Débat sur les perspectives économiques à court terme du 11 avril 2011

Les prévisions occupent une place particulière dans le débat public en économie. Elles sont généralement considérées comme des prédictions, qualifiées fréquemment d’optimistes ou de pessimistes, comme si elles dépendaient de l’humeur des équipes qui les réalisent. Certes, en un sens, la prévision est un art tant elle dépend des signes précurseurs que nous livre le présent, de l’interprétation des évolutions en cours, de la capacité des économistes de sélectionner les informations pertinentes parmi celles, multiples, dont l’intérêt n’est qu’anecdotique. Mais elle est surtout une science puisqu’elle consiste à déduire des informations dont on dispose sur le présent une vision de l’avenir. Elle ne peut être formulée en dehors d’un cadre général d’interprétation, c’est-à-dire d’une théorie qui met en relation les informations que l’on privilégie et les variables que l’on cherche à prévoir. Parmi ces informations, certaines, cruciales, ne sont pas vraiment disponibles car, pour l'essentiel, elles dépendent de décisions à venir et qu'il n'existe pas vraiment de théorie permettant de déduire des données existantes ce que seront ces décisions. Il faut donc formuler des hypothèses alternatives et retenir celles qui paraissent les plus vraisemblables. Dès lors, les erreurs de prévision peuvent avoir au moins trois origines : une insuffisance d'information sur le présent, une mauvaise spécification théorique, la non réalisation de certaines hypothèses. De surcroît, il existe une incertitude irréductible au sens où certains événements sont imprévisibles, alors même que leur conséquence sur l'activité économique est déterminante. Voilà pourquoi les chiffres associés à une prévision sont éminemment fragiles, qu'ils doivent être considérés comme conditionnels aux hypothèses que l'on formule, aux données dont on dispose et au cadre théorique dans lequel on raisonne. Il est donc nécessaire que les prévisions réalisées par l'OFCE soient publiées en même temps qu'un débat autour de ces prévisions. Cela offre le double avantage de rendre explicite le doute inhérent à tout exercice de prévision et de participer au pluralisme nécessaire à l'indépendance et au sérieux des études économiques. Les prévisions de l'OFCE, pour rigoureuses qu'elles soient, ne sont pas un exercice mécanique au terme duquel la vérité serait révélée mais une " histoire " raisonnée, éclairée par l'analyse économique, d'un futur incertain. Il faut donc à la fois souligner l'importance des raisonnements économiques qui la guident et en comprendre d'emblée les limites, pour ne point s'en servir comme d'un argument d'autorité à l'instar de ce qui est trop fréquemment le cas

Cardiac troponin and skeletal muscle oxygenation in severe post-partum haemorrhage

International audienceIntroductionCardiac troponin has been shown to be elevated in one-half of the parturients admitted for post-partum haemorrhage. The purpose of the study was to assess whether increased cardiac troponin was associated with a simultaneous alteration in haemoglobin tissue oxygen saturation in peripheral muscles in post-partum haemorrhage.MethodsTissue haemoglobin oxygen saturation of thenar eminence muscle (StO2) was measured via near-infrared spectroscopy technology. Two sets of StO2 parameters (both isolated baseline and during forearm ischaemia-reperfusion tests) were collected at two time points: upon intensive care unit admission and prior to intensive care unit discharge. Comparisons were performed using Wilcoxon paired tests, and univariate associations were assessed using logistic regression model and Wald tests.ResultsThe 42 studied parturients, admitted for post-partum haemorrhage, had clinical and biological signs of severe blood loss. Initial cardiac troponin I was increased in 24/42 parturients (0.43 ± 0.60 μrg/l). All measured parameters of muscular haemoglobin oxygen saturation, including Srecovery, were also altered at admission and improved together with improved haemodynamics, when bleeding was controlled. Multivariate analysis showed that muscular Srecovery ConclusionsOur study confirmed the high incidence of increased cardiac troponin, and demonstrated the simultaneous impairment in the reserve of oxygen delivery to peripheral muscles in parturients admitted for severe post-partum haemorrhage

The orientations of molecular clouds in the outer Galaxy: Evidence for the scale of the turbulence driver ?

Supernova explosions inject a considerable amount of energy into the interstellar medium (ISM) in regions with high to moderate star formation rates. In order to assess whether the driving of turbulence by supernovae is also important in the outer Galactic disk, where the star formation rates are lower, we study the spatial distribution of molecular cloud (MC) inclinations with respect to the Galactic plane. The latter contains important information on the nature of the mechanism of energy injection into the ISM. We analyze the spatial correlations between the position angles (PAs) of a selected sample of MCs (the largest clouds in the catalogue of the outer Galaxy published by Heyer et al. 2001). Our results show that when the PAs of the clouds are all mapped to values into the [0,90]degrees interval, there is a significant degree of spatial correlation between the $PA$s on spatial scales in the range of 100-800 pc. These scales are of the order of the sizes of individual SN shells in low density environments such as those prevailing in the outer Galaxy and where the metallicity of the ambient gas is of the order of the solar value or smaller. These findings suggest that individual SN explosions, occurring in the outer regions of the Galaxy and in likewise spiral galaxies, albeit at lower rates, continue to play an important role in shaping the structure and dynamics of the ISM in those regions. The SN explosions we postulate here are likely associated with the existence of young stellar clusters in the far outer regions of the Galaxy and the UV emission and low levels of star formation observed with the GALEX satellite in the outer regions of local galaxies.Comment: Accepted to MNRAS main journal. Additional discussion and and one figure with error estimates is added. 7 pages, 7 figures. Main conclusions unchange

