Growth and Melting of Metallic Nanoclusters in Glass: A Review of Recent Investigations

The mechanisms of nucleation and growth and the solid-to-liquid transition of metallic nanoclusters embedded in sodium borate glass were recently studied in situ via small-angle X-ray scattering (SAXS) and wide-an-le X-ray scattering (WAXS). SAXS results indicate that, under isothermal annealing conditions, the formation and growth of Bi or Ag nanoclusters embedded in sodium borate glass occurs through two successive stages after a short incubation period. The first stage is characterized by the nucleation and growth of spherical metal clusters promoted by the diffusion of Bi or Ag atoms through the initially supersaturated glass phase. The second stage is named the coarsening stage and occurs when the (Bi- or Ag-) doping level of the vitreous matrix is close to the equilibrium value. The experimental results demonstrated that, at advanced stages of the growth process, the time dependence of the average radius and density number of the clusters is in agreement with the classical Lifshitz-Slyozov-Waoner (LSW) theory. However, the radius distribution function is better described by a lognormal function than by the function derived from the theoretical LSW model. From the results of SAXS measurements at different temperatures, the activation energies for the diffusion of Ag and Bi through sodium borate glass were determined. In addition, via combination of the results of simultaneous WAXS and SAXS measurements at different temperatures, the crystallographic structure and the dependence of melting temperature T(m) on crystal radius R of Bi nanocrystals were established. The experimental results indicate that T(m) is a linear and decreasing function of nanocrystal reciprocal radius 1/R, in agreement with the Couchman and Jesser theoretical model. Finally, a weak contraction in the lattice parameters of Bi nanocrystals with respect to bulk crystals was established.

Growth of EuTe islands on SnTe by molecular beam epitaxy

Semiconductor magnetic quantum dots are very promising structures, with novel properties that find multiple applications in spintronic devices. EuTe is a wide gap semiconductor with NaCl structure, and strong magnetic moments S=7/2 at the half filled 4f(7) electronic levels. On the other hand, SnTe is a narrow gap semiconductor with the same crystal structure and 4% lattice mismatch with EuTe. In this work, we investigate the molecular beam epitaxial growth of EuTe on SnTe after the critical thickness for island formation is surpassed, as a previous step to the growth of organized magnetic quantum dots. The topology and strain state of EuTe islands were studied as a function of growth temperature and EuTe nominal layer thickness. Reflection high energy electron diffraction (RHEED) was used in-situ to monitor surface morphology and strain state. RHEED results were complemented and enriched with atomic force microscopy and grazing incidence X-ray diffraction measurements made at the XRD2 beamline of the Brazilian Synchrotron. EuTe islands of increasing height and diameter are obtained when the EuTe nominal thickness increases, with higher aspect ratio for the islands grown at lower temperatures. As the islands grow, a relaxation toward the EuTe bulk lattice parameter was observed. The relaxation process was partially reverted by the growth of the SnTe cap layer, vital to protect the EuTe islands from oxidation. A simple model is outlined to describe the distortions caused by the EuTe islands on the SnTe buffer and cap layers. The SnTe cap layers formed interesting plateau structures with easily controlled wall height, that could find applications as a template for future nanostructures growth. (C) 2010 Elsevier B.V. All rights reserved.

MODELING THE EVOLUTION OF COMPLEX NETWORKS THROUGH THE PATH-STAR TRANSFORMATION AND OPTIMAL MULTIVARIATE METHODS

The topology of real-world complex networks, such as in transportation and communication, is always changing with time. Such changes can arise not only as a natural consequence of their growth, but also due to major modi. cations in their intrinsic organization. For instance, the network of transportation routes between cities and towns ( hence locations) of a given country undergo a major change with the progressive implementation of commercial air transportation. While the locations could be originally interconnected through highways ( paths, giving rise to geographical networks), transportation between those sites progressively shifted or was complemented by air transportation, with scale free characteristics. In the present work we introduce the path-star transformation ( in its uniform and preferential versions) as a means to model such network transformations where paths give rise to stars of connectivity. It is also shown, through optimal multivariate statistical methods (i.e. canonical projections and maximum likelihood classification) that while the US highways network adheres closely to a geographical network model, its path-star transformation yields a network whose topological properties closely resembles those of the respective airport transportation network.

