Numerical Exploration of the RI/MOM Scheme Gauge Dependence

The gauge dependence of some fermion bilinear RI/MOM renormalization constants is studied by comparing data which have been gauge-fixed in two different realizations of the Landau gauge and in a generic covariant gauge. The very good agreement between the various sets of results and the theory indicates that the numerical uncertainty induced by the lattice gauge-fixing procedure is below the statistical errors of our data sample which is of the order of (1-1.5)%.Comment: 3 pages, 2 figures, Lattice2002(theoretical

A possible theoretical explanation of metallicity gradients in elliptical galaxies

Models of chemical evolution of elliptical galaxies taking into account different escape velocities at different galactocentric radii are presented. As a consequence of this, the chemical evolution develops differently in different galactic regions; in particular, we find that the galactic wind, powered by supernovae (of type II and I) starts, under suitable conditions, in the outer regions and successively develops in the central ones. The rate of star formation (SFR) is assumed to stop after the onset of the galactic wind in each region. The main result found in the present work is that this mechanism is able to reproduce metallicity gradients, namely the gradients in the $Mg_2$ index, in good agreement with observational data. We also find that in order to honor the constant [Mg/Fe] ratio with galactocentric distance, as inferred from metallicity indices, a variable initial mass function as a function of galactocentric distance is required. This is only a suggestion since trends on abundances inferred just from metallicity indices are still uncertain.Comment: 18 pages, LaTeX file with 4 figures using mn.sty, submitted to MNRA

Logical Specification and Analysis of Fault Tolerant Systems through Partial Model Checking

This paper presents a framework for a logical characterisation of fault tolerance and its formal analysis based on partial model checking techniques. The framework requires a fault tolerant system to be modelled using a formal calculus, here the CCS process algebra. To this aim we propose a uniform modelling scheme in which to specify a formal model of the system, its failing behaviour and possibly its fault-recovering procedures. Once a formal model is provided into our scheme, fault tolerance - with respect to a given property - can be formalized as an equational µ-calculus formula. This formula expresses in a logic formalism, all the fault scenarios satisfying that fault tolerance property. Such a characterisation understands the analysis of fault tolerance as a form of analysis of open systems and thank to partial model checking strategies, it can be made independent on any particular fault assumption. Moreover this logical characterisation makes possible the fault-tolerance verification problem be expressed as a general µ-calculus validation problem, for solving which many theorem proof techniques and tools are available. We present several analysis methods showing the flexibility of our approach

The phase diagrams of iron-based superconductors: theory and experiments

Phase diagrams play a primary role in the understanding of materials properties. For iron-based superconductors (Fe-SC), the correct definition of their phase diagrams is crucial because of the close interplay between their crystallo-chemical and magnetic properties, on one side, and the possible coexistence of magnetism and superconductivity, on the other. The two most difficult issues for understanding the Fe-SC phase diagrams are: 1) the origin of the structural transformation taking place during cooling and its relationship with magnetism; 2) the correct description of the region where a crossover between the magnetic and superconducting electronic ground states takes place. Hence a proper and accurate definition of the structural, magnetic and electronic phase boundaries provides an extremely powerful tool for material scientists. For this reason, an exact definition of the thermodynamic phase fields characterizing the different structural and physical properties involved is needed, although it is not easy to obtain in many cases. Moreover, physical properties can often be strongly dependent on the occurrence of micro-structural and other local-scale features (lattice micro-strain, chemical fluctuations, domain walls, grain boundaries, defects), which, as a rule, are not described in a structural phase diagram. In this review, we critically summarize the results for the most studied 11-, 122- and 1111-type compound systems, providing a correlation between experimental evidence and theory

Linear feedback control of transient energy growth and control performance limitations in subcritical plane Poiseuille flow

Suppression of the transient energy growth in subcritical plane Poiseuille flow via feedback control is addressed. It is assumed that the time derivative of any of the velocity components can be imposed at the walls as control input, and that full-state information is available. We show that it is impossible to design a linear state-feedback controller that leads to a closed-loop flow system without transient energy growth. In a subsequent step, full-state feedback controllers -- directly targeting the transient growth mechanism -- are designed, using a procedure based on a Linear Matrix Inequalities approach. The performance of such controllers is analyzed first in the linear case, where comparison to previously proposed linear-quadratic optimal controllers is made; further, transition thresholds are evaluated via Direct Numerical Simulations of the controlled three-dimensional Poiseuille flow against different initial conditions of physical interest, employing different velocity components as wall actuation. The present controllers are effective in increasing the transition thresholds in closed loop, with varying degree of performance depending on the initial condition and the actuation component employed

