Codescent theory I: Foundations

Consider a cofibrantly generated model category $S$, a small category $C$ and a subcategory $D$ of $C$. We endow the category $S^C$ of functors from $C$ to $S$ with a model structure, defining weak equivalences and fibrations objectwise but only on $D$. Our first concern is the effect of moving $C$, $D$ and $S$. The main notion introduced here is the ``$D$-codescent'' property for objects in $S^C$. Our long-term program aims at reformulating as codescent statements the Conjectures of Baum-Connes and Farrell-Jones, and at tackling them with new methods. Here, we set the grounds of a systematic theory of codescent, including pull-backs, push-forwards and various invariance properties.Comment: 48 pages (minor changes in the presentation and the references

A survey on algorithmic aspects of modular decomposition

The modular decomposition is a technique that applies but is not restricted to graphs. The notion of module naturally appears in the proofs of many graph theoretical theorems. Computing the modular decomposition tree is an important preprocessing step to solve a large number of combinatorial optimization problems. Since the first polynomial time algorithm in the early 70's, the algorithmic of the modular decomposition has known an important development. This paper survey the ideas and techniques that arose from this line of research

Model theoretic reformulation of the Baum-Connes and Farrell-Jones conjectures

The Isomorphism Conjectures are translated into the language of homotopical algebra, where they resemble Thomason's descent theorems.Comment: 4 page

Testing What’s at Stake: Defending Stakes Effects for Testimony

This paper investigates whether practical interests affect knowledge attributions in cases of testimony. It is argued that stakes impact testimonial knowledge attributions by increasing or decreasing the requirements for hearers to trust speakers and thereby gain the epistemic right to acquire knowledge via testimony. Standard, i.e. invariantist, reductionism and non-reductionism fail to provide a plausible account of testimony that is stakes sensitive, while non- invariantist versions of both traditional accounts can remedy this deficiency. Support for this conceptual analysis of stakes is found through a review of the experimental philosophy literature on stakes effects on knowledge attribution. Finally, a diagnosis is offered for what is needed to provide a more robust defense of the paper’s primary claims in terms of future experimental study

Regularization with Approximated L2L^2 Maximum Entropy Method

We tackle the inverse problem of reconstructing an unknown finite measure $\mu$ from a noisy observation of a generalized moment of $\mu$ defined as the integral of a continuous and bounded operator $\Phi$ with respect to $\mu$. When only a quadratic approximation $\Phi_m$ of the operator is known, we introduce the $L^2$ approximate maximum entropy solution as a minimizer of a convex functional subject to a sequence of convex constraints. Under several assumptions on the convex functional, the convergence of the approximate solution is established and rates of convergence are provided.Comment: 16 page

The preferred doctor scheme: A political reading of a French experiment of Gate-keeping

Study objective: Since January 2005 France is exploring a new scheme termed "preferred doctor" (médecin traitant) which can be considered as an innovative version of Gate Keeping in order to reduce the excess of postulated excess in health consumption, more especially access to specialist care. This paper describes the political process which lead to it's implementation, tries to relate some of the scheme specific features with it's results after one year implementation and tries to catch a glimpse for the next steps of the reform. Material and methods: In order to measure the scheme impact on the "patient treatment pathway" and on physician income, we used a sample of 7198 individual from the 2006 "French health, Health Care and Insurance Survey "(ESPS),"including health, socioeconomic and insurance status and through a set of questions relating to patient's understanding of the scheme and different data bases of the national sickness fund as well as different studies done by regulatory agencies. Results and discussion: First results after one year implementation show that most patients chose a preferred doctor, who in a vast majority happened to be their family doctor. A vast majority of patients also considered the scheme as mandatory. Impact on access to specialist care, as measured through self assessed unmet need for specialist care, appears not negligible, especially for the less well off and those not covered by a complementary insurance. In term of financial impact, the new constraints on access to ambulatory care seem to have been offset by rises in the fee schedules for the specialities which lost direct access We discuss why these short term weak outcomes are linked with a wicked system of the health system governance and to the political and professional context in which the scheme unfolded strongly and determined its structure and implementation pathway. On a more long range perspective, we analyse how the new scheme may nevertheless lead up to reinforced managed care reforms.Managed Care, Gate keeping, health care services utilization, unmet needs.

Lacunary formal power series and the Stern-Brocot sequence

Let $F(X) = \sum_{n \geq 0} (-1)^{\varepsilon_n} X^{-\lambda_n}$ be a real lacunary formal power series, where $\varepsilon_n = 0, 1$ and $\lambda_{n+1}/\lambda_n > 2$. It is known that the denominators $Q_n(X)$ of the convergents of its continued fraction expansion are polynomials with coefficients $0, \pm 1$, and that the number of nonzero terms in $Q_n(X)$ is the $n$th term of the Stern-Brocot sequence. We show that replacing the index $n$ by any 2-adic integer $\omega$ makes sense. We prove that $Q_{\omega}(X)$ is a polynomial if and only if $\omega \in {\mathbb Z}$. In all the other cases $Q_{\omega}(X)$ is an infinite formal power series, the algebraic properties of which we discuss in the special case $\lambda_n = 2^{n+1} - 1$.Comment: to appear in Acta Arithmetic

Does the Geometry of Word Embeddings Help Document Classification? A Case Study on Persistent Homology Based Representations

We investigate the pertinence of methods from algebraic topology for text data analysis. These methods enable the development of mathematically-principled isometric-invariant mappings from a set of vectors to a document embedding, which is stable with respect to the geometry of the document in the selected metric space. In this work, we evaluate the utility of these topology-based document representations in traditional NLP tasks, specifically document clustering and sentiment classification. We find that the embeddings do not benefit text analysis. In fact, performance is worse than simple techniques like $\textit{tf-idf}$, indicating that the geometry of the document does not provide enough variability for classification on the basis of topic or sentiment in the chosen datasets.Comment: 5 pages, 3 figures. Rep4NLP workshop at ACL 201

Why Firms Outsource Their Human Resources Activities: An Empirical Analysis

In this paper, we develop and estimate an explanatory model of Human Resources Outsourcing. Six HR activities are analyzed: Payroll, Benefits, Recruiting, Training, Labor Relations, and Human Resources Information Systems. The determinants of outsourcing are drawn from two fields: the field of organizational analysis and strategy formulation, and that from transaction-cost theory. Our results indicate that the drivers of HRO are rather specific to each type of activity. The transaction-cost determinants appear to play a particularly important role in the HRO decisions. In particular, the prior experience of the organization with outsourcing of other functions, the uncertainty of the transaction, and the presence of a union have a commanding influence. Ce mémoire développe et estime un modèle causal de l'impartition des ressources humaines. Six grandes activités ressources humaines sont analysées: la paie, les avantages sociaux, la dotation, la formation, les relations de travail et les systèmes d'information de ressources humaines. Les déterminants de l'impartition proviennent de deux littératures scientifiques : celle de la théorie des organisations et de la formulation de la stratégie d'une part, et celle de la théorie économique des coûts de transaction d'autre part. Nos résultats montrent que les déterminants de l'impartition varient d'activité à activité. Les déterminants suggérés par l'approche des coûts de transaction semblent jouer un rôle particulièrement important. L'expérience qu'ont les organisations avec l'impatition de d'autres fonctions, l'incertitude de la transaction et la présence d'un syndicat ont une influence prépondérante sur la décision d'impartir les activités ressources humaines.Outsourcing, human resources management, Impartition, gestion des ressources humaines