376 research outputs found
Rotational intermittency and turbulence induced lift experienced by large particles in a turbulent flow
The motion of a large, neutrally buoyant, particle, freely advected by a
turbulent flow is determined experimentally. We demonstrate that both the
translational and angular accelerations exhibit very wide probability
distributions, a manifestation of intermittency. The orientation of the angular
velocity with respect to the trajectory, as well as the translational
acceleration conditioned on the spinning velocity provide evidence of a lift
force acting on the particle.Comment: 4 page, 4 figure
Tracking the dynamics of translation and absolute orientation of a sphere in a turbulent flow
We study the 6-dimensional dynamics -- position and orientation -- of a large
sphere advected by a turbulent flow. The movement of the sphere is recorded
with 2 high-speed cameras. Its orientation is tracked using a novel, efficient
algorithm; it is based on the identification of possible orientation
`candidates' at each time step, with the dynamics later obtained from
maximization of a likelihood function. Analysis of the resulting linear and
angular velocities and accelerations reveal a surprising intermittency for an
object whose size lies in the integral range, close to the integral scale of
the underlying turbulent flow
Characterizing flows with an instrumented particle measuring Lagrangian accelerations
We present in this article a novel Lagrangian measurement technique: an
instrumented particle which continuously transmits the force/acceleration
acting on it as it is advected in a flow. We develop signal processing methods
to extract information on the flow from the acceleration signal transmitted by
the particle. Notably, we are able to characterize the force acting on the
particle and to identify the presence of a permanent large-scale vortex
structure. Our technique provides a fast, robust and efficient tool to
characterize flows, and it is particularly suited to obtain Lagrangian
statistics along long trajectories or in cases where optical measurement
techniques are not or hardly applicable.Comment: submitted to New Journal of Physic
Eating and weight related cognitions in people with Schizophrenia : A case control study
BACKGROUND: Patients with antipsychotic-induced weight gain (WG) regularly report on unsuccessful dietary trials, which suggests strong biological weight gain drive that is extremely hard to overcome with thoughts, such that behaviour doesn't change despite some intent to change. The purpose of the present study was to assess cognitions specifically related to restrained eating in severely overweight patients with schizophrenia treated with antipsychotic drugs. METHODS: Forty outpatients with schizophrenia and 40 controls without psychiatric disability were included. Both groups were composed of one subgroup severely overweight (defined as a BMI > 28), and a comparison sample (BMI<28). The revised version of the Mizes Anorectic cognitive questionnaire (MAC-R) was used in this cross-sectional case-control study. RESULTS: Gender was significantly related to eating disorders cognition, women scoring higher than men. Patients with schizophrenia in general scored higher on the MAC-R total scale and on the MAC-R subscale 2, the latter score representing rigid weight regulation and fear of weight gain. When comparing the two groups of subjects with BMI < 28, it appeared that patients with schizophrenia also scored higher on MAC-R total scale, the subscales 2 and 3, the latter subscale 3, indicating altered self control and self-esteem. CONCLUSION: As is the case in weight gain of subjects without schizophrenia, the present results suggest that the cognitive distortions, as assessed by the MAC-R, may play an important role in weight gain also in patients with schizophrenia, and in weight gain associated with antipsychotic pharmacotherapy. Particular attention to these processes may help to improve the management of antipsychotic drugs induced weight gain
Herpes simplex virus hepatitis 4 years after liver transplantation
If not promptly recognized and treated, herpes simplex virus (HSV) hepatitis is associated with a high mortality. A patient transplanted for primary sclerosing cholangitis required, 4 years later, a colectomy for a steroid-resistant flare of ulcerative colitis. He subsequently developed fever, with genital and oral ulcerations. He was hospitalized for diabetic decompensation with massive elevation of serum aminotransferases. Examination revealed vesicles on the hands. Liver biopsy showed Cowdry type B inclusions. Therapy with acyclovir was immediately initiated and the patient recovered. This case illustrates the diagnostic importance of mucocutaneous lesions in the assessment of complications after liver transplantatio
Le radio-tracking des vertébrés : conseils et techniques d’utilisation
Recent advances in radio- tracking small vertebrates are reviewed. Practical suggestions are made on how to build cheap transmitters which can be used in tropical as well as temperate habitats
Co-occurrence, ecological profiles and geographical distribution based on unique molecular identifiers of the common freshwater diatoms Fragilaria and Ulnaria
