Voltage rectification in two dimensional Josephson junction arrays

We study numerically the directed motion of vortices (antivortices) under an applied ac bias in two-dimensional Josephson junction arrays (JJA) with an asymmetrically modulated periodic vortex pinning potential. We find that the ratchet effect in large 2D JJA can be obtained using the RSJ model for the overdamped vortex dynamics. The rectification effect shows a strong dependence on vortex density as well as an inversion of the vortex flow direction with the ac amplitude, for a wide range of high magnetic field around f=1/2 (f being the vortex density). Our results are in good agreement with very recent experiments by D.E. Shalom and H. Pastoriza [Phys. Rev. Lett. 94, 177001, (2005)].Comment: 4 pages, 4 figures, Proceedings Vortex IV Conference, September 3-9, 2005, Crete, Greece. To appear in Physica

Regularity estimates for scalar conservation laws in one space dimension

In this paper we deal with the regularizing effect that, in a scalar conservation laws in one space dimension, the nonlinearity of the flux function $f$ has on the entropy solution. More precisely, if the set $\{w:f''(w)\ne 0\}$ is dense, the regularity of the solution can be expressed in terms of $\mathrm{BV}^\Phi$ spaces, where $\Phi$ depends on the nonlinearity of $f$. If moreover the set $\{w:f''(w)=0\}$ is finite, under the additional polynomial degeneracy condition at the inflection points, we prove that $f'\circ u(t)\in \mathrm{BV}_{\mathrm{loc}}(\mathrm{R})$ for every $t>0$ and that this can be improved to $\mathrm{SBV}_{\mathrm{loc}}(\mathbb{R})$ regularity except an at most countable set of singular times. Finally we present some examples that shows the sharpness of these results and counterexamples to related questions, namely regularity in the kinetic formulation and a property of the fractional BV spaces

Trade, technical progress and the environment: the role of a unilateral green tax on consumption

The paper proposes a two-country general equilibrium model of endogenous growth and trade between two regions, North and South, with different environmental standards. Pollution is a by-product of consumption and in order to abate it the northern region unilaterally imposes a green tax on consumption. As the tax affects domestic demand of consumer goods according to their pollution intensities, regardless of where those goods are produced, the model shows that such a unilateral environmental policy can increase the speed of technological change and pollution abatement in both regions.Trade, environment, consumption externality, technological change

The Pre--Main-Sequence of A-type stars

Young A-type stars in the pre--main-sequence (PMS) evolutionary phase are particularly interesting objects since they cover the mass range (1.5-4 solar ma sses) which is most sensitive to the internal conditions inherited during the protostellar phase. In particular, they undergo a process of thermal relaxation from which they emerge as fully radiative objects contracting towards the main sequence. A-type stars also show intense surface activity (including winds, accretion, pulsations) whose origin is still not completely understood, and infrared excesses related to the presence of circumstellar disks and envelopes. Disks display significant evolution in the dust properties, likely signalling the occurrence of protoplanetary growth. Finally, A-type stars are generally found in multiple systems and small aggregates of lower mass companions.Comment: 10 pages, 6 postscript figures, Proceedings of IAU Symp 224 (Poprad July 2004

Endogenous growth and trade liberalization between asymmetric countries

The paper presents a general equilibrium model of endogenous growth and trade between two countries, an advanced country (A) and a backward country (B). The development stage is summarized by the level of knowledge stock accumulated through R&D investments. The latter generates technological progress that intermediate goods producing firms, operating under increasing returns to scale and monopolistic competition, perform to obtain process innovations (reduction of production costs) when they are incumbents, or product innovations if they are new entrants. The model shows that convergence in long-run growth rates can be obtained even in absence of international technology spillover, in which case, under the assumption of no variety overlap, the gain from trade will be only static. Dynamic effects will be delivered instead in presence of an initial overlap in the varieties produced in the two countries, together with a wide gap in unit production costs. In this case it is shown that the impact of trade liberalization on firms profits might generate a cumulative causation process which may lead to a polarization of innovative productions in the advanced country.endogenous growth; trade liberalization; scale effect.

Environmental regulation and revealed comparative advantages in Europe: is China a pollution haven?

The relocation of more polluting industries in poorer countries due to gaps in environmental standards is known as the pollution haven effect, whereby the scale and the composition of output change across countries. Changes in the composition of the output mix might translate into changes of comparative advantages across countries, as revealed by trade flows. This paper focus on this issue and looks at the changes of bilateral revealed comparative advantages (RCAs) in the last decade between China and the major fourteen EU countries (EU14). Using industry level data on bilateral trade, air pollution, water pollution and several measures of environmental stringency, we find that, controlling for other factors that may have affected RCAs, such as labor costs, on average our EU14 countries have kept or improved their advantages with respect to China in both water polluting industries (such as paper and agro-based industries) and air polluting industries (such as basic metals and chemicals), while they have lost competitiveness in the more clean industries (such as machinery and fabricated metals).revealed comparative advantages, environmental regulation, industrial pollution

Bolivia during the global crisis 1998-2004: towards a ‘macroeconomics of microfinance

The macroeconomic role of microfinance appears to have varied enormously between country cases, as notably exposed by the recent wave of macro-economic crises. For example, in Indonesia in the late 1990s microfinance appears to have played a notably counter-cyclical role, whereas in Bolivia, the main focus of this paper, its role was in most cases to intensify rather than restrain the crisis. We find part of the explanation for this in the behaviour of government towards microfinance (much more conciliatory towards defaulting debtors in the Bolivian case) and in the structure of demand (unfavourable, in Bolivia, to the distribution and service sector which is the main market for microenterprise). However, closer examination of the Bolivian case suggests that institutional design also played an important role. In particular, those organisations which provided savings, training and quasi-insurance services bucked the trend of rising default rates and falling lending through the crisis and did particularly well, whereas the new breed of consumer-credit microfinance organisations did particularly badly and in several cases went out of business. This experience suggests,in particular, that it may be appropriate to call into question the fashionable´ minimalist´ (credit-only) model of microfinance, as certainly in Bolivia it was principally the credit-plus institutions which proved more financially disciplined and more resilient to crisis