2,465 research outputs found
Perceptions of the Desired Attributes of Practicing Physicians as Determined by Rural and Urban Physicians
Submitted to the Department of Administration, Foundations and Higher Education and the Faculty of the Graduate School of the University of Kansas in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosoph
Influence possible des protozoaires sur le taux de mortalité des bactéries autotrophes nitrifiantes
Le modĂšle de l'IAWQ du processus de boues activĂ©es reprĂ©sente les mĂ©canismes endogĂšnes de la biomasse nitrifiante par le dĂ©cĂšs des micro-organismes (Ă©quation d'ordre 1 par rapport Ă la biomasse). La constante de dĂ©cĂšs, ou taux de mortalitĂ© bA, est aujourd'hui encore mal connue, et en particulier les facteurs influants sur sa valeur. De rĂ©centes Ă©tudes ont montrĂ© que la prĂ©dation par la microfaune pourrait ĂȘtre un facteur dĂ©terminant sur la valeur de bA. Cette Ă©tude se propose donc de quantifier l'effet de la prĂ©dation sur la valeur de bA. Deux rĂ©acteurs maintenus sans alimentation en substrat ont Ă©tĂ© caractĂ©risĂ©s en parallĂšle: l'un a reçu une dose d'antibiotique spĂ©cifique aux eucaryotes (cycloheximide) afin de diminuer la quantitĂ© d'organismes de la microfaune, alors que l'autre n'a reçu aucun antibiotique (tĂ©moin). Les rĂ©sultats obtenus montrent que le cycloheximide inhibe la plupart des organismes de la microfaune sauf les amibes; celles-ci semblent plutĂŽt stimulĂ©es par cet antibiotique. En ce qui concerne la nitrification, un ralentissement de la production de nitrate dans le rĂ©acteur traitĂ© Ă l'antibiotique est observĂ© Ă partir du sixiĂšme jour. Cette diminution de production de nitrate est probablement causĂ©e par une rĂ©duction de l'azote nitrifiable (qui est mobilisĂ© par les amibes) couplĂ©e Ă une prĂ©dation des organismes nitrifiants par les amibes. D'ailleurs, l'augmentation de la prĂ©dation par les amibes Ă partir du jour 6 a diminuĂ© l'activitĂ© nitrifiante Ă©galement mesurĂ©e par respiromĂ©trie (rO2 Nmax). Cette diminution du taux de respiration indique une augmentation du taux de mortalitĂ© (bA) des organismes nitrifiants. En effet, la valeur du taux de mortalitĂ© mesurĂ©e dans le rĂ©acteur tĂ©moin est de 0.08 d-1 alors que selon la microfaune prĂ©sente dans le rĂ©acteur inhibĂ© au cycloheximide, la valeur de ce taux de mortalitĂ© a variĂ© entre 0.05 d-1 et 0.15 d-1.Designing biological wastewater treatment plants with the aid of the model developed by the IAWQ requires the knowledge of biological kinetic parameters. For nitrifying activated sludge, these parameters are related to nitrifying bacteria: maximum autotrophic growth rate ”Amax, yield coefficient YA and the autotrophic decay rate bA. Although variables influencing ”Amax and YA values are well known, this is not the case for bA. MARTINAGE and PAUL (2000) have recently shown that the bA value is strongly influenced by the influent quality, leading to the assumption that influent quality has a strong effect on microfauna composition, and consequently on the grazing rate of microfauna on nitrifying bacteria. In fixed-film processes, protozoan grazing reduces the bacterial population considerably (NATUSCKA and WELANDER, 1994). However, although many data are available concerning the grazing rates of different protozoa, the effect of microfaunal grazing on nitrification is still a matter of debate (RATSAK et al., 1994) and its effect on the bA value is still unknown. These two topics are investigated here.Nitrifying activated sludges were grown in two identical batch reactors, but in one, cycloheximide was added to inhibit eucaryotic growth (MAURINES CARBONEILL et al., 1998). Microfauna organism numbers were quantified in both reactors by microscopic observations of flagellated protozoa (>8 ”m), amoebae, ciliates, rotifers and higher invertebrates (Fig. 3). Microbial counts were then correlated with the bA value. The latter was determined using the procedure proposed by SALZER (1992) which consists of characterising the time behaviour of the maximum nitrification rate measured by respirometry of activated sludge under substrate starvation. Under these conditions bacteria die and organic nitrogen is released into the bulk phase. This nitrogen is ammonified, and nitrifying bacteria use this substrate to produce nitrate, and then autotrophic bacterial growth occurs. This method takes this growth into account by characterising nitrate production during the experiment (Fig. 2).The effect of cycloheximide on nitrification was first determined to make sure that this compound is not inhibitory toward nitrifiers. Results obtained (Table 1) show that cycloheximide was not inhibitory toward nitrate production or the maximum nitrification oxygen uptake rate (rO2 N) after 4 hours of contact with nitrifying biomass. Cycloheximide addition in the activated sludge had an important impact on rotifers and flagellates but no effect on ciliates; it also seemed to stimulate amoebae growth. In both reactors, flagellates were mainly Peranama, attached ciliates were mainly Opercularia and Epistylis and a few Vorticella. Free ciliates like Aspidisca and Euplotes were found in both reactors.Variation with time of the abundance of microfauna organisms is shown in Figures 4 and 5 for both reactors. In the reference reactor the number of microfauna organisms decreased with time (Fig. 4) probably due to substrate starvation. Microfauna composition remained however diversified. For the inhibited