Non-Perturbative Renormalisation of Composite Operators

It is shown that the renormalisation constants of two quark operators can be accurately determined (to a precision of a few per-cent using 18 gluon configurations) using Chiral Ward identities. A method for computing renormalisation constants of generic composite operators without the use of lattice perturbation theory is proposed.Comment: 3 pages, uuencoded compressed postscript file, to appear in the Proceedings of the International Symposium on Lattice Field Theory, Dallas, Texas, 12-17 October 1993, Southampton Preprint 93/94-0

Non-perturbative quark mass renormalization

We show that the renormalization factor relating the renormalization group invariant quark masses to the bare quark masses computed in lattice QCD can be determined non-perturbatively. The calculation is based on an extension of a finite-size technique previously employed to compute the running coupling in quenched QCD. As a by-product we obtain the $\Lambda$--parameter in this theory with completely controlled errors.Comment: Talk given at LATTICE '97, 6 pages, Latex source, 7 eps figures, needs epsfi

Non-perturbative improvement of composite operators with Wilson fermions

We propose a method to improve lattice operators composed of Wilson fermions which allows the removal of all corrections of $O(a)$, including those proportional to the quark mass, leaving only errors of $O(a^2)$. The method exploits the fact that chiral symmetry is restored at short distances. By imposing this requirement on correlation functions of improved lattice operators at short distances, the coefficients which appear in these operators can be determined. The method is an extension of the improvement program of the ALPHA collaboration, which, up to now, has only been applicable in the chiral limit. The extension to quarks with non-zero masses is particularly important for applications in heavy quark physics.Comment: 15 pages, Late

Non perturbative renormalization in coordinate space

We present an exploratory study of a gauge-invariant non-perturbative renormalization technique. The renormalization conditions are imposed on correlation functions of composite operators in coordinate space on the lattice. Numerical results for bilinears obtained with overlap and O(a)-improved Wilson fermions are presented. The measurement of the quark condensate is also discussed.Comment: Lattice2003(improve), 3 page

Effect of stress on protein homeostasis mediated by FKBP51 as a possible mechanism underlying stress-related disorders

Homeostasis is a dynamic equilibrium fundamental for a healthy system. A major challenge to homeostasis is environmental stress to which the organism reacts with the stress response. The hypothalamic-pituitary-adrenal (HPA) axis is the main regulator of the stress response that, upon activation, leads to the release of glucocorticoids (GCs). GCs are steroid hormones that exert their function via glucocorticoid receptors (GR). They trigger on one hand the appropriate stress response in the periphery, and, on the other, inhibit the HPA axis itself via negative feedback to restore homeostasis. FK506-binding protein 51 (FKBP51) is a co-chaperone able to modulate the GR, and therefore the HPA axis. Furthermore the expression of FKBP5, the gene coding for FKBP51, is induced by GR activation. In the last decade, increasing evidence has unveiled additional roles of FKBP51 in the regulation of several cellular pathways and functions that are independent from its inhibitory role on GR. Among these, FKBP51 has been shown to link stress signaling to macroautophagy, a lytic type of autophagy pathway. Autophagy represents one of the main mechanisms regulating cellular homeostasis and response to stress. For this reason, in the first part of this doctoral thesis, the role of GR-mediated stress was investigated on two further autophagic pathways: 1) the chaperone-mediated autophagy (CMA), a selective type of lytic autophagy, and 2) the secretory autophagy, an unconventional secretory mechanism regulated by autophagy-related proteins and found to be involved in extracellular signaling of immune response. For this aim, an in vitro approach was adopted using human and murine cell lines that were treated with dexamethasone (Dex), a synthetic GR agonist. For the first pathway, biochemical assays indicated that Dex-induced GR activation enhances CMA-mediated degradation of known CMA target proteins and that this process is dependent on FKBP51. Furthermore, the underlying molecular mechanism could be revealed by co-immunoprecipitation that displayed the co-localization of FKBP51, AKT and PHLPP on lysosomes. With a SILAC-based proteomics analysis, the proteome-wide effect of Dex-induced CMA could be observed and novel CMA targets were identified. For the second pathway, interactome and co-immunoprecipitation analyses revealed the involvement of FKBP51 in the SNARE complex assembly essential for secretory autophagy. Furthermore, treatment with Dex lead to a strengthened interaction between the SNARE proteins and FKBP51, and to an increased secretion of IL1B, a well characterized cargo of secretory autophagy, as observed with in vitro ELISA experiments and in vivo hippocampal microdialyses. A global effect of Dex-induced secretory autophagy was finally observed with a secretome analysis. The second part of my doctoral thesis focused on FKBP5/51 transcription variants and protein isoforms. In fact, despite its involvement in many cellular functions and disorders, very little is known about its four transcription variants and two isoforms. Thus, expression and degradation dynamics of FKBP51 isoforms and their differential functions in known molecular pathways were analyzed. Overall this study highlighted FKBP51 as crucial mediator of the stress response on two autophagic pathways, which might contribute to the regulation of cell and protein homeostasis. Furthermore, this regulatory mechanism might underlie the link of stress to immune and psychiatric disorders