Planktivores and plankton dynamics : effects of fish biomass and planktivore type

Les auteurs ont quantifié les incidences de la biomasse et du type de planctophage dans le cadre d'une étude expérimentale en mésocosmes. Cette étude était conçue en fonction d'un plan factoriel d'expérience combinant cinq niveaux de biomasse de poisson (de O, à 75 g/m3) avec deux types de planctophage, soit l'alose à gésier (#Dorosoma cepedianum), un filtreur, et le crapet arlequin (#Lepomis macrochirus), un chasseur visuel. Une augmentation de la biomasse de poisson était accompagnée d'une baisse du nombre de cladocères, de cyclopoïdes et de chironomides et de la teneur en phosphore particulaire ...; inversement l'abondance de rotifères, de flagellés unicellulaires, d'algues vertes coloniales et unicellulaires, de diatomées pennées, la productivité primaire, la turbidité et les teneurs en chlorophylle a, en phosphore total ... ont augmenté ... Bien que la chaîne des cascades trophiques de l'alose à gésier et celle du crapet soleil soient différentes, la biomasse de poisson jouait un rôle plus important que le type de planctophage comme régulateur des communautés planctoniques et de la qualité de l'eau. (D'après résumé d'auteur

A Weighted Estimate for the Square Function on the Unit Ball in \C^n

We show that the Lusin area integral or the square function on the unit ball of \C^n, regarded as an operator in weighted space $L^2(w)$ has a linear bound in terms of the invariant $A_2$ characteristic of the weight. We show a dimension-free estimate for the ``area-integral'' associated to the weighted $L^2(w)$ norm of the square function. We prove the equivalence of the classical and the invariant $A_2$ classes.Comment: 11 pages, to appear in Arkiv for Matemati

A New Look at Mode Conversion in a Stratified Isothermal Atmosphere

Recent numerical investigations of wave propagation near coronal magnetic null points (McLaughlin and Hood: Astron. Astrophys. 459, 641,2006) have indicated how a fast MHD wave partially converts into a slow MHD wave as the disturbance passes from a low-beta plasma to a high-beta plasma. This is a complex process and a clear understanding of the conversion mechanism requires the detailed investigation of a simpler model. An investigation of mode conversion in a stratified, isothermal atmosphere, with a uniform, vertical magnetic field is carried out, both numerically and analytically. In contrast to previous investigations of upward-propagating waves (Zhugzhda and Dzhalilov: Astron. Astrophys. 112, 16, 1982a; Cally: Astrophys. J. 548, 473, 2001), this paper studies the downward propagation of waves from a low-beta to high-beta environment. A simple expression for the amplitude of the transmitted wave is compared with the numerical solution.Comment: 14 pages, 6 figure

Thirteen years follow-up after radical transsternal thymectomy for myasthenia gravis. Do short-term results predict long-term outcome?

Objective: Long-term evaluation of efficacy and quality of life after radical surgical approach for myasthenia gravis (MG). Comparison between short-term follow-up and long-term outcome. Methods: All patients (n=26, 16 men and 10 women, mean age: 40.7 years) underwent total transsternal thymectomy for MG between 1986 and 1989. Prospective analysis of the patients for short-term follow-up (mean 22.4 months) was published in 1991. The same group of patients was reevaluated in 2001 (range of follow-up 11.4-15.2 years) and assessed according to the classification of Osserman and Oosterhuis. Results: Mean follow-up was 13.0 years (range 11.4-15.2 years). Two patients were lost from follow-up and one died 4 years after thymectomy for reasons unrelated to MG (n=23). No early or late postoperative mortality was observed. One sternal osteomyelitis occurred. Late postoperative morbidity included sternal instabilities (n=2), mild residual thoracic pain (n=6), and hypertrophic scars (n=7). Five patients were rehospitalized for aggravating MG and needed plasmapheresis (n=3) and intubation (n=1). Thirteen patients (56.5%) showed objective clinical improvement, including six patients (26.1%) with complete remission. Eleven patients (47.8%) do not take any medication at all. Because some late relapse may occur several years after operation, the rate of improvement decreased slightly, whereas the difference between short and long-term follow-up was not statistically significant (P=0.405). Twenty patients (87%) returned to work, including part-time occupation (n=4). Fourteen patients (61%) are performing sports regularly. Conclusions: Our data confirm that radical, transsternal thymectomy is an effective and safe therapeutic modality for MG. Short-term results seem to deteriorate over time, therefore long-term studies for minimally invasive approaches have to prove equal results before replacing the standard procedur

Reproducing Kernels of Generalized Sobolev Spaces via a Green Function Approach with Distributional Operators

