The Effect of Periodic Silane Burst on the Properties of GaN on Si (111) Substrates

The periodic silane burst technique was employed during metalorganic chemical vapor deposition of epitaxial GaN on AlN buffer layers grown on Si (111). Periodic silicon delta doping during growth of both the AlN and GaN layers led to growth of GaN films with decreased tensile stresses and decreased threading dislocation densities, as well as films with improved quality as indicated by x-ray diffraction, micro-Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. The possible mechanism of the reduction of tensile stress and the dislocation density is discussed in the paper.

Effect of Gas Sparging in Mammalian Cell Bioreactors

One of the major problems in the operations of mammalian cell bioreactors is the detrimental effect of gas sparging. Since the most convenient way to oxygenate any bioreactor is by gas sparging, this adverse effect has often been one of the limiting oxygen transport problems in both laboratory and industrial mammalian cell bioreactors. When one examines the literature on the effect of gas sparging on the death of mammalian cells, a great deal of confusions has been reported. It is not clear from the published literature as to the leading cause for gas-sparged related cell death. These confusions prevent the rational design and operations of mammalian cell bioreactors. In our laboratory, we have attempted to address this problem both fundamentally as well as attempt to obtain a general understanding on the adverse effect of gas sparging. Our analyses first examined the fluid shear associated with the various sections that the gas bubbles encounter during entrance, passage through the bioreactor and the final exit of the gas bubbles. Our analyses showed that the major damage of the mammalian cells by gas bubbles is due to the burst of the bubbles when exiting the bioreactor. It was also our hypothesis that the entrained cells in the liquid boundary layer of the gas bubble upon bursting is the major cause for cell death. We have corroborated this hypothesis by correlating the liquid entrainment with the cell death rate using results from our laboratory as well as other studies. Pluonic F-68, a weak surfactant, has routinely been used in laboratory and industrial bioreactors. In the past, the protective effect of Pluronic F-68 has never been shown as to why it is effective. In our research, we have data using microphotography which clearly demonstrated and corroborated our entrainment hypothesis is the major reason for the effectiveness of Pluronic F-68 in protecting the cells from gas-sparged related cell death.

Whither Japan's Economy?

The Japanese economy entered a long recession in spring 1997. Its economic growth has been much lower than in the US and the EU despite large fiscal stimulus packages, a monetary policy which has brought interest rates to zero since 1999, injections of public money to recapitalize banks, and programs of liberalization and deregulation. How could all these policies have failed to bring the Japanese economy back on a sustainable growth path? This paper argues that the failure of Japan's efforts to restore a sound economic environment is the result of having deliberately chosen inappropriate and inadequate monetary and fiscal instruments to tackle the macroeconomic and structural problems that have burdened the Japanese economy since the burst of the financial bubble at the beginning of the 90s. These choices were deliberate, since the "right" policies (in primis the resolution of the banking crisis) presented unbearable political costs, not only for the ruling parties, but also for the bureaucratic and business elites. The misfortunes of the Japanese economy during the long recession not only allow us to draw important economic policy lessons, but also stimulate reflections on the disruptive role on economic policies caused by powerful vested interests when an economy needs broad and deep structural changes. The final part of the paper focuses on ways to tackle Japan's banking crisis. In particular, it explores the Scandinavian solution, which, mutatis mutandis, might serve Japanese policy-makers well.