Astronomical seeing and ground-layer turbulence in the Canadian High Arctic

We report results of a two-year campaign of measurements, during arctic winter darkness, of optical turbulence in the atmospheric boundary-layer above the Polar Environment Atmospheric Laboratory in northern Ellesmere Island (latitude +80 deg N). The data reveal that the ground-layer turbulence in the Arctic is often quite weak, even at the comparatively-low 610 m altitude of this site. The median and 25th percentile ground-layer seeing, at a height of 20 m, are found to be 0.57 and 0.25 arcsec, respectively. When combined with a free-atmosphere component of 0.30 arcsec, the median and 25th percentile total seeing for this height is 0.68 and 0.42 arcsec respectively. The median total seeing from a height of 7 m is estimated to be 0.81 arcsec. These values are comparable to those found at the best high-altitude astronomical sites

Spatial and Temporal Variation in the Aquatic Invertebrate Community Structure of Rock Pools Along the Penobscot River, Maine

Pools of water that form in the fissures and depressions of rock outcrops, known as rock pools, are fairly common aquatic habitats that can easily be found along the rocky banks of many of Maine’s major rivers. In general, rock pools and the aquatic invertebrates inhabiting them have received little research attention and, though ubiquitous, have never been studied in Maine. My research addressed this knowledge gap by surveying 40 rock pools at four sites along the Penobscot River in Maine. The rock pools themselves had highly variable environmental characteristics and differed across sites and over time, especially in hydroperiod. They contained surprisingly abundant and diverse communities, totaling 71 invertebrate taxa across 16 orders. The non-biting midge Dicrotendipes and the biting midge Dasyhelea were the most abundant genera. Community composition differed significantly between sites in June, largely associated with differences in pool size, hydroperiod, influence of the adjacent river, and food resources. However, over the course of the summer, communities across sites became more similar to each other, likely due to the combination of phenologically-driven life histories for some taxa and the loss of stress-intolerant taxa. I also conducted an experiment in which I artificially extended rock pool hydroperiods to determine the independent effect of hydroperiod on invertebrate community structure. I hypothesized that pools with longer hydroperiods would contain more diverse and abundant invertebrate communities and that pools with longer hydroperiods would contain more long-lived taxa, such as Odonata and Coleoptera. To test this hypothesis, I prevented ten rock pools from desiccating by adding deionized water to them and left ten rock pools to naturally dry. Hydroperiod was not a significant driver of overall invertebrate abundance or richness and was only important in determining the individual abundance of one of five taxa collected in the experiment. Pool volume, location on the rock outcrop, and water chemistry (pH and conductivity) were the significant factors determining community structure. This suggests that the effect of hydroperiod observed in my survey and in other rock pool surveys may be confounded by pool size and by environmental variables mediated by hydroperiod

Computational modeling of behavior under uncertainty: Commonalities and differences between anxiety and depression

Individuals who are prone to experiencing high levels of anxiety and depression often exhibit dysfunctional behavior. For example, anxious individuals often avoid situations that have even the slightest chance of a highly negative outcome (e.g. a plane crash), and depressed individuals often show a reduced pursuit of activities that most people find enjoyable. Progress can be made in understanding dysfunctional behavior by using formal, mathematical frameworks of decision making, which break down behavior into its computational components, and in which we can start to pinpoint the specific abnormalities associated with anxiety and depression. Chapter 1.2 and 1.3 review prior literature, highlighting some of the computations that seem to be altered, such as the overestimation for the probability that rare, extremely negative events will occur. Chapter 2 and Chapter 3 empirically examine behavior in situations that require individuals to accurately estimate the probability that an outcome will (or will not) occur as a result of their actions. In a task where individuals have to estimate action-outcome probabilities by trial-and-error (Chapter 2), individuals with high overall levels of anxiety and depression show a reduced ability to align the rate at which they learn to the rate of change in the environment (i.e. the level of volatility). In a task where individuals have to choose between options that have known (risky) versus unknown (ambiguous) probabilities (Chapter 3), individuals who have high levels of physiological anxiety tend to avoid the ambiguous options more than other individuals, as information is removed about those probabilities. On the other hand, individuals who are prone to experiencing mania are more likely to make the opposite choice, seeking ambiguity, when the outcomes are rewarding. Chapter 4 examines possible sources for dysfunctional beliefs, as opposed to behaviors. In a hypothetical vocational setting where individuals estimate their rank relative to others, individuals with high levels of anhedonia-related symptoms show initial beliefs that are more negative relative to the beliefs of others. Individuals with high levels of anxiety, on the other hand, show negatively biased updating of those beliefs in response to unbiased information. Chapter 5 summarizes the empirical findings and discusses more broadly how anxiety and depression seem to impact behavior (and its underlying computations) in uncertain situations