Influence of culture conditions on mycelial growth and bioluminescence of Gerronema viridilucens

Herein we describe a procedure for measuring the total light emission of the naturally bioluminescent tropical fungus Gerronema viridilucens and the optimization of culture conditions using multivariate factorial ANOVA. Cultures growing on an agar surface in 35 mm Petri dishes at 90% humidity show optimal bioluminescence emission at 25 degrees C in the presence of 1.0% sugar cane molasses, 0.10% yeast extract and pH 6.0 (nonbuffered). Temperature and pH are the most important factors for both mycelial growth and bioluminescence.

A note on policy, the composition of public expenditures and economic growth

In this article we study the growth and welfare effects of fiscal and monetary policies in economies where public investment is part of the productive process we present four different models that share the same technology with public infrastructure as a separate argument of the production function. We show that growth is maximized at positive levels of income tax and inflation. However, unless there are no transfers or public goods in the economy, maximization of growth does not imply welfare maximization we show that the optimal tax rate is greater than the rate that maximizes growth and the optimal rate of money creation is below the growth maximizing rate. With public infrastructure in the production function we no longer obtain superneutrality in the Sidrausky model.

Sustained growth, government expenditure and inflation

We construct and simulate a theoretical model in order to explain particular historical experiences in which inflation acceleration apparently helped to spur a period of economic growth. Government financed expenditures affect positively the produtivity growth in this model so that the distortionary effect of inflation tax is compensated by the productive effect of public expenditures. We show that for some interval of money creation rates there is an equilibrium where money is valued and where steady state physica1 capital grows with inflation. It is a1so shown that zero inflation and growth maximization are never the optimal policies.

A note on growth, welfare and public policy

In this note the growth anti welfare effects of fiscal anti monetary policies are investigated in three economies where public investment is part of the productive process It is shown that growth is maximized at positive levels of income tax and inflation but that there is no direct relationship between government size, productivity and growth or between inflation and growth. However, unless there are no transfers or public goods in the economy, maximization of growth does not imply welfare maximization and the optimal tax rate and government size are greater than those that maximize growth. Money is not superneutral anti the optimal rate of money creation is below the maximizing rate of growth.

A note on growth and inflation

A simple exercise on growth and inflationary financing of public expenditures is presented in this note. In a parameterized overlapping generations mode1 where government expenses positivc1y affects the growth rate of human capital, steady state capital and output increase with inflation, reproducing the so called Tobin effect. For large inflation rates, however, government authorities cannot affect real variables and there are only nominal effects. It is also shown that the optimal policy implies some inflation but not growth maximization.

Environmental protection and economic growth

This paper explores the link between environmental policy and economic growth by employing an extension of the AK Growth Model. We include a state equation for renewable natural resources. We assume that the change in environmental regulations induces costs and that economic agents also derive some utility from capital stock accumulation vis-`a-vis the environment. Using the Hopf bifurcation theorem, we show that cyclical environmental policy strategies are optimal, providing theoretical support for the Environmental Kuznets Curve.

Public versus private provision of infrastructure in a neoclassical growth model

This article studies the welfare and long run allocation impacts of privatization. There are two types of capital in this model economy, one private and the other initially public (“infrastructure”). A positive externality due to infrastructure capital is assumed, so that the government could improve upon decentralized allocations internalizing the externality, but public investmentis …nanced through distortionary taxation. It is shown that privatization is welfare-improving for a large set of economies and that after privatization under-investment is optimal. When operation inefficiency in the public sectoror subsidy to infrastructure accumulation are introduced, gains from privatization are higherand positive for most reasonable combinations of parameters.

Inflationary financing of public investment and economic growth

a theoretical model is constructed in order to explain particular historical experiences in which inflation acceleration apparently helped to spur a period of economic growth. Government financed expenditures affect positively the productivity growth in this model so that the distortionary effect of inflation tax is compensated by the productive effect of public expenditures. We show that for some interval of money creation rates there is an equilibrium where money is valued and where steady state physical capital grows with inflation. It is also shown that zero inflation and growth maximization are never the optimal policies.

