The solution space of metabolic networks: producibility, robustness and fluctuations

Flux analysis is a class of constraint-based approaches to the study of biochemical reaction networks: they are based on determining the reaction flux configurations compatible with given stoichiometric and thermodynamic constraints. One of its main areas of application is the study of cellular metabolic networks. We briefly and selectively review the main approaches to this problem and then, building on recent work, we provide a characterization of the productive capabilities of the metabolic network of the bacterium E.coli in a specified growth medium in terms of the producible biochemical species. While a robust and physiologically meaningful production profile clearly emerges (including biomass components, biomass products, waste etc.), the underlying constraints still allow for significant fluctuations even in key metabolites like ATP and, as a consequence, apparently lay the ground for very different growth scenarios.Comment: 10 pages, prepared for the Proceedings of the International Workshop on Statistical-Mechanical Informatics, March 7-10, 2010, Kyoto, Japa

HT Camelopardalis: The simplest intermediate polar spin pulse

The intermediate polar HT Cam is unusual in that it shows no evidence for dense absorption in its spectrum. We analyse an XMM-Newton observation of this star, which confirms the absence of absorption and shows that the X-ray spin-pulse is energy independent. The modulation arises solely from occultation effects and can be reproduced by a simple geometrical model in which the lower accretion footprint is fainter than the upper one. We suggest that the lack of opacity in the accretion columns of HT Cam, and also of EX Hya and V1025 Cen, results from a low accretion rate owing to their being below the cataclysmic variable period gap.Comment: 5 pages, 6 figures, accepted for publication in MNRA

International financial flows, domestic banks, and the economic development of the periphery: Italy 1861-1913

This paper analyses the impact of different sources of financing (foreign capital, migrants’ remittances, and domestic banks intermediation) on economic development in Italy between 1861 and WWI. Existing literature has analysed the role of these channels of financial intermediation separately, while this paper for the first time considers them in conjunction. Using IRF from a Cholesky identification structure of a VAR model and relying on an original dataset that combines the most recent series of several financial and economic aggregates, this paper shows that both international capital and domestic saving had a significant impact on investment, while remittances did not. Foreign capital was invested directly, but also via domestic banks, in particular the “German-style” universal banks. Finally, foreign and d omestic capital had different attitudes towards the types of investment (construction vs. plant, machinery and transport equipment) and industries they financed. Combined together, these results shed a new light on the process of economic development of Italy and, more generally, of peripheral economies in the age of the international gold standard

Statistical mechanics of the mixed majority-minority game with random external information

We study the asymptotic macroscopic properties of the mixed majority-minority game, modeling a population in which two types of heterogeneous adaptive agents, namely ``fundamentalists'' driven by differentiation and ``trend-followers'' driven by imitation, interact. The presence of a fraction f of trend-followers is shown to induce (a) a significant loss of informational efficiency with respect to a pure minority game (in particular, an efficient, unpredictable phase exists only for f<1/2), and (b) a catastrophic increase of global fluctuations for f>1/2. We solve the model by means of an approximate static (replica) theory and by a direct dynamical (generating functional) technique. The two approaches coincide and match numerical results convincingly.Comment: 19 pages, 3 figure

Fungal environment in different rabbit intensive farms

Many environmental factors (for example, temperature, relative humidity, ventilation, NH3 concentration) can influence the health and welfare of rabbits reared in intensive farms. Among these elements, microorganisms and, in particular, fungi play a pivotal role in the spreading of potential pathogenic and zoonotic diseases. Aim of our work was to evaluate the fungal contamination in two different rabbit rearing (A and B). SAS System® (PBI International, Italy) and opened plates, filled with cultural media for fungal growth (environmental and dermatophytes) have been used. The data collected in both the farms showed that, for environmental fungi, Aspergillus, Alternaria and Penicillium were the most spread. On the contrary, for dermatophytes, there was a difference between farm A and B. In fact, in the first one Microsporum canis (a known zoonotic agent) has been recovered in high concentration, while in the second rearing we have isolated Microsporum gypseum a geophilic fungus with a very low pathogenic potential

Constraining the redshift evolution of the Cosmic Microwave Background black-body temperature with PLANCK data

We constrain the deviation of adiabatic evolution of the Universe using the data on the Cosmic Microwave Background (CMB) temperature anisotropies measured by the {\it Planck} satellite and a sample of 481 X-ray selected clusters with spectroscopically measured redshifts. To avoid antenna beam effects, we bring all the maps to the same resolution. We use a CMB template to subtract the cosmological signal while preserving the Thermal Sunyaev-Zeldovich (TSZ) anisotropies; next, we remove galactic foreground emissions around each cluster and we mask out all known point sources. If the CMB black-body temperature scales with redshift as $T(z)=T_0(1+z)^{1-\alpha}$, we constrain deviations of adiabatic evolution to be $\alpha=-0.007\pm 0.013$, consistent with the temperature-redshift relation of the standard cosmological model. This result could suffer from a potential bias $\delta\alpha$ associated with the CMB template, that we quantify it to be $|\delta\alpha|\le 0.02$ and with the same sign than the measured value of $\alpha$, but is free from those biases associated with using TSZ selected clusters; it represents the best constraint to date of the temperature-redshift relation of the Big-Bang model using only CMB data, confirming previous results.Comment: ApJ, in press. Manuscript matches the accepted version: 10 pages, 7 figures, 3 table

Mechanical Systems: Symmetry and Reduction

Reduction theory is concerned with mechanical systems with symmetries. It constructs a lower dimensional reduced space in which associated conservation laws are taken out and symmetries are \factored out" and studies the relation between the dynamics of the given system with the dynamics on the reduced space. This subject is important in many areas, such as stability of relative equilibria, geometric phases and integrable systems

Hubbard ladders in a magnetic field

The behavior of a two leg Hubbard ladder in the presence of a magnetic field is studied by means of Abelian bosonization. We predict the appearance of a new (doping dependent) plateau in the magnetization curve of a doped 2-leg spin ladder in a wide range of couplings. We also discuss the extension to N-leg Hubbard ladders