Diatom taxonomy has evolved in recent years, with many new species described and new approaches such as molecular genetics showing the existence of cryptic diversity within currently accepted species. This cryptic diversity is not well understood even for common freshwater genera such as Fragilaria and Ulnaria. The purpose of our study was to define taxon-specific ecological profiles and geographical distributions for unique molecular identifiers (amplicon sequence variants, ASVs) linked to curated taxonomy for these genera. Our goal is to contribute to the development of ecological assessment methods, and to the understanding why we often observe so many diatom species co-occurring in a single sample. We filtered a large (770 samples) metabarcoding dataset with linked environmental data covering several countries in Europe for genetic variants (ASVs) assigned to currently accepted species of our target genera. We studied the geographical distribution of the ASVs, and tested for ASV-pair co-occurrence. We modelled ASV-specific preferences for pH, alkalinity, total nitrogen, total phosphorus and conductivity, and analysed their preference for lakes or streams as habitat. Our study confirmed that there seems to be no general geographical barrier for the distribution of freshwater benthic diatom ASVs in Europe, but that dispersal is not rapid enough to hide historical events. The Fragilaria and Ulnaria ASVs in our study showed considerable overlap in geographical distribution, habitat and ecological preferences. We found evidence that only large differences in preferences for the analysed water chemistry variables prevented the co-occurrence of ASVs at the same sites. Instead, Fragilaria and Ulnaria ASVs co-occurred frequently in samples. We found subtle differences in ecological preferences for some ASV pairs, which might in part explain the co-occurrence by the avoidance of direct competition. However, the great overlap in distribution and ecological preferences suggests that other factors not studied here were also responsible for the observed co-occurrences and high richness of ASVs found at many sites. To our knowledge, we are the first to use ASVs in combination with a curated taxonomy to understand co-occurrence, specific ecological profiles and large-scale geographical distribution for unique identifiers not biased by the quality of reference databases, clustering methods, or non-harmonized morphological identification. Thus, our results can now be used in subsequent projects to interpret ASV occurrences, e.g. for development of ecological assessment methods
Average Case Analysis of Unification Algorithms
International audienceUnification in first-order languages is a central operation in symbolic computation and logic programming. Many unification algorithms have been proposed in the past, however there is no consensus on which algorithm is the best to use in practice. While Paterson and Wegman's linear unification algorithm has the lowest time complexity in the worst case, it requires an important overhead to be implemented. This is true also, although less importantly, for Martelli and Montanari's algorithm [MM82], and Robinson's algorithm [Rob71] is finally retained in many applications despite its exponential worst-case time complexity. There are many explanations for that situation: one important argument is that in practice unification subproblems are not independent, and linear unification algorithms do not perform well on sequences of unify-deunify operations [MU86]. In this paper we present average case complexity theoretic arguments. We first show that the family of unifiable pairs of binary trees is exponentially negligible with respect to the family of arbitrary pairs of binary trees formed over l binary function symbols, c constants and v variables. We analyze the different reasons for failure and get asymptotical and numerical evaluations. We then extend the previous results of [DL89] to these families of trees, we show that a slight modification of Herbrand-Robinson's algorithm has a constant average cost on random pairs of trees. On the other hand, we show that various variants of Martelli and Montanari's algorithm all have a linear average cost on random pairs of trees. The point is that failures by clash are not sufficient to lead to a constant average cost, an efficient occur check (i.e. without a complete traversal of subterms) is necessary. In the last section we extend the results on the probability of the occur check in presence of an unbounded number of variables
Renormalization of Crumpled Manifolds
We consider a model of D-dimensional tethered manifold interacting by
excluded volume in R^d with a single point. By use of intrinsic distance
geometry, we first provide a rigorous definition of the analytic continuation
of its perturbative expansion for arbitrary D, 0 < D < 2. We then construct
explicitly a renormalization operation, ensuring renormalizability to all
orders. This is the first example of mathematical construction and
renormalization for an interacting extended object with continuous internal
dimension, encompassing field theory.Comment: 10 pages (1 figure, included), harvmac, SPhT/92-15
Renormalization Theory for Interacting Crumpled Manifolds
We consider a continuous model of D-dimensional elastic (polymerized)
manifold fluctuating in d-dimensional Euclidean space, interacting with a
single impurity via an attractive or repulsive delta-potential (but without
self-avoidance interactions). Except for D=1 (the polymer case), this model
cannot be mapped onto a local field theory. We show that the use of intrinsic
distance geometry allows for a rigorous construction of the high-temperature
perturbative expansion and for analytic continuation in the manifold dimension
D. We study the renormalization properties of the model for 0<D<2, and show
that for d<d* where d*=2D/(2-D) is the upper critical dimension, the
perturbative expansion is UV finite, while UV divergences occur as poles at
d=d*. The standard proof of perturbative renormalizability for local field
theories (the BPH theorem) does not apply to this model. We prove perturbative
renormalizability to all orders by constructing a subtraction operator based on
a generalization of the Zimmermann forests formalism, and which makes the
theory finite at d=d*. This subtraction operation corresponds to a
renormalization of the coupling constant of the model (strength of the
interaction with the impurity). The existence of a Wilson function, of an
epsilon-expansion around the critical dimension, of scaling laws for d<d* in
the repulsive case, and of non-trivial critical exponents of the delocalization
transition for d>d* in the attractive case is thus established. To our
knowledge, this provides the first proof of renormalizability for a model of
extended objects, and should be applicable to the study of self-avoidance
interactions for random manifolds.Comment: 126 pages (+ 24 figures not included available upon request),
harvmac, SPhT/92/12
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