical system apart of the augmented perpetual manifolds solutions is having other solutions too, e.g., in higher normal modes and in these solutions the theorem is not valid. The developed theory is applied in the only two possible configurations that a mechanical system can have. The first configuration is a perpetual mechanical system without any connection through structural elements with the environment. In the second configuration, the perpetual mechanical system is a subsystem, connected with structural elements with the environment. In both examples, the motion in the exact augmented perpetual manifolds is examined with the view of mechanics defined by the theorem, resulting in excellent agreement between theory and numerical simulations. The outcome of this article is significant in physics to understand the mechanics of the motion of perpetual mechanical systems in the exact augmented perpetual manifolds, which is described through the kinetic energy changes and this gives further insight into the mechanics of particle-wave motions. Also, in mechanical engineering the outcome of this article is significant, because it is shown that the motion of the perpetual mechanical systems in the exact augmented perpetual manifolds is the ultimate, in the sense that there are no internal forces which lead to degradation of the internal structural elements, and there is no energy loss due to dissipation.

     

Free-standing nanofibrous platinum sheets and their conductivity

Nanofibrous platinum sheets with a thickness of one to a few tens of nanometres were prepared over the submicron pores of polymer substrates by using long and rigid cadmium hydroxide nanostrands as templates, and these free-standing sheets gave metallic conductivity that varied greatly with the thickness.     

Stock market dynamics: Before and after stock market crashes

This paper presents a brief analysis on the distribution of magnitude of major stock market shocks. Based on the Gutenberg-Richter law in geophysics, we model the dynamics of market index returns prior and after major crashes in search of statistical regularities. For a large number of market crashes, our analysis suggests that the distribution of market volatility before and after the stock market crash is described well by the Gutenberg-Richter law, which reflects the scale-invariance and self-similarity of the underlying dynamics by a robust power-law relation. In addition, the rate of the decay of the aftershock sequence is well described by another power law, which is known as the Omori law. Power law relaxation seems to be a common behavior observed in complex systems such as the financial markets.