1,354,247 research outputs found
Should aid reward good outcomes? Optimal contracts in a repeated moral hazard model of foreign aid allocation
No full textWe consider in this paper a repeated moral hazard model where a donor, characterized both by altruistic and non altruistic motives, finances a three periods poverty eradication project. In order to model the significant problems that donors face in the actual implementation of aid programs, we assume that the elites of the recipient country, who play an important role in carrying out the project, have an incentive to divert resources from the intended use. We show that optimal aid contracts should be conditional on the previous results of the project. We distinguish however between strong conditionality where contracts are specified on the basis of the performance of the project in all periods and weak conditionality where contracts have, instead, short memory. In this case a recipient that experienced a negative performance will receive less aid in the following period, but will bear no further consequences in the future. If a donor assigns a lot of weight to the welfare of the recipient country compared to the cost of giving aid and the incentive of the elite to divert resources, an optimal aid allocation policy always implies a positive level of aid even if the project had a negative outcome in the previous period. In the opposite case, optimal contracts imply no aid after a negative performance of the projec
Recursive integral equations with positive kernel for lattice calculations
No full textWe derive a Kirkwood-Salzburg integral equation, with positive defined kernel, for the states of lattice models of statistical mechanics and quantum field theory. The equation is defined in the thermodynamic limit, and its iterative solution is convergent; moreover, positivity leads to an exact a priori bound on the iteration. The equation's relevance as a reliable algorithm for lattice calculations is therefore suggested, and it is illustrated with a simple application. It should provide a viable alternative to Monte Carlo methods for models of statistical mechanics and lattice gauge theories
Pin1 and neurodegeneration: a new player for prion disorders?
No full textPin1 is a peptidyl-prolyl isomerase that catalyzes the cis/trans conversion of phosphorylated proteins at serine or threonine residues which precede a proline. The peptidyl-prolyl isomerization induces a conformational change of the proteins involved in cell signaling process. Pin1 dysregulation has been associated with some neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease and Huntington's disease. Proline-directed phosphorylation is a common regulator of these pathologies and a recent work showed that it is also involved in prion disorders. In fact, prion protein phosphorylation at the Ser-43-Pro motif induces prion protein conversion into a disease-associated form. Furthermore, phosphorylation at Ser-43-Pro has been observed to increase in the cerebral spinal fluid of sporadic Creutzfeldt-Jakob Disease patients. These findings provide new insights into the pathogenesis of prion disorders, suggesting Pin1 as a potential new player in the disease. In this paper, we review the mechanisms underlying Pin1 involvement in the aforementioned neurodegenerative pathologies focusing on the potential role of Pin1 in prion disorders
On some features of quadratic unconstrained binary optimization with random coefficients
No full textQuadratic Unconstrained Binary Optimization (QUBO or UBQP) is concerned with maximizing/minimizing the quadratic form H(J,eta)=W & sum;(i,j)J(i,j)eta(i)eta(j )with J a matrix of coefficients, eta is an element of {0,1}(N) and W a normalizing constant. In the statistical mechanics literature, QUBO is a lattice gas counterpart to the (generalized) Sherrington-Kirkpatrick spin glass model. Finding the optima of H is an NP-hard problem. Several problems in combinatorial optimization and data analysis can be mapped to QUBO in a straightforward manner. In the combinatorial optimization literature, random instances of QUBO are often used to test the effectiveness of heuristic algorithms. Here we consider QUBO with random independent coefficients and show that if the J(i,j)'s have zero mean and finite variance then, after proper normalization, the minimum and maximum per particle of H do not depend on the details of the distribution of the couplings and are concentrated around their expected values. Further, with the help of numerical simulations, we study the minimum and maximum of the objective function and provide some insight into the structure of the minimizer and the maximizer of H. We argue that also this structure is rather robust. Our findings hold also in the diluted case where each of the J(i,j)'s is allowed to be zero with probability going to 1 as N ->infinity in a suitable way
