A test of long memory hypothesis based on self-similarity

This paper develops a new test of true versus spurious long memory, based on log-periodogram estimation of the long memory parameter using skip-sampled data. A correction factor is derived to overcome the bias in this estimator due to aliasing. The procedure is designed to be used in the context of a conventional test of significance of the long memory parameter, and composite test procedure described that has the properties of known asymptotic size and consistency. The test is implemented using the bootstrap, with the distribution under the null hypothesis being approximated using a dependent-sample bootstrap technique to approximate short-run dependence following fractional differencing. The properties of the test are investigated in a set of Monte Carlo experiments. The procedure is illustrated by applications to exchange rate volatility and dividend growth series.

Revisiting Shiller’s excess volatility hypothesis

One of the cornerstone of financial anomalies is that there exists money making opportunities. Shiller’s excess volatility theory is re-investigated from the perspective of a trading strategy where the present value is computed using a series of simple econometric models to forecast the present value. The results show that the excess volatility may not be exploited given the data available until time t. However, when learning is introduced empirically, the simple trading strategy may offer profits, but which are likely to disappear once transaction costs are considered.

Revisiting the diacylglycerol-induced insulin resistance hypothesis.

Obesity is associated with skeletal muscle insulin resistance, which is a crucial step in the development of type 2 diabetes. Among the mechanisms by which obesity may lead to insulin resistance, lipotoxicity is one of the hypotheses being explored; others include inflammation or the oxidative stress hypotheses. This review focuses on the role of diacylglycerols (DAG), a family of lipid metabolites implicated in the pathogenesis of lipotoxicity and insulin resistance. While recent studies report contradictory results in humans with regard to the importance of DAG-induced insulin resistance in skeletal muscle, other current literature highlight a potential role for DAG as signalling molecules. This review will discuss possible hypotheses explaining these contradictory results and the need to explore further the role of DAG in human metabolism.

L'ús dels clítics pronominals del català i la seva adquisició per parlants de romanès i de tagal

El nostre estudi ha analitzat els mecanismes de transferència de la L1 en dos grups de parlants, un que té el romanès i l’altre el tagal com a llengües mare, en el procés d’aprenentatge del català com a L2. En concret ens hem centrat en l’estudi de l’ús dels clítics pronominals, una de les parts de la gramàtica catalana més apassionant per les seves idiosincràsies i la seva diversitat formal. L’ús d’aquest tipus de pronoms és un aspecte que resulta complicat d’adquirir per parlants de llengües en què no existeixen o on l’ús que en fan és diferent. En el nostre estudi, ens hem basat inicialment en la descripció de les característiques fonamentals dels clítics pronominals del català, del romanès i del tagal, a partir de bibliografia especialitzada i més general, i, en el cas del català, fent servir també la pròpia competència. Després d’aquest apartat més descriptiu, hem utilitzat un corpus d’entrevistes fetes en català a dos grups de parlants, el primer amb aprenents de català que tenen el romanès com a L1 i el segon amb aprenents de català que tenen el tagal com a L1, per analitzar quantitativament i qualitativament l’ús dels clítics pronominals. Un altre grup d’entrevistes, aquesta vegada a persones autòctones (català L1), ens ha servit com a grup de control. El nostre estudi dóna suport a la hipòtesi que atorga una importància especial a la transferència de la L1 en l’adquisició d'una segona llengua en general, i en la dels clítics pronominals d’una llengua romànica, en particular. Els resultats mostren que hi ha diferències entre els dos grups d'aprenents que són estadísticament significatives (ús del programa SPSS) i poden ser atribuïdes a les característiques de la L1.