reactor (Fig. 5), three periods were observed. During period I, the microfauna was mainly composed of ciliates and the number of microfaunal organisms decreased rapidly. During period II, an important growth of amoebae was observed. Cycloheximide was then added during this period to reduce their number. This growth of amoebae seems to be caused by the resistance of these micro-organisms toward inhibiting compounds (SRIKANTH et BERK, 1993). During period III, the number of microfaunal organisms was lower than during period II, and microfauna was mainly composed of ciliates.Nitrate concentration behaviour, necessary for bA calculation, is shown on Figure 6. In the reference reactor, nitrate concentrations varied linearly. For the inhibited reactor, the linear pattern was not observed during period II. This result was probably caused by an important nitrogen assimilation need of amoebae (ELDRIGE and JACKSON, 1993). Because organic nitrogen released by bacterial decay is consumed by amoebae assimilation, less nitrogen is available for the ammonification process and therefore for nitrification. Ammonia concentrations remained below 0.2 mg N·l-1 during all the experiment for both reactors. When amoebae disappeared from the inhibited reactor (period III) nitrate concentration varied linearly again.Variations of the maximum nitrification oxygen uptake rate (rO2 Nmax) with time are presented in Figure 7 (A&B) for both reactors. Two curves are plotted on each figure. Empty squares represent the measured rO2 N and black points represent the maximum nitrification rate that would have been measured if no growth on ammonification products had occurred. For the reference reactor (Fig. 7A), a value for bA of 0.08 d-1 can be calculated and can be considered constant for a constant microfauna composition.Three bA values can be estimated for the reactor inhibited with cycloheximide (Fig. 7B), corresponding to the three periods observed for microfauna composition. During period I, the bA value is 0.05 d-1 : a decrease in the microfaunal organism numbers implies a decrease of the bA value. During period II, when a development of amoebae is observed, the bA value increases and reaches 0.15 d-1. During period III with reduced grazing, the bA value is 0.13 d-1. Since during periods I and III the microfauna is mainly composed of ciliates, this difference between bA values is likely due to the observed difference in floc size between periods I and III.The results obtained during this study tend to prove (1) that the use of cycloheximide reduces microfaunal populations but can lead to a development of amoebae, and (2) that microfauna grazing seems to have an influence on the bA value, which can vary from 0.05 to 0.15 d-1 depending on microfaunal composition and abundance
Worrisome Properties of Neural Network Controllers and Their Symbolic Representations
We raise concerns about controllers' robustness in simple reinforcement
learning benchmark problems. We focus on neural network controllers and their
low neuron and symbolic abstractions. A typical controller reaching high mean
return values still generates an abundance of persistent low-return solutions,
which is a highly undesirable property, easily exploitable by an adversary. We
find that the simpler controllers admit more persistent bad solutions. We
provide an algorithm for a systematic robustness study and prove existence of
persistent solutions and, in some cases, periodic orbits, using a
computer-assisted proof methodology.Comment: accepted to ECAI2
Large-Scale Aspects and Temporal Evolution of Pulsating Aurora
Pulsating aurora is a common phenomenon generally believed to occur mainly in the aftermath of a, substorm, where dim long-period pulsating patches appear. The study determines the temporal and spatial evolution of pulsating events using two THEN IIIS ASI stations, at Gillam (66.18 mlat, 332.78 mlon, magnetic midnight at 0634 UT) and Fort Smith, (67.38 mlat, 306.64 mlon, magnetic midnight at, 0806 UT) along roughly the same invariant latitude. Parameters have been calculated from a database of 74 pulsating aurora events from 119 days of good optical data within the period from September 2007 through March 2008 as identified with the Gillam camera. It is shown that the source region of pulsating aurora drifts or expands eastward, away from magnetic midnight, for pre-midnight onsets and that the spatial evolution is more complicated for post midnight onsets, which has implications for the source mechanism. The most probable duration of a pulsating aurora event is roughly 1.5 hours while the distribution of possible event durations includes many long (several hours) events. This may suggest that pulsating aurora is not strictly a substorm recovery phase phenomenon but rather a persistent, long-lived phenomenon that may be temporarily disrupted by auroral substorms. Observations from the Gillam station show that in fact, pulsating aurora is quite common with the occurrence rate increasing to around 60% for morning hours, with 6910 of pulsating aurora onsets occurring after substorm breakup
Aspects of topology of condensates and knotted solitons in condensed matter systems
The knotted solitons introduced by Faddeev and Niemi is presently a subject
of great interest in particle and mathematical physics. In this paper we give a
condensed matter interpretation of the recent results of Faddeev and Niemi.Comment: v2: Added a reference to the paper E. Babaev, L.D. Faddeev and A.J.