Sub-Kolmogorov-Scale Fluctuations in Fluid Turbulence

We relate the intermittent fluctuations of velocity gradients in turbulence to a whole range of local dissipation scales generalizing the picture of a single mean dissipation length. The statistical distribution of these local dissipation scales as a function of Reynolds number is determined in numerical simulations of forced homogeneous isotropic turbulence with a spectral resolution never applied before which exceeds the standard one by at least a factor of eight. The core of the scale distribution agrees well with a theoretical prediction. Increasing Reynolds number causes the generation of ever finer local dissipation scales. This is in line with a less steep decay of the large-wavenumber energy spectra in the dissipation range. The energy spectrum for the highest accessible Taylor microscale Reynolds number R_lambda=107 does not show a bottleneck.Comment: 8 pages, 5 figures (Figs. 1 and 3 in reduced quality

Turbulent transport of material particles: An experimental study of finite size effects

We use an acoustic Lagrangian tracking technique, particularly adapted to measurements in open flows, and a versatile material particles generator (in the form of soap bubbles with adjustable size and density) to characterize Lagrangian statistics of finite sized, neutrally bouyant, particles transported in an isotropic turbulent flow of air. We vary the size of the particles in a range corresponding to turbulent inertial scales and explore how the turbulent forcing experienced by the particles depends on their size. We show that, while the global shape of the intermittent acceleration probability density function does not depend significantly on particle size, the acceleration variance of the particles decreases as they become larger in agreement with the classical scaling for the spectrum of Eulerian pressure fluctuations in the carrier flow

Spatially-Resolved Spectra of the "Teacup" AGN: Tracing the History of a Dying Quasar

The Sloan Digital Sky Survey (SDSS) Galaxy Zoo project has revealed a number of spectacular galaxies possessing Extended Emission-Line Regions (EELRs), the most famous being Hanny's Voorwerp galaxy. We present another EELR object discovered in the SDSS endeavor: the Teacup Active Galactic Nucleus (AGN), nicknamed for its EELR, which has a handle like structure protruding 15 kpc into the northeast quadrant of the galaxy. We analyze physical conditions of this galaxy with long-slit ground based spectroscopy from Lowell, Lick, and KPNO observatories. With the Lowell 1.8m Perkin's telescope we took multiple observations at different offset positions, allowing us to recover spatially resolved spectra across the galaxy. Line diagnostics indicate the ionized gas is photoionized primarily by the AGN. Additionally we are able to derive the hydrogen density from the [S II] 6716/6731 ratio. We generated two-component photoionization models for each spatially resolved Lowell spectrum. These models allow us to calculate the AGN bolometric luminosity seen by the gas at different radii from the nuclear center of the Teacup. Our results show a drop in bolometric luminosity by more than two orders of magnitude from the EELR to the nucleus, suggesting that the AGN has decreased in luminosity by this amount in a continuous fashion over 46,000 years, supporting the case for a dying AGN in this galaxy independent of any IR based evidence. We demonstrate that spatially resolved photoionization modeling could be applied to EELRs to investigate long time scale variability.Comment: 38 pages, 11 figures, accepted for publication in the Astrophysical Journa

Behavioral inhibition in childhood: European Portuguese adaptation of an observational measure (Lab-TAB)

The assessment of behaviorally inhibited children is typically based on parent or teacher reports, but this approach has received criticisms, mainly for being prone to bias. Several researchers proposed the additional use of observational methods because they provide a direct and more objective description of the child's functioning in different contexts. The lack of a laboratory assessment of temperament for Portuguese children justifies the adaptation of some episodes of the Laboratory Temperament Assessment Battery (Lab-TAB) as an observational measure for behavioral inhibition. Method: In our study, we included 124 children aged between 3 and 9 years and their parents. The evaluation of child behavioral inhibition was made by parent report (Behavioral Inhibition Questionnaire) and through Lab-TAB episodes. Parental variables with potential influence on parents’ reports were also collected using the Social Interaction and Performance Anxiety and Avoidance Scale (SIPAAS) and the Parental Overprotection Measure (POM). Results and Discussion: The psychometric analyses provided evidence that Lab-TAB is a reliable instrument and can be incorporated in a multi-method approach to assess behavioral inhibition in studies involving Portuguese-speaking children. Moderate convergence between observational and parent report measures of behavioral inhibition was obtained. Mothers’ characteristics, as well as child age, seem to significantly affect differences between measures, being potential sources of bias in the assessment of child temperament.SFRH/BD/112728/2015info:eu-repo/semantics/publishedVersio

Hydrogen masers and cesium fountains at NRC

The NRC masers H-3 and H-4 have been operating since June 1993 with cavity servo control. These low-flux active H masers are showing stabilities of about 10(exp -15) from 1 hour to several days. Stability results are presented, and the current and planned uses of the masers are discussed. A cesium fountain primary frequency standard project has been started at NRC. Trapping and launching experiments with the goal of 7 m/s launches are beginning. We discuss our plans for a local oscillator and servo that exploit the pulsed aspect of cesium fountain standards, and meet the challenge of 10(exp -14) tau(exp -1/2) stability without requiring masers. At best, we expect to run this frequency standard initially for periods of hours each working day rather than continuously for years, and so frequency transfer to outside laboratories has been carefully considered. We conclude that masers (or other even better secondary clocks) are required to exploit this potential accuracy of the cesium fountain. We present and discuss our conclusion that it is feasible to transfer frequency in this way with a transfer-induced uncertainty of less than 10(exp -15), even in the presence of maser frequency drift and random walk noise