Violation of the Bjorken Sum Rule in QCD

We show that the Bjorken sum rule for the first moment of the polarized nucleon structure function $g_1$ is not necessarily satisfied in QCD if the axial anomaly is taken into account. We argue that nonperturbative QCD effects should lead to a violation of the sum rule of the order of the percentage isospin violation in current quark masses.Comment: 11 pages, no figures (several typos and a numerical error on pag. 5 corrected

Loop corrections and graceful exit in string cosmology

We examine the effect of perturbative string loops on the cosmological pre-big-bang evolution. We study loop corrections derived from heterotic string theory compactified on a $Z_N$ orbifold and we consider the effect of the all-order loop corrections to the Kahler potential and of the corrections to gravitational couplings, including both threshold corrections and corrections due to the mixed Kahler-gravitational anomaly. We find that string loops can drive the evolution into the region of the parameter space where a graceful exit is in principle possible, and we find solutions that, in the string frame, connect smoothly the superinflationary pre-big-bang evolution to a phase where the curvature and the derivative of the dilaton are decreasing. We also find that at a critical coupling the loop corrections to the Kahler potential induce a ghost-like instability, i.e. the kinetic term of the dilaton vanishes. This is similar to what happens in Seiberg-Witten theory and signals the transition to a new regime where the light modes in the effective action are different and are related to the original ones by S-duality. In a string context, this means that we enter a D-brane dominated phase.Comment: 39 pages, Latex, 17 eps figure

Radiation test and application of FPGAs in the ATLAS Level 1 Trigger

The front-end system of the Silicon Drift Detectors (SDDs) of the ALICE experiment is made of two ASICs. The first chip performs the preamplification, temporary analogue storage and analogue-to-digital conversion of the detector signals. The second chip is a digital buffer that allows for a significant reduction of the connection from the front-end module to the outside world. In this paper, the results achieved on the first complete prototype of the front-end system for the SDDs of ALICE are presented

Causal Entropy Bound for Non-Singular Cosmologies

The conditions for validity of the Causal Entropy Bound (CEB) are verified in the context of non-singular cosmologies with classical sources. It is shown that they are the same conditions that were previously found to guarantee validity of the CEB: the energy density of each dynamical component of the cosmic fluid needs to be sub-Planckian and not too negative, and its equation of state needs to be causal. In the examples we consider, the CEB is able to discriminate cosmologies which suffer from potential physical problems more reliably than the energy conditions appearing in singularity theorems.Comment: 16 pages, no figures, acknowledgments adde

Anisotropic String Cosmology at Large Curvatures

We study the effect of the antisymmetric tensor field $B_{\mu\nu}$ on the large curvature phase of string cosmology. It is well-known that a non-vanishing value of $H=dB$ leads to an anisotropic expansion of the spatial dimensions. Correspondingly, in the string phase of the model, including $\alpha '$ corrections, we find anisotropic fixed points of the evolution, which act as regularizing attractors of the lowest order solutions. The attraction basin can also include isotropic initial conditions for the scale factors. We present explicit examples at order $\alpha '$ for different values of the number of spatial dimensions and for different ans\"{a}tze for $H$.Comment: 16 pages, Latex, 2 figure

Characterization of human frataxin missense variants in cancer tissues

Human frataxin is an iron binding protein involved in the mitochondrial Fe-S clusters assembly, a process fundamental for the functional activity of mitochondrial proteins. Decreased level of frataxin expression is associated with the neurodegenerative disease Friedreich ataxia. Defective function of frataxin may cause defects in mitochondria, leading to increased tumorigenesis. Tumour initiating cells show higher iron uptake, a decrease in iron storage and a reduced Fe-S clusters synthesis and utilization. In this study we selected, from COSMIC database, the somatic human frataxin missense variants found in cancer tissues p.D104G, p.A107V, p.F109L, p.Y123S, p.S161I, p.W173C, p.S181F, and p.S202F to analyze the effect of the single amino acid substitutions on frataxin structure, function and stability. The spectral properties, the thermodynamic and the kinetic stability, as well as the molecular dynamics of the frataxin missense variants found in cancer tissues point to local changes confined to the environment of the mutated residues. The global fold of the variants is not altered by the amino acid substitutions, however some of the variants show a decreased stability and a decreased functional activity in comparison to that of the wild type protein. This article is protected by copyright. All rights reserved