Banks, liquidity crises and economic growth

How do the liquidity functions of banks affect investment and growth at different stages of economic development? How do financial fragility and the costs of banking crises evolve with the level of wealth of countries? We analyze these issues using an overlapping generations growth model where agents, who experience idiosyncratic liquidity shocks, can invest in a liquid storage technology or in a partially illiquid Cobb Douglas technology. By pooling liquidity risk, banks play a growth enhancing role in reducing inefficient liquidation of long term projects, but they may face liquidity crises associated with severe output losses. We show that middle income economies may find optimal to be exposed to liquidity crises, while poor and rich economies have more incentives to develop a fully covered banking system. Therefore, middle income economies could experience banking crises in the process of their development and, as they get richer, they eventually converge to a financially safe long run steady state. Finally, the model replicates the empirical fact of higher costs of banking crises for middle income economies.

Essays on economic growth

A fundamental question in development economics is why some economies are rich and others poor. To illustrate the income per capita gap across economies consider that the average gross domestic product (GDP) per capita of the richest 10 percent of economies in the year 2010 was a factor of 40-fold that of the poorest 10 percent of economies. In other words, the average person in a rich economy produces in just over 9 days what the average person in a poor economy produces in an entire year. What are the factors that can explain this difference in standard of living across the world today? With this in view, this dissertation is a conjunction of three essays on the economic growth field which we seek a possible responses to this question. The first essay investigates the existence of resource misallocation in the Brazilian manufacturing sector and measures possible distortions in it. Using a similar method of measurement to the one developed by Hsieh and Klenow (2009) and firm-level data for 1996-2011 we find evidence of misallocation in the manufacturing sector during the observed period. Moreover, our results show that misallocation has been growing since 2005, and it presents a non-smooth dynamic. Significantly, we find that the Brazilian manufacturing sector operates at about 50% of its efficient product. With this, if capital and labor were optimally reallocated between firms and sectors we would obtain an aggregate output growth of approximately 110-180% depending on the mode in which the capital share is measured. We also find that the economic crisis did not have a substantial effect on the total productivity factor or on the sector's misallocation. However, small firms in particular seem to be strongly affected in a global crisis. Furthermore, the effects described would be attenuated if we consider linkages and complementarity effects among sectors. Despite Brazil's well-known high tax burden, there is not evidence that this is the main source of resource misallocation. Moreover, there is a distinct pattern of structural change between the manufacturing sectors in industrialized countries and those in developing countries. Therefore, the second essay demonstrate that this pattern differs because there are some factors that distort the relative prices and also affect the output productivity. For this, we present a multi-sector model of economic growth, where distortions affect the relative prices and the allocation of inputs. This phenomenon imply that change of the production structure or perpetuation of the harmful structures to the growth rate of aggregate output. We also demonstrate that in an environment with majority decision, this distortion can be enhanced and depends on the initial distribution of firms. Furthermore, distortions in relative prices would lead to increases in the degree of misallocation of resources, and that imply that there are distinct patterns of structural changes between economies. Finally, the calibrated results of the framework developed here converge with the structural change observed in the firm-level data of the Brazilian manufacturing sector. Thereafter, using a cross-industry cross-country approach, the third essay investigates the existence of an optimal level of competition to enhance economic growth. With that in mind, we try to show that this optimal level is different from industrialized and under development economies due to the technology frontier distance, the terms of trade, and each economy's idiosyncratic characteristics. Therefore, the difference in competition industry-country level is a channel to explain the output for worker gap between countries. The theoretical and empirical results imply the existence of an inverted-U relationship between competition and growth: starting for an initially low level of competition, higher competition stimulates innovation and output growth; starting from a high initial level of competition, higher competition has a negative effect on innovation and output growth. Given on average industries in industrialized economies present higher competition level. With that if we control for the terms of trade and the industry-country fixed effect, if the industries of the developing economy operated under the same competition levels as of the industrialized ones, there is a potential increase of output of 0.2-1.0% per year. This effect on the output growth rate depends on the competition measurement used.

Debt and default in a growth model

This paper presents a small open economy model with capital accumulation and without commitment to repay debt. The optimal debt contract specifies debt relief following bad shocks and debt increase following good shocks and brings first order benefits if the country's borrowing constraint is binding. Countries with less capital (with higher marginal productivity of capital) have a higher debt-GDP ratio, are more likely to default on uncontingent bonds, require higher debt relief after bad shocks and pay a higher spread over treasury. Debt relief prescribed by the optimal contract following the interest rate hikes of 1980-81 is more than half of the debt forgiveness obtained by the main Latin American countries through the Brady agreements.

Use of Bioscreen C for growth of Mucor hiemalis in different carbon and nitrogen sources

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)