Paul Christodoulides

Resonant capillary–gravity interfacial waves

Two-dimensional space-periodic capillary-gravity waves at the interface between two fluids of different densities are considered when the second harmonic and the fundamental mode are near resonance. A weakly nonlinear analysis provides the equations (normal form), correct to third order, that relate the wave frequency with the amplitudes of the fundamental mode and of the second harmonic for all waves with small energy. A study of the normal form for waves which are also periodic in time reveals three possible types of space- and time-periodic waves: the well-known travelling and standing waves as well as an unusual class of three-mode mixed waves. Mixed waves are found to provide a connection between standing and travelling waves

Antecedents and Consequences of an Eco-Friendly Export Marketing Strategy: The Moderating Role of Foreign Public Concern and Competitive Intensity

Despite growing concerns about environmental issues worldwide, research on the subject in the context of international marketing is virtually absent. The current study sheds light on the green aspects of exporting, using data collected from 216 exporting manufacturers. Drawing on the resource-based view and industrial organization theories, the authors show that certain organizational resources (i.e., financial, physical, and experiential) and capabilities (i.e., shared vision, cross-functional coordination, and technology sensing/response) are conducive to the deployment of an eco-friendly export marketing strategy (comprising product, price, distribution, and promotional elements). Such a strategy is more evident for exporters of industrial (vs. consumer) goods as well as for firms that sell to developed (vs. developing) countries. The results also suggest that the adoption of a green export marketing strategy has a positive effect on the firms export performance. In addition, the authors find that the strength of the link between eco-friendly export marketing strategy and export performance is positively moderated by foreign market environmental public concern and competitive intensity.

Stability of capillary–gravity interfacial waves between two bounded fluids

Two‐dimensional periodic capillary–gravity waves at the interface between two bounded fluids of different densities are considered. Based on a variational formulation, the relation between wave frequency and wave amplitude is obtained through a weakly nonlinear analysis. All classes of space‐periodic waves are studied: traveling and standing waves as well as a degenerate class of mixed waves. As opposed to water waves, mixed interfacial waves exist even for pure gravity waves. The stability of traveling and standing waves with respect to three‐dimensional modulations is then studied. By using the method of multiple scales, Davey–Stewartson‐type equations are obtained. A detailed stability analysis is performed in three cases: pure gravity waves, capillary–gravity waves when one layer is infinitely deep, and capillary–gravity waves when both layers are infinitely deep. The main results for oblique (i.e., combined longitudinal and transverse) modulations reveal a mostly stabilizing effect of the density rat...

Ideal jets falling under gravity

Steady two‐dimensional jets of an inviscid and incompressible fluid emerging from a nozzle and falling under gravity are calculated numerically by series truncation. The nozzle is aimed at an angle β above the horizontal. It is shown that there are flows for all values of β between 0° and 90° and for all values of the Froude number F. Local solutions are constructed to describe the limiting behavior of the flows as F→0 and as F→∞. The problem of a uniform free stream hitting a vertical wall, rising, and forming a jet that falls back upon the oncoming stream is also solved. It is shown that solutions exist only for Froude numbers greater than 2.96.

Despeckle Filtering Toolbox for Medical Ultrasound Video

Ultrasound medical video has the potential in differentiating between normal and abnormal tissue and structure. Ultrasound imaging is used in border identification and texture characterisation of the atherosclerotic carotid plaque in the common carotid artery CCA, the identification and measurement of the intima-media thickness IMT and the lumen diameter that are very important in the assessment of cardiovascular disease. However, visual perception is reduced by speckle noise affecting the quality of ultrasound B-mode imaging. Noise reduction is therefore essential for increasing the visual quality or as a pre-processing step for further automated analysis, such as the video segmentation of the IMT and the atherosclerotic carotid plaque in ultrasound video sequences. In order to facilitate this analysis, the authors have developed a video analysis software toolbox based on MATLAB® that uses video despeckling, texture analysis and image quality evaluation techniques to automate the pre-processing and complement the disease evaluation in ultrasound CCA videos. The proposed software, which is based on a graphical user interface GUI, incorporates video normalisation, 4 different despeckle filtering techniques DsFlsmv, DsFhmedian, DsFkuwahara and DsFsrad, 65 texture features, 11 quantitative video quality metrics and objective video quality evaluation. The software was validated on 10 ultrasound videos of the CCA, by comparing its results with quantitative visual analysis performed by two medical experts. It was shown that the filters DsFlsmv, and DsFhmedian improved video quality perception based on the experts assessment and the video quality metrics. It is anticipated that the system could help the physician in the assessment of cardiovascular video analysis. However, exhaustive evaluation of the despeckle filtering toolbox has to be carried out by more experts on more videos.

Spatial bifurcations of interfacial waves when the phase and group velocities are nearly equal

Steady waves at the interface between two immiscible and inviscid fluids of differing density are studied. The governing equations are reformulated as a spatial Hamiltonian system leading to new variational principles for uniform states and travelling waves. Analytical methods based on the properties of the Hamiltonian structure and numerical methods are used to find new branches of steady nonlinear interfacial waves in the neighbourhood of the singularity c = c g . The branches of travelling waves when plotted in (F, S)-space, where F and S are related to the energy flux and flow force respectively, show new bifurcations in the context of hydrodynamic waves even at very low amplitudes. The secondary bifurcations are explained by a spatial analogue of the superharmonic instability. An interesting analogy is also found between the spatial bifurcations of travelling waves and the Kelvin-Helmholtz instability. The new branches of waves occur at physically realizable values of the parameters and therefore could have implications for interfacial waves in applications.