Observing the Cosmic Web with the Sunyaev-Zel’dovich effect: from ACT to MISTRAL
No full textThis thesis work gravitates around the broad field of the large scale structure and its observation using the Sunyaev-Zel’dovich effect, an anisotropic spectral distortion of the CMB that causes a decrement in brightness when observing in the direction of an hot electron population, like the ones contained in galaxy clusters or in cosmic filaments. The first part of this thesis focuses on observing bridges between interacting clusters, i.e. filaments compressed by merging clusters, using data from the Atacama Cosmology Telescope. We survey a preliminary version of the ACT-DR6 cluster catalog in order to search for significant filaments between clusters, and to measure their average properties by stacking. The second part of this work instead focuses on observing clusters and filaments at higher resolution compared to CMB experiments, using high resolution millimeter cameras. We introduce the MISTRAL receiver and follow the steps of its development, from the laboratory calibration to the first observations at the focus of the Sardinia Radio Telescope
Speed of Parallel Processing for Random Task Graphs
No full textThe random graph model of parallel computation introduced by Gelenbe et al. depends on three
parameters: n, the number of tasks (vertices); F, the common distribution of Ti,. . . , T,, the task
processing times, and p = p,, the probability for a given i < j that task i must be completed before
task j is started. The total processing time is R,,, the maximum sum of T,’s along directed paths of
the graph. We study the large n behavior of Rn when np,, grows sublinearly but superlogarithmically,
the regime where the longest directed path contains about enp,, tasks. For an exponential (mean one)
F, we prove that R,, is about 4np,. The “discrepancy” between 4 and e is a large deviation effect.
Related results are obtained when np,, grows exactly logarithmically and when F is not exponential,
but has a tail which decays (at least) exponentially fast
Quantum Methods for Interacting Particle Systems II, Glauber Dynamics for Ising Spin Systems
No full textUsing the formalism and the results described in [QMPS I] and in
[QMPS III], we discuss the approach to termodynamic equilibrium for discrete
spin systems in a framework that generalizes the one originally proposed by
R. Glauber. Ergodicity for the process is proved by providing a lower bound
extimate for their exponetial rate of convergence to equilibrium, in the high
temperature regime. We give application to some (not necessarily ferromagnetic ) Ising-spin models. These results also gives an upper bound for the
critical temperature of the d-dimensional Ising model, which in dimension two
coincides with the real critical value calculated by the static approach
ON THE LOCATION OF THE 1-PARTICLE BRANCH OF THE SPECTRUM OF THE DISORDERED STOCHASTIC ISING MODEL
No full textWe analyse the lower non trivial part of the spectrum of the generator of the Glauber dynamics for a d-dimensional nearest neighbour Ising model with a bounded random potential. We prove conjecture 1 in [1]: for sufficently large values of the temperature, the first band of the spectrum of the generator of the process coincides with a closed non random segment of the real line
Roles of specialized pro-resolving lipid mediators in autophagy and inflammation
No full textAutophagy is a catabolic pathway that accounts for degradation and recycling of cellular components to extend cell survival under stress conditions. In addition to this prominent role, recent evidence indicates that autophagy is crucially involved in the regulation of the inflammatory response, a tightly controlled process aimed at clearing the inflammatory stimulus and restoring tissue homeostasis. To be efficient and beneficial to the host, inflammation should be controlled by a resolution program, since uncontrolled inflammation is the underlying cause of many pathologies. Resolution of inflammation is an active process mediated by a variety of mediators, including the so-called specialized pro-resolving lipid mediators (SPMs), a family of endogenous lipid autacoids known to regulate leukocyte infiltration and activities, and counterbalance cytokine production. Recently, regulation of autophagic mechanisms by these mediators has emerged, uncovering unappreciated connections between inflammation resolution and autophagy. Here, we summarize mechanisms of autophagy and resolution, focusing on the contribution of autophagy in sustaining paradigmatic examples of chronic inflammatory disorders. Then, we discuss the evidence that SPMs can restore dysregulated autophagy, hypothesizing that resolution of inflammation could represent an innovative approach to modulate autophagy and its impact on the inflammatory response
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