Niemi cond-mat/0106152 where an exact equivalence was shown between the
two-condensate Ginzburg-Landau model and a version of Faddeev model.
Miscelaneous links related to knotted solitons are available at the author
homepage at http://www.teorfys.uu.se/PEOPLE/egor/ . Animations of knotted
solitons by Hietarinta and Salo are available at
http://users.utu.fi/h/hietarin/knots/c45_p2.mp
A study of Pc-5 ULF oscillations
International audienceA study of Pc-5 magnetic pulsations using data from the Combined Release and Radiation Effects Satellite (CRRES) was carried out. Three-component dynamic magnetic field spectrograms have been used to survey ULF pulsation activity for the approximate fourteen month lifetime of CRRES. Two-hour panels of dynamic spectra were examined to find events which fall into two basic categories: 1) toroidal modes (fundamental and harmonic resonances) and 2) poloidal modes, which include compressional oscillations. The occurence rates were determined as a function of L value and local time. The main result is a comparable probability of occurence of toroidal mode oscillations on the dawn and dusk sides of the magnetosphere inside geosynchronous orbit, while poloidal mode oscillations occur predominantly along the dusk side, consistent with high azimuthal mode number excitation by ring current ions. Pc-5 pulsations following Storm Sudden Commencements (SSCs) were examined separately. The spatial distribution of modes for the SSC events was consistent with the statistical study for the lifetime of CRRES. The toroidal fundamental (and harmonic) resonances are the dominant mode seen on the dawn-side of the magnetosphere following SSCs. Power is mixed in all three components. In the 21 dusk side SSC events there were only a few examples of purely compressional (two) or radial (one) power in the CRRES study, a few more examples of purely toroidal modes (six), with all three components predominant in about half (ten) of the events. Key words. Magnetospheric physics (MHD waves and instabilities; magnetospheric configuration and dynamics) ? Space plasma physics (waves and instabilities
Context Matters: A Theory of Semantic Discriminability for Perceptual Encoding Systems
People's associations between colors and concepts influence their ability to
interpret the meanings of colors in information visualizations. Previous work
has suggested such effects are limited to concepts that have strong, specific
associations with colors. However, although a concept may not be strongly
associated with any colors, its mapping can be disambiguated in the context of
other concepts in an encoding system. We articulate this view in semantic
discriminability theory, a general framework for understanding conditions
determining when people can infer meaning from perceptual features. Semantic
discriminability is the degree to which observers can infer a unique mapping
between visual features and concepts. Semantic discriminability theory posits
that the capacity for semantic discriminability for a set of concepts is
constrained by the difference between the feature-concept association
distributions across the concepts in the set. We define formal properties of
this theory and test its implications in two experiments. The results show that
the capacity to produce semantically discriminable colors for sets of concepts
was indeed constrained by the statistical distance between color-concept
association distributions (Experiment 1). Moreover, people could interpret
meanings of colors in bar graphs insofar as the colors were semantically
discriminable, even for concepts previously considered "non-colorable"
(Experiment 2). The results suggest that colors are more robust for visual
communication than previously thought.Comment: To Appear in IEEE Transactions on Visualization and Computer Graphic
Periodic orbits in HoĆavaâLifshitz cosmologies
We consider spatially homogeneous HoĆavaâLifshitz models that perturb General Relativity (GR) by a parameter vâ(0,1) such that GR occurs at v=1/2. We describe the dynamics for the extremal case v=0, which possess the usual Bianchi hierarchy: type I (Kasner circle of equilibria), type II (heteroclinics that induce the Kasner map) and type VI0,VII0 (further heteroclinics). For type VIII and IX, we use a computer-assisted approach to prove the existence of periodic orbits which are far from the Mixmaster attractor. Therefore we obtain a new behaviour which is not described by the BKL picture of bouncing Kasner-like states
A novel physiological role for ARF1 in the formation of bidirectional tubules from the Golgi.
Capitalizing on CRISPR/Cas9 gene-editing techniques and super-resolution nanoscopy, we explore the role of the small GTPase ARF1 in mediating transport steps at the Golgi. Besides its well-established role in generating COPI vesicles, we find that ARF1 is also involved in the formation of long (âŒ3 ”m), thin (âŒ110 nm diameter) tubular carriers. The anterograde and retrograde tubular carriers are both largely free of the classical Golgi coat proteins coatomer (COPI) and clathrin. Instead, they contain ARF1 along their entire length at a density estimated to be in the range of close packing. Experiments using a mutant form of ARF1 affecting GTP hydrolysis suggest that ARF1[GTP] is functionally required for the tubules to form. Dynamic confocal and stimulated emission depletion imaging shows that ARF1-rich tubular compartments fall into two distinct classes containing 1) anterograde cargoes and clathrin clusters or 2) retrograde cargoes and coatomer clusters
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