Uncovering a role for micro-RNAs in sleep homeostasis and energy metabolism

Micro-RNAs (miRNAs) are key, post-transcriptional regulators of gene expression and have been implicated in almost every cellular process investigated thus far. However, their role in sleep, in particular the homeostatic aspect of sleep control, has received little attention. We here assessed the effects of sleep deprivation on the brain miRNA transcriptome in the mouse. Sleep deprivation affected miRNA expression in a brain-region specific manner. The forebrain expression of the miRNA miR-709 was affected the most and in situ analyses confirmed its robust increase throughout the brain, especially in the cerebral cortex and the hippocampus. The hippocampus was a major target of the sleep deprivation affecting 37 miRNAs compared to 52 in the whole forebrain. Moreover, independent from the sleep deprivation condition, miRNA expression was highly region-specific with 45% of all expressed miRNAs showing higher expression in hippocampus and 55% in cortex. Next we demonstrated that down-regulation of miRNAs in Com/c2o-expressing neurons of adult mice, through a conditional and inducible Dicer knockout mice model (cKO), results in an altered homeostatic response after sleep deprivation eight weeks following the tamoxifen-induced recombination. Dicer cKO mice showed a larger increase in the electro-encephalographic (EEG) marker of sleep pressure, EEG delta power, and a reduced Rapid Eye Movement sleep rebound, compared to controls, highlighting a functional role of miRNAs in sleep homeostasis. Beside a sleep phenotype, Dicer cKO mice developed an unexpected, severe obesity phenotype associated with hyperphagia and altered metabolism. Even more surprisingly, after reaching maximum body weight 5 weeks after tamoxifen injection, obese cKO mice spontaneously started losing weight as rapidly as it was gained. Brain transcriptome analyses in obese mice identified several obesity-related pathways (e.g. leptin, somatostatin, and nemo-like kinase signaling), as well as genes involved in feeding and appetite (e.g. Pmch, Neurotensin). A gene cluster with anti-correlated expression in the cerebral cortex of post-obese compared to obese mice was enriched for synaptic plasticity pathways. While other studies have identified a role for miRNAs in obesity, we here present a unique model that allows for the study of processes involved in reversing obesity. Moreover, our study identified the cortex as a brain area important for body weight homeostasis. Together, these observations strongly suggest a role for miRNAs in the maintenance of homeostatic processes in the mouse, and support the hypothesis of a tight relationship between sleep and metabolism at a molecular - Les micro-ARNS (miARNs) sont des régulateurs post-transcriptionnels de l'expression des gènes, impliqués dans la quasi-totalité des processus cellulaires. Cependant, leur rôle dans la régulation du sommeil, et en particulier dans le maintien de l'homéostasie du sommeil, n'a reçu que très peu d'attention jusqu'à présent. Dans cette étude, nous avons étudié les conséquences d'une privation de sommeil sur l'expression cérébrale des miARNs chez la souris, et observé des changements dans l'expression de nombreux miARNs. Dans le cerveau antérieur, miR-709 est le miARN le plus affecté par la perte de sommeil, en particulier dans le cortex cérébral et l'hippocampe. L'hippocampe est la région la plus touchée avec 37 miARNs changés comparés à 52 dans le cerveau entier. Par ailleurs, indépendamment de la privation de sommeil, certains miARNs sont spécifiquement enrichis dans certaines aires cérébrales, 45% des miARNs étant surexprimés dans l'hippocampe contre 55% dans le cortex. Dans une seconde étude, nous avons observé que la délétion de DICER, enzyme essentielle à la biosynthèse des miARNs, et la perte subséquente des miARNs dans les neurones exprimant la protéine CAMK2a altère la réponse homéostatique à une privation de sommeil, 8 semaines après l'induction de la recombinaison génétique par le tamoxifen. Les souris sans Dicer (cKO) ont une plus large augmentation de l'EEG delta power, le principal marqueur électro-encéphalographique du besoin de sommeil, comparée aux contrôles, ainsi qu'un rebond en sommeil paradoxal plus petit. De façon surprenante, les souris Dicer cKO développent une obésité rapide, sévère et transitoire, associée à de l'hyperphagie et une altération de leur métabolisme énergétique. Après avoir atteint un pic maximal d'obésité, les souris cKO entrent spontanément dans une période de perte de poids rapide. L'analyse du transcriptome cérébral des souris obèses nous a permis d'identifier des voies associées à l'obésité (leptine, somatostatine et nemo-like kinase), et à la prise alimentaire (Pmch, Neurotensin), tandis que celui des souris post-obèses a révélé un groupe de gènes liés à la plasticité synaptique. Au-delà des nombreux modèles d'obésité existant chez la souris, notre étude présente un modèle unique permettant d'étudier les mécanismes sous-jacent la perte de poids. De plus, nous avons mis en évidence un rôle important du cortex cérébral dans le maintien de la balance énergétique. En conclusion, toutes ces observations soutiennent l'idée que les miARNs sont des régulateurs cruciaux dans le maintien des processus homéostatiques et confortent l'hypothèse d'une étroite relation moléculaire entre le sommeil et le métabolisme.

