Regional integration among developing countries : opportunities, obstacles and options.

Wirtschaftsunion; Entwicklungsländer;

The international competitiveness of developing countries for risk capital.

Direktinvestition; Investition; Entwicklungsländer;

The competitive strength of European, Japanese and US suppliers on ASEAN markets.

Internationaler Wettbewerb; Multinationales Unternehmen; Direktinvestition; Internationales Marketing; Firmeninterner Handel; Industriegüteraußenhandel; EU-Staaten; Japan; USA;

Effects of image charges, interfacial charge discreteness, and surface roughness on the zeta potential of spherical electric double layers

We investigate the effects of image charges, interfacial charge discreteness, and surface roughness on spherical electric double layers in electrolyte solutions with divalent counter-ions in the setting of the primitive model. By using Monte Carlo simulations and the image charge method, the zeta potential profile and the integrated charge distribution function are computed for varying surface charge strengths and salt concentrations. Systematic comparisons were carried out between three distinct models for interfacial charges: 1) SURF1 with uniform surface charges, 2) SURF2 with discrete point charges on the interface, and 3) SURF3 with discrete interfacial charges and finite excluded volume. By comparing the integrated charge distribution function (ICDF) and potential profile, we argue that the potential at the distance of one ion diameter from the macroion surface is a suitable location to define the zeta potential. In SURF2 model, we find that image charge effects strongly enhance charge inversion for monovalent interfacial charges, and strongly suppress charge inversion for multivalent interfacial charges. For SURF3, the image charge effect becomes much smaller. Finally, with image charges in action, we find that excluded volumes (in SURF3) suppress charge inversion for monovalent interfacial charges and enhance charge inversion for multivalent interfacial charges. Overall, our results demonstrate that all these aspects, i.e., image charges, interfacial charge discreteness, their excluding volumes have significant impacts on the zeta potential, and thus the structure of electric double layers.Comment: 11 pages, 10 figures, some errors are change

Semi-Active Magnetorheological Seat Suspensions for Enhanced Crashworthiness and Vibration Isolation of Rotorcraft Seats

This research focuses on the use of magnetorheological (MR) dampers for enhanced occupant protection during harsh vertical landings as well as isolation of the occupant from cockpit vibrations. The capabilities of the current state-of-the-art in helicopter crew seat energy absorption systems are highly limited because they cannot be optimally adapted to each individual crash scenario (i.e. variations in both occupant weight and crash load level). They also present an unnecessarily high risk of injury by not minimizing the load transmitted to the occupant during a crash. Additionally, current rotorcraft seats provide no means of isolating the occupant from harmful cockpit vibrations. The objective of this research was to investigate and demonstrate the feasibility and benefits of an MR-based suspension for rotorcraft seats. As such, this research began with an in-depth investigation into design feasibility. Three MR seat suspension design cases are investigated: 1) for only vibration isolation, 2) for adaptive occupant protection, and 3) for combined adaptive occupant protection and vibration isolation. It is shown that MR-based suspensions are feasible for each of these cases and the performance benefits and tradeoffs are discussed for each case. Next, to further illustrate the occupant protection benefits gained with an MR-based suspension, three control strategies were developed and performance metrics were compared. It was shown that MR dampers can be controlled such that they will automatically adapt to the crash load level as well as occupant weight. By using feedback of sensor signals, MR dampers were adjusted to utilize the full stroke capability of the seat suspension regardless crash level and occupant weight. The peak load transmitted to the occupant and the risk of spinal injury, therefore, was always minimized. Because this control significantly reduced or eliminated injury risk during less severe landings, it is a significant advance over the current state-of-the-art rotorcraft seat suspensions which can provide no better than 20% risk of occupant injury. Finally, an MR-based seat suspension designed solely for the purposes of vibration isolation was designed, analyzed, and experimentally demonstrated. MR dampers were integrated into the current crashworthy SH-60 crew seat with minimal weight impact such that the original crashworthy capabilities were maintained. Then, utilizing semi-active control, experimental vibration testing demonstrated that the system reduced vertical cockpit vibrations transmitted to the occupant by 76%. This is a significant advance over current state-of-the-art rotorcraft seats which provide no attenuation of cockpit vibrations

