Cluster-cluster aggregation with particle replication and chemotaxy: a simple model for the growth of animal cells in culture

Aggregation of animal cells in culture comprises a series of motility, collision and adhesion processes of basic relevance for tissue engineering, bioseparations, oncology research and \textit{in vitro} drug testing. In the present paper, a cluster-cluster aggregation model with stochastic particle replication and chemotactically driven motility is investigated as a model for the growth of animal cells in culture. The focus is on the scaling laws governing the aggregation kinetics. Our simulations reveal that in the absence of chemotaxy the mean cluster size and the total number of clusters scale in time as stretched exponentials dependent on the particle replication rate. Also, the dynamical cluster size distribution functions are represented by a scaling relation in which the scaling function involves a stretched exponential of the time. The introduction of chemoattraction among the particles leads to distribution functions decaying as power laws with exponents that decrease in time. The fractal dimensions and size distributions of the simulated clusters are qualitatively discussed in terms of those determined experimentally for several normal and tumoral cell lines growing in culture. It is shown that particle replication and chemotaxy account for the simplest cluster size distributions of cellular aggregates observed in culture.Comment: 14 pages, 8 figures, to appear on Jsta

Bandwidth aspects in second generation current conveyors

This paper discusses bandwidth problems associated with second-generation current conveyors (CCII). In particular, our work is centered in high-capacitance applications, and has been oriented for wireless optical links and applied physics. We discuss techniques for improving bandwidth in these CCIIs, and develop a new CCII structure with larger bandwidth than traditional circuits. These circuits are then compared in terms of their noise and dynamic range characteristics. A test circuit was developed to verify these different bandwidth behaviors

Ab initio calculation of the dynamical properties of PPP and PPV

In this work, we have calculated the vibrational modes and frequencies of the crystalline PPP (in both the Pbam and Pnnm symmetries) and PPV (in the P21/c symmetry). Our results are in good agreement with the available experimental data. Also, we have calculated the temperature dependence of their specific heats at constant volume, and of their vibrational entropies. Based on our results, at high temperatures, the PPP is more stable in the Pnnm structure than in the Pbam one.Comment: 5 pages, 7 figures, accepted for publication in Braz. J. Phys., special number, Proceedings of BWSP-12, 12th Brazilian Workshop on Semiconductor Physic

DC magnetic field generation in unmagnetized shear flows

The generation of DC magnetic fields in unmagnetized plasmas with velocity shear is predicted for non relativistic and relativistic scenarios either due to thermal effects or due to the onset of the Kelvin-Helmholtz instability (KHI). A kinetic model describes the growth and the saturation of the DC field. The predictions of the theory are confirmed by multidimensional particle-in-cell simulations, demonstrating the formation of long lived magnetic fields ($t \sim 100s \omega_{pi}^{-1}$) along the full longitudinal extent of the shear layer, with transverse width on the electron length scale ($\sqrt{\gamma_0}c/\omega_{pe}$), reaching magnitudes $eB_{\mathrm{DC}}/m_ec\omega_{pe}\sim \beta_0\sqrt{\gamma_0}$

Targets and Inflation Dynamics

Brazil has experienced crucial changes in its inflation process since the adoption of inflation targeting in mid 1999. This article addresses changes in the analytical framework employed to track the inflation dynamics, specifically the relevance of an explicit target for inflation. A New-Keynesian Phillips curve (NKPC) is derived incorporating indexation not only to past inflation but also to inflation targets, generalizing the Woodford (2003) hybrid curve. In our modeling, firms that do not optimally set their prices in a given period adjust them only by indexing their previous prices to a weighted average of the inflation target and lagged inflation. In such a framework, the impact of inflation targets on agents' decisions regarding the supply side can be analytically measured by the parameter associated to the inflation target. It is shown that inflation target affects the welfare-based monetary policy objective function by penalizing deviations of actual inflation from target instead of from zero. This result establishes the micro foundation basis for ad-hoc loss functions as indicated in traditional literature. Therefore, the inflation target also affects the optimal target criterion. We also present a microfounded specification to model inflation expectations, and conclude that when firms attribute a high weight to the government's inflation target when setting their own prices, exchange rate and demand shocks are unable to alter significantly inflation expectations. Such a result gives some light to empirical ad hoc assessment conducted in traditional literature. Our empirical evidence shows that even after major shocks, the target ability of anchoring inflation has been restored. Although not formally tested, such a fact followed the monetary authorities' firm commitment to meet the inflation targets, reinforced by the government's necessary support through a consistent fiscal policy.

Is the New Resonance Spin 0 or 2? Taking a Step Forward in the Higgs Boson Discovery

The observation of a new boson of mass \sim 125\gev at the CERN LHC may finally have revealed the existence of a Higgs boson. Now we have the opportunity to scrutinize its properties, determining its quantum numbers and couplings to the standard model particles, in order to confirm or not its discovery. We show that by the end of the 8 TeV run, combining the entire data sets of ATLAS and CMS, it will be possible to discriminate between the following discovery alternatives: a scalar $J^P=0^+$ or a tensor $J^P=2^+$ particle with minimal couplings to photons, at a $5\sigma$ statistical confidence level at least, using only diphotons events. Our results are based on the calculation of a center-edge asymmetry measure of the reconstructed {\it sPlot} scattering polar angle of the diphotons. The results based on asymmetries are shown to be rather robust against systematic uncertainties with comparable discrimination power to a log likelihood ratio statistic.Comment: 11 pages, 6 figures, 1 table. References added, minor typos correcte