Improving non-linear fits

In this notes we describe an algorithm for non-linear fitting which incorporates some of the features of linear least squares into a general minimum $\chi^2$ fit and provide a pure Python implementation of the algorithm. It consists of the variable projection method (varpro), combined with a Newton optimizer and stabilized using the steepest descent with an adaptative step. The algorithm includes a term to account for Bayesian priors. We performed tests of the algorithm using simulated data. This method is suitable, for example, for fitting with sums of exponentials as often needed in Lattice Quantum Chromodynamics

Systemic lupus erythematosus and hearing disorders: literature review and meta-analysis of clinical and temporal bone findings

Objective: This literature review and meta-analysis was performed to evaluate the correlations among hearing and vestibular clinical symptoms, temporal bone findings, and pathological mechanisms in patients with systemic lupus erythematosus (SLE). Study design: Relevant papers in the literature were retrospectively reviewed. Clinical hearing aspects in patients with SLE and relevant temporal bone studies in the same field were analyzed. Methods: PubMed and Google Scholar searches were performed using the following keywords: “auto-immune disease,” “systemic lupus erythematosus (SLE),” “hearing loss,” “temporal bone study,” “vertigo,” “dizziness,” “tinnitus,” “ear symptoms,” “treatment,” “diagnosis,” “symptoms,” “etiopathogenesis,” “Wegener granulomatosis,” “Sjogren,” “polyarteritis nodosa,” “Cogan syndrome,” and “granulomatosis.” Also included were reviews in which the following terms were present: “SLE,” “temporal bone,” and “hearing symptoms.” Review and conclusion: This literature review and meta-analysis focused on the pathological mechanisms through which SLE can damage inner ear structures and determinate hearing and vestibular symptoms. The main mechanisms involved in inner ear damage include the autoimmune response, deposition of immune complexes in the vessels and, to a lesser extent, cytotoxic damage

Trade, migration, and environment: a general equilibrium analysis, Chapter 2.3

Two major trends in the world economy are international migration and environmental degradation. The object of the paper is to analyze the connection between these two trends, which have generally been analyzed in isolation. Here we represent a world economy in which the exploitation of natural resources as well as the migration of labor have a global character. We discuss the welfare impact of migration and exploitation of natural resources and policies to address these issues. The main results of the paper are as follows. Migration is prompted by wage differentials as technology is different across countries. We show that migration from the South induces a decrease in the exploitation of the resource in the South. This increases the welfare of the South but can decrease that of the North. Migration can lead to higher prices ofresources in the North and in the South, setting up a process of induced technical change in the North and better terms of trade for the South, altogether a positive outcome. As is intuitively obvious, migration reduces the wage differential between North and South in a model where, contrary to Heckscher-Ohlin assumptions, technologies differ between countries. Finally, we show that it is possible that a tax on the use of the resource in the South induces an increase in its extraction rather than a decrease. Trade policies could have a positive impact on resource extraction, could reduce the wage gap and therefore decrease the economic incentive to the mobility of labour.general equilibrium; migration; international trade; environment; labor migration; wage differentials; resource extraction; welfare; policy

Simulation model of the logistic distribution in a medical oxygen supply chain

Research activities on operations management in the last years are always more dedicated to supply chain and logistics optimization models. The study belongs to this branch and describes the problems related to a re-configuration of the distribution net in a company that produces medical oxygen cylinders for Italian market. The enterprise is particularly sensible to the optimization of supplying processes due to the characteristics of its product, as any delay in the delivery could create dangerous health situation for patients. The work has the objective to realize a software for supply chain management that could be a decision support system, analyzing strategic impacts that changes in distribution system create. In details, the model shows the differences in service level in case of closing one or more factories and the relative necessary changes in logistics net. The paper is articulated in the following parts: • analysis of company and construction of simulation model; • study of classic operation research techniques to solve dynamic vehicle routing problems; • description of possible scenes derived by strategic decision in closing factories; analysis of experiments and global conclusions and developments