Benign Intrapulmonary Schwannoma: Aspect on F-18 Fluorodeoxyglucose PET/CT.

A 75-year-old man, with no significant symptoms, was referred after the incidental finding of a left hilar pulmonary mass of 30 × 30 × 50 mm on a chest CT. F-18 fluorodeoxyglucose (FDG) PET/CT demonstrated a heterogeneous, moderate radiotracer uptake in the mass (SUV 3.5 g/mL). Bronchoscopy revealed a discrete extrinsic compression of the superior bronchus without endobronchial lesion. Endobronchial fine-needle biopsies could not deliver a final diagnosis. The patient underwent upper lobectomy by thoracotomy. Histopathology revealed a benign intrapulmonary schwannoma. Although rare, intermediate FDG uptake in the settings of a pulmonary mass should include schwannoma in the differential diagnosis.

Immunocompetence and nestling survival in the house martin: the tasty chick hypothesis

In altricial birds post-fledging survival is usually positively related to nestling body mass. A large number of studies have shown that the latest hatched chick is the more likely to die, even if food is abundant. Here we suggest that ectoparasites may be a key factor in the evolution and the maintenance of the establishment of weight hierarchies within broods. We prepose the hypothesis that weight hierarchies within broods may be adaptive if the chick in poor condition is the one with the least efficient immune system within a nest. In this case parasites would preferentially feed on such a "tasty chick", because it would allow high reproductive rates for the parasites, without negatively affecting the survival of the other nestlings. This could prevent entire nest failure of the brood or allow the other chicks to grow more efficiently. This hypothesis was investigated in a colony of house martins Delichon urbica. We predicted that immunocompetence was positively correlated with body condition, and that nestlings dying before hedging should have lower immune responses when challenged with an antigen. T-cell immune response to an experimentally injected antigen was strongly positively related to body condition. Non-surviving chicks had low body condition and a weak immune response. The implications of these results are discussed in the context of the adaptive significance of hatching asynchrony.

Pre-hatching maternal effects and the tasty chick hypothesis

Question: Are maternal effects (i.e. maternal transfer of immune components to their offspring via the placenta or the egg) specifically directed to the offspring on which ectoparasites predictably aggregate? Organisms: The barn owl (Tyto alba) because late-hatched offspring are the main target of the ectoparasitic fly Carnus hemapterus. Hypothesis: Pre-hatching maternal effects enhance parasite resistance of late- compared with early-hatched nestlings. Search method: To disentangle the effect of natal from rearing ranks on parasite intensity, we exchanged hatchlings between nests to allocate early- and late-hatched hatchlings randomly in the within-brood age hierarchy. Result: After controlling for rearing ranks, cross-fostered late-hatched nestlings were less parasitized but lighter than cross-fostered early-hatched nestlings. Conclusion: Pre-hatching maternal effects increase parasite resistance of late-hatched offspring at a growth cost.

Omics meets hypothesis-driven research. Partnership for innovative discoveries in vascular biology and angiogenesis.

The emergence of omics technologies allowing the global analysis of a given biological or molecular system, rather than the study of its individual components, has revolutionized biomedical research, including cardiovascular medicine research in the past decade. These developments raised the prospect that classical, hypothesis-driven, single gene-based approaches may soon become obsolete. The experience accumulated so far, however, indicates that omic technologies only represent tools similar to those classically used by scientists in the past and nowadays, to make hypothesis and build models, with the main difference that they generate large amounts of unbiased information. Thus, omics and classical hypothesis-driven research are rather complementary approaches with the potential to effectively synergize to boost research in many fields, including cardiovascular medicine. In this article we discuss some general aspects of omics approaches, and review contributions in three areas of vascular biology, thrombosis and haemostasis, atherosclerosis and angiogenesis, in which omics approaches have already been applied (vasculomics).

Estat de la qüestió de l'estudi de l'aspecte lèxic : una proposta cognitiva de classficació d'esdeveniments

Peer-reviewed

Mètodes empírics en lingüística cognitiva

Peer-reviewed