Induced Crystallization of Polyelectrolyte-Surfactant Complexes at the Gas-Water Interface

Synchrotron-X-ray and surface tension studies of a strong polyelectrolyte (PE) in the semi-dilute regime (~ 0.1M monomer-charges) with varying surfactant concentrations show that minute surfactant concentrations induce the formation of a PE-surfactant complex at the gas/solution interface. X-ray reflectivity and grazing angle X-ray diffraction (GIXD) provide detailed information of the top most layer, where it is found that the surfactant forms a two-dimensional liquid-like monolayer, with a noticeable disruption of the structure of water at the interface. With the addition of salt (NaCl) columnar-crystals with distorted-hexagonal symmetry are formed.Comment: 4 pages, 5 eps figure

Colloidal aggregation in microgravity by critical Casimir forces

By using the critical Casimir force, we study the attractive strength dependent aggregation of colloids with and without gravity by means of Near Field scattering. Significant differences were seen between microgravity and ground experiments, both in the structure of the formed fractal aggregates as well as the kinetics of growth. Ground measurements are severely affected by sedimentation resulting in reaction limited behavior. In microgravity, a purely diffusive behavior is seen reflected both in the measured fractal dimensions for the aggregates as well as the power law behavior in the rate of growth. Formed aggregates become more open as the attractive strength increases.Comment: 4 pages, 3 figure

A simulational and theoretical study of the spherical electrical double layer for a size-asymmetric electrolyte: the case of big coions

Monte Carlo simulations of a spherical macroion, surrounded by a size-asymmetric electrolyte in the primitive model, were performed. We considered 1:1 and 2:2 salts with a size ratio of 2 (i.e., with coions twice the size of counterions), for several surface charge densities of the macrosphere. The radial distribution functions, electrostatic potential at the Helmholtz surfaces, and integrated charge are reported. We compare these simulational data with original results obtained from the Ornstein-Zernike integral equation, supplemented by the hypernetted chain/hypernetted chain (HNC/HNC) and hypernetted chain/mean spherical approximation (HNC/MSA) closures, and with the corresponding calculations using the modified Gouy-Chapman and unequal-radius modified Gouy-Chapman theories. The HNC/HNC and HNC/MSA integral equations formalisms show good concordance with Monte Carlo "experiments", whereas the notable limitations of point-ion approaches are evidenced. Most importantly, the simulations confirm our previous theoretical predictions of the non-dominance of the counterions in the size-asymmetric spherical electrical double layer [J. Chem. Phys. 123, 034703 (2005)], the appearance of anomalous curvatures at the outer Helmholtz plane and the enhancement of charge reversal and screening at high colloidal surface charge densities due to the ionic size asymmetry.Comment: 11 pages, 7 figure

The electrical double layer for a fully asymmetric electrolyte around a spherical colloid: an integral equation study

The hypernetted chain/mean spherical approximation (HNC/MSA) integral equation is obtained and solved numerically for a totally asymmetric primitive model electrolyte around a spherical macroparticle. The ensuing radial distribution functions show a very good agreement when compared to our Monte Carlo and molecular dynamics simulations for spherical geometry and with respect to previous anisotropic reference HNC calculations in the planar limit. We report an analysis of the potential vs charge relationship, radial distribution functions, mean electrostatic potential and cumulative reduced charge for representative cases of 1:1 and 2:2 salts with a size asymmetry ratio of 2. Our results are collated with those of the Modified Gouy-Chapman (MGC) and unequal radius Modified Gouy-Chapman (URMGC) theories and with those of HNC/MSA in the restricted primitive model (RPM) to assess the importance of size asymmetry effects. One of the most striking characteristics found is that,\textit{contrary to the general belief}, away from the point of zero charge the properties of an asymmetric electrical double layer (EDL) are not those corresponding to a symmetric electrolyte with the size and charge of the counterion, i.e. \textit{counterions do not always dominate}. This behavior suggests the existence of a new phenomenology in the EDL that genuinely belongs to a more realistic size-asymmetric model where steric correlations are taken into account consistently. Such novel features can not be described by traditional mean field theories like MGC, URMGC or even by enhanced formalisms, like HNC/MSA, if they are based on the RPM.Comment: 29 pages, 13 figure