AzTEC 1.1 mm Observations of the MBM12 Molecular Cloud

We present 1.1 mm observations of the dust continuum emission from the MBM12 high-latitude molecular cloud observed with the Astronomical Thermal Emission Camera (AzTEC) mounted on the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. We surveyed a 6.34 deg$^2$ centered on MBM12, making this the largest area that has ever been surveyed in this region with submillimeter and millimeter telescopes. Eight secure individual sources were detected with a signal-to-noise ratio of over 4.4. These eight AzTEC sources can be considered to be real astronomical objects compared to the other candidates based on calculations of the false detection rate. The distribution of the detected 1.1 mm sources or compact 1.1 mm peaks is spatially anti-correlated with that of the 100 micronm emission and the $^{12}$CO emission. We detected the 1.1 mm dust continuum emitting sources associated with two classical T Tauri stars, LkHalpha262 and LkHalpha264. Observations of spectral energy distributions (SEDs) indicate that LkHalpha262 is likely to be Class II (pre-main-sequence star), but there are also indications that it could be a late Class I (protostar). A flared disk and a bipolar cavity in the models of Class I sources lead to more complicated SEDs. From the present AzTEC observations of the MBM12 region, it appears that other sources detected with AzTEC are likely to be extragalactic and located behind MBM12. Some of these have radio counterparts and their star formation rates are derived from a fit of the SEDs to the photometric evolution of galaxies in which the effects of a dusty interstellar medium have been included.Comment: 8 pages, 6 figures, The Astrophysical Journal, in pres

Is The Amphibian Tree of Life really fatally flawed?

Wiens (2007 , Q. Rev. Biol. 82, 55–56) recently published a severe critique of Frost et al.'s (2006, Bull. Am. Mus. Nat. Hist. 297, 1–370) monographic study of amphibian systematics, concluding that it is “a disaster” and recommending that readers “simply ignore this study”. Beyond the hyperbole, Wiens raised four general objections that he regarded as “fatal flaws”: (1) the sampling design was insufficient for the generic changes made and taxonomic changes were made without including all type species; (2) the nuclear gene most commonly used in amphibian phylogenetics, RAG-1, was not included, nor were the morphological characters that had justified the older taxonomy; (3) the analytical method employed is questionable because equally weighted parsimony “assumes that all characters are evolving at equal rates”; and (4) the results were at times “clearly erroneous”, as evidenced by the inferred non-monophyly of marsupial frogs. In this paper we respond to these criticisms. In brief: (1) the study of Frost et al. did not exist in a vacuum and we discussed our evidence and evidence previously obtained by others that documented the non-monophyletic taxa that we corrected. Beyond that, we agree that all type species should ideally be included, but inclusion of all potentially relevant type species is not feasible in a study of the magnitude of Frost et al. and we contend that this should not prevent progress in the formulation of phylogenetic hypotheses or their application outside of systematics. (2) Rhodopsin, a gene included by Frost et al. is the nuclear gene that is most commonly used in amphibian systematics, not RAG-1. Regardless, ignoring a study because of the absence of a single locus strikes us as unsound practice. With respect to previously hypothesized morphological synapomorphies, Frost et al. provided a lengthy review of the published evidence for all groups, and this was used to inform taxonomic decisions. We noted that confirming and reconciling all morphological transformation series published among previous studies needed to be done, and we included evidence from the only published data set at that time to explicitly code morphological characters (including a number of traditionally applied synapomorphies from adult morphology) across the bulk of the diversity of amphibians (Haas, 2003, Cladistics 19, 23–90). Moreover, the phylogenetic results of the Frost et al. study were largely consistent with previous morphological and molecular studies and where they differed, this was discussed with reference to the weight of evidence. (3) The claim that equally weighted parsimony assumes that all characters are evolving at equal rates has been shown to be false in both analytical and simulation studies. (4) The claimed “strong support” for marsupial frog monophyly is questionable. Several studies have also found marsupial frogs to be non-monophyletic. Wiens et al. (2005, Syst. Biol. 54, 719–748) recovered marsupial frogs as monophyletic, but that result was strongly supported only by Bayesian clade confidence values (which are known to overestimate support) and bootstrap support in his parsimony analysis was < 50%. Further, in a more recent parsimony analysis of an expanded data set that included RAG-1 and the three traditional morphological synapomorphies of marsupial frogs, Wiens et al. (2006, Am. Nat. 168, 579–596) also found them to be non-monophyletic. Although we attempted to apply the rule of monophyly to the naming of taxonomic groups, our phylogenetic results are largely consistent with conventional views even if not with the taxonomy current at the time of our writing. Most of our taxonomic changes addressed examples of non-monophyly that had previously been known or suspected (e.g., the non-monophyly of traditional Hyperoliidae, Microhylidae, Hemiphractinae, Leptodactylidae, Phrynobatrachus , Ranidae, Rana , Bufo ; and the placement of Brachycephalus within “ Eleutherodactylus ”, and Lineatriton within “ Pseudoeurycea ”), and it is troubling that Wiens and others, as evidenced by recent publications, continue to perpetuate recognition of non-monophyletic taxonomic groups that so profoundly misrepresent what is known about amphibian phylogeny. © The Willi Hennig Society 2007.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74688/1/j.1096-0031.2007.00181.x.pd