Effects of poly(acrylic acid) and poly(ethylene oxide) adsorption on the stability of alumina suspension

The effect of adsorbed polymer on the stability of alumina suspension was investigated. Poly(ethylene oxide) (PEO), poly(acrylic acid) (PAA) and similar kinds of polymer salts were used as a dispersant. The amount of polymer adsorbed on alumina surface and the suspension stability was measured. The pH, molecular weight, and concentration were considered as experimental parameters. PEO shows low affinity on the alumina surface while PAA has high affinity. In the case of PAA adsorption, the surface charge change by polymer adsorption influences suspension stability strongly, but not in the case of PEO adsorption. In simultaneous adsorption of PEO and PAA, the PAA concentration was fixed and PEO concentration was varied. The stability of suspension increased with increasing PEO concentration, and this is partly due to the steric stabilization by adsorption of PAA-PEO complex or adsorption of PEO through pre-adsorbed PAA and the depletion effect of non-adsorbed polymer. Suspension adsorbing sodium salts of PAA and poly(methacrylic acid) (PMA) each showed similar stability. But, when the PEO and these kinds of salts were added together to the suspension, the one with PAA sodium salt could keep a higher stability even with lower molecular weights of PEO compared with suspension with PMA sodium salt.     

Cryptography during the French and American Wars in Vietnam

After Vietnam’s Declaration of Independence on 2 September 1945, the country had to suffer through two long, brutal wars, first against the French and then against the Americans, before finally becoming a unified country free of colonial domination in 1975. The authors’ purpose is to examine the role of cryptography in those two wars. Despite the far greater technological resources of their opponents, the communications intelligence specialists of the Vi?t Minh, the National Liberation Front, and the Democratic Republic of Vietnam had considerable success in both protecting Vietnamese communications and acquiring tactical and strategic secrets from the enemy. Perhaps surprisingly, in both wars there was a balance between the sides. Generally speaking, cryptographic knowledge and protocol design were at a high level at the central commands, but deployment for tactical communications in the field was difficult, and there were many failures on all sides.     

Optimal PN sequence design for quasisynchronous CDMA communicationsystems

Direct sequence (DS) code-division multiple-access (CDMA) is a modulation and multiple access technique currently being implemented in digital cellular mobile radio communication systems. The conventional quasisynchronous (QS) DS-CDMA communication system is generalized, and the problem of optimal spreading pseudonoise (PN) sequence design for new QS DS-CDMA communication systems is formulated. The classes of optimal PN sequences which have good pseudo-randomness and very small cross-correlation values for some range of offsets are designed by using a matrix-based approach. In contrast to the case of the other sequences, the optimal PN sequences produce small multiple-access interference (MAI) which is not affected by the number of users if there are sufficiently large number of users in the link. The new results are compared with the commonly used PN sequences to prove the superiority of our designed sequences, and the system performance of the QS-CDMA systems using different PN sequences are also evaluated     

Design of 24 GHz Radar with Subspace‐Based Digital Beam Forming for ACC Stop‐and‐Go System

For an adaptive cruise control (ACC) stop‐and‐go system in automotive applications, three radar sensors are needed because two 24 GHz short range radars are used for object detection in an adjacent lane, and one 77 GHz long‐range radar is used for object detection in the center lane. In this letter, we propose a single sensor‐based 24 GHz radar with a detection capability of up to 150 m and ±30° for an ACC stop‐and‐go system. The developed radar is highly integrated with a high gain patch antenna, four channel receivers with GaAs RF ICs, and back‐end processing board with subspace based digital beam forming algorithm.     

Characterization of the surface area of overflow droplets generated by a gas-lift pump under reduced pressure

Water-modelling experiments were carried out to characterize the surface area of overflow droplets generated by a gas-lift pump under reduced pressure as a function of various operating parameters, namely, top pressure, gas flow rate, nozzle submergence, lift ratio and riser diameter. The liquid phase mass transfer coefficient was obtained by applying the penetration theory (Treybal, 1980; Bird et al., 1960) to the overflow generated from the riser. Under reduced pressure, churn-turbulent flow, consisting of distorted bullet-shaped bubbles, was predominant in the flow regime. The increase of liquid circulation rate and flight time and the decrease of droplet size increased the refining rate. Because of the large droplet size, the refining rate of molten metals was smaller than that of water.     

An intra-industry trade model in a vertical differentiation framework

We developed a partial equilibrium model in which intra-industry trade arises as a result of utility maximization of consumers and profit maximization of firms. The driving force for intra-industry trade is non-homothetic preferences of consumers. We utilized a vertical differentiation framework, in which consumers have the same tastes for quality but different income levels determining their non-homogeneous choices. All firms in all countries have access to the same production technology, and there are no differences in factor endowments. Intra-industry trade arises as a result of each firm specializing on a certain segment of the market in all countries. We solved the model numerically for a two-country two-firm setup. In this setup, firms choose their product quality level and their price by maximizing their profits in a two-stage optimization problem. They also decide whether to export to the foreign market or to concentrate only on the domestic market in a standard two-by-two game. With introduction of non-zero transportation costs, trade volumes in both directions decrease. Transportation costs are shared between consumers and firms according to the marginal demand in the domestic versus in the foreign country. This model supports Krugman’s home market effect: In case of non-zero transportation costs, firms want to locate their production site in the country where there is higher marginal demand for their product.