Antecedents and consequences of infidelity in cross-border business relationships

The volatile, complex, and distant nature of the international business environment inevitably gives rise to incidences of infidelity among interacting exporters and importers. The authors propose and test a theoretically anchored model of the antecedents and consequences of infidelity in exporter–importer working relationships. The findings confirm that importers’ infidelity incidences occur more often in cases in which trust, satisfaction, commitment, and cooperation are low in the relationship. Indeed, the association between poor relationship quality and infidelity becomes stronger when the relationship is at a declining stage and is relatively young. The existence of infidelity in the relationship will lead to either punitive actions or reassessment measures on the part of the exporter, which are moderated by the degree of long-term orientation and social bonding that exists between the interacting parties.

Impact of a rising stream on a horizontal plate of finite extent

The steady flow of a stream emerging from a nozzle, hitting a horizontal plate and falling under gravity is considered. Depending on the length of the plate L and the Froude number F, the plate can either divert the stream or lead to its detachment. First, the problem is reformulated using conformal mappings. The resulting problem is then solved by a collocation Galerkin method; a particular form is assumed for the solution, and certain coefficients in that representation are then found numerically by satisfying Bernoullis equation on the free surfaces at certain discrete points. The resulting equations are solved by Newtons method, yielding various configurations of the solution based on the values of F and L. The lift exerted on the plate is computed and discussed. If the plate is long enough, physically meaningful solutions are found to exist only for values of F greater than or equal to a certain critical value F 0 , which is to be determined. Results are presented, both for F > F 0 where the detachment is horizontal and for F = F 0 where the detachment point is a stagnation point at a 120° corner. Related asymmetric flows where the rising stream is inclined are also studied.

Impact of a falling jet

Given the complexity of the problem of the impact of a mass of liquid on a solid structure, various simplified models have been introduced in order to obtain some insight on particular aspects of the problem. Here the steady flow of a jet falling from a vertical pipe, hitting a horizontal plate and flowing sideways is considered. Depending on the elevation H of the pipe relative to the horizontal plate and the Froude number F , the flow can either leave the pipe tangentially or detach from the edge of the pipe. When the flow leaves tangentially, it can either be diverted immediately by the plate or experience squeezing before being diverted. First, the problem is reformulated using conformal mappings. The resulting problem is then solved by a collocation Galerkin method; a particular form is assumed for the solution, and certain coefficients in that representation are then found numerically by satisfying Bernoullis equation on the free surfaces at certain discrete points. The resulting equations are solved by Newtons method, yielding various configurations of the solution based on the values of F and H . The pressure exerted on the plate is computed and discussed. For a fixed value of F , the maximum pressure along the plate goes through a minimum as H increases from small to large values. Results are presented for the three possible configurations: (i) tangential departure from the pipe and no squeezing, (ii) tangential departure from the pipe followed by squeezing of the liquid and (iii) detachment of the liquid from the pipe (with subsequent squeezing).

Global Warming: CO2 vs Sun

It is an undoubted fact, within the scientific community, that the global temperature has increased by about 0.7°C over the last century, a figure that is considered disproportionally large. With the whole world being alarmed, the scientific community has assumed the task to explain this warming phenomenon. This has resulted in the formation of basically two schools of thought with two opposing theories. The first theory (the most popular one) claims that the prime guilty for the recent temperature increase is the release of greenhouse gases – mainly Carbon Dioxide (CO2) – coming mostly from the burning of fossil fuels, the clearing of land and the manufacture of cement. Due to these anthropogenic activities the concentration of CO2 has increased by about 35% from its ‘pre-industrial’ values, with all the resulting consequences. There are though other factors – besides the greenhouse gases – that affect the global temperature, like changes in solar activity, cloud cover, ocean circulation and others. Therefore, the ‘second’ theory claims that it is the Sun’s activity that has caused the recent warming that, incidentally in this theory, is considered to be in the generally expected limits of the physical temperature variation throughout the aeons. One assumption on how the Sun is affecting the climate is that the magnetic field and the solar wind modulate the amount of high energy cosmic radiation that the earth receives. This in turn affects the low altitude cloud cover and the amount of water vapor in the atmosphere and thus regulates the climate. (It must be noted that water vapor is considered as the main greenhouse gas.) In the sequel both of the above-mentioned theories are examined and conclusions about their soundness are drawn. Firstly (section 2), an analysis in past time of the temperature of the Earth is presented, showing that today’s temperatures are not in any way extraordinary, unnatural or exceptional, contrary to what many scientists claim. In fact, on large time scale today’s temperatures agree with what was expected for this geologic period, while on a small time scale the higher temperatures observed are the result of a natural recovery of the planet from the global coldness of the Little Ice age. In section 3, the view of the Intergovernmental Panel on Climate Change (IPCC) on the effect of the accumulation of the CO2 in the atmosphere is presented. Then, in section 4 the CO2 accumulation effect during the past is examined on large and small time scales. Note that Florides & Christodoulides (2009) using three independent sets of data (collected from ice-cores and Chemistry) presented a specific regression analysis and concluded that forecasts about the correlation between CO2-concentration and temperature rely heavily on the choice of data used, making it very doubtful if such a correlation exists or even, if