In this paper we introduce a generalized Sobolev space by defining a semi-inner product formulated in terms of a vector distributional operator $\mathbf{P}$ consisting of finitely or countably many distributional operators $P_n$, which are defined on the dual space of the Schwartz space. The types of operators we consider include not only differential operators, but also more general distributional operators such as pseudo-differential operators. We deduce that a certain appropriate full-space Green function $G$ with respect to $L:=\mathbf{P}^{\ast T}\mathbf{P}$ now becomes a conditionally positive definite function. In order to support this claim we ensure that the distributional adjoint operator $\mathbf{P}^{\ast}$ of $\mathbf{P}$ is well-defined in the distributional sense. Under sufficient conditions, the native space (reproducing-kernel Hilbert space) associated with the Green function $G$ can be isometrically embedded into or even be isometrically equivalent to a generalized Sobolev space. As an application, we take linear combinations of translates of the Green function with possibly added polynomial terms and construct a multivariate minimum-norm interpolant $s_{f,X}$ to data values sampled from an unknown generalized Sobolev function $f$ at data sites located in some set $X \subset \mathbb{R}^d$. We provide several examples, such as Mat\'ern kernels or Gaussian kernels, that illustrate how many reproducing-kernel Hilbert spaces of well-known reproducing kernels are isometrically equivalent to a generalized Sobolev space. These examples further illustrate how we can rescale the Sobolev spaces by the vector distributional operator $\mathbf{P}$. Introducing the notion of scale as part of the definition of a generalized Sobolev space may help us to choose the "best" kernel function for kernel-based approximation methods.Comment: Update version of the publish at Num. Math. closed to Qi Ye's Ph.D. thesis (\url{http://mypages.iit.edu/~qye3/PhdThesis-2012-AMS-QiYe-IIT.pdf}

Can sand dunes be used to study historic storm events?

Knowing the long-term frequency of high magnitude storm events that cause coastal inundation is critical for present coastal management, especially in the context of rising sea levels and potentially increasing frequency and severity of storm events. Coastal sand dunes may provide a sedimentary archive of past storm events from which long-term frequencies of large storms can be reconstructed. This study uses novel portable optically stimulated luminescence (POSL) profiles from coastal dunes to reconstruct the sedimentary archive of storm and surge activity for Norfolk, UK. Application of POSL profiling with supporting luminescence ages and particle size analysis to coastal dunes provides not only information of dunefield evolution but also on past coastal storms. In this study, seven storm events, two major, were identified from the dune archive spanning the last 140 years. These appear to correspond to historical reports of major storm surges. Dunes appear to be only recording (at least at the sampling resolution used here) the highest storm levels that were associated with significant flooding. As such the approach seems to hold promise to obtain a better understanding of the frequency of large storms by extending the dune archive records further back to times when documentation of storm surges was sparse

Statistics of Wave Functions in Coupled Chaotic Systems

Using the supersymmetry technique, we calculate the joint distribution of local densities of electron wavefunctions in two coupled disordered or chaotic quantum billiards. We find novel spatial correlations that are absent in a single chaotic system. Our exact result can be interpreted for small coupling in terms of the hybridization of eigenstates of the isolated billiards. We show that the presented picture is universal, independent of microscopic details of the coupling.Comment: 4 pages, 2 figures; acknowledgements and references adde

Fourier Analysis of Gapped Time Series: Improved Estimates of Solar and Stellar Oscillation Parameters

Quantitative helio- and asteroseismology require very precise measurements of the frequencies, amplitudes, and lifetimes of the global modes of stellar oscillation. It is common knowledge that the precision of these measurements depends on the total length (T), quality, and completeness of the observations. Except in a few simple cases, the effect of gaps in the data on measurement precision is poorly understood, in particular in Fourier space where the convolution of the observable with the observation window introduces correlations between different frequencies. Here we describe and implement a rather general method to retrieve maximum likelihood estimates of the oscillation parameters, taking into account the proper statistics of the observations. Our fitting method applies in complex Fourier space and exploits the phase information. We consider both solar-like stochastic oscillations and long-lived harmonic oscillations, plus random noise. Using numerical simulations, we demonstrate the existence of cases for which our improved fitting method is less biased and has a greater precision than when the frequency correlations are ignored. This is especially true of low signal-to-noise solar-like oscillations. For example, we discuss a case where the precision on the mode frequency estimate is increased by a factor of five, for a duty cycle of 15%. In the case of long-lived sinusoidal oscillations, a proper treatment of the frequency correlations does not provide any significant improvement; nevertheless we confirm that the mode frequency can be measured from gapped data at a much better precision than the 1/T Rayleigh resolution.Comment: Accepted for publication in Solar Physics Topical Issue "Helioseismology, Asteroseismology, and MHD Connections

Post-release treatment uptake among participants of the Rhode Island Department of Corrections comprehensive medication assisted treatment program

The Rhode Island Department of Corrections (RIDOC) recently implemented the first state-wide, comprehensive medications for addiction treatment (MAT) program in the US. The objective of this study was to elucidate perceived barriers for individuals who participated in RIDOC's MAT program while incarcerated. Of the 588 individuals eligible for this study, 227 phone surveys were completed with 214 individuals. Data relevant to demographic characteristics, probation/parole status, retention in MAT treatment, MAT type received during incarceration, MAT treatment history, location where they received community treatment, perceived barriers to treatment, and future goals for MAT were collected. Simple percentages, frequencies, means, and standard deviations were calculated with SPSS. Most participants (82.4%) reported continuing MAT post-release and a majority (74.3%) received treatment at an opioid treatment program. Those who did not connect with treatment post-release reported transportation issues (23.1%) and not wanting to continue MAT (20.5%) as major reasons for not continuing treatment. The most commonly reported goal for treatment was to continue MAT long-term (43.5%). Results indicate that most participants linked to MAT treatment post-release. Participants reported reasons for why they did not continue MAT and had mixed intentions about continuing MAT in the future. Results provide identification of novel factors, such as side effects, time between release and treatment linkage, and family and friends' opinions that influence MAT continuation post-incarceration. Results highlight areas of exploration to influence treatment retention, including the role of probation/parole officers and the potential for peer support specialists to assist in reducing stigma and increasing interest in MAT