Sea glider guidance around a circle using distance measurements to a drifting acoustic source

International audienceThis paper describes a simple yet robust sea glider guidance method in a constellation of Lagrangian drifters under the polar ice cap. The glider has to perform oceanographic measurements, mainly conductivity, temperature and depth, in the area enclosed by the drifters and can not rely on GNSS (Global Navigation Satellite System) positionning data as the polar ice cap makes it impossible to surface. The originality of the presented method resides in 2 points. First, a very simple PID (Proportional, Integral and Derivative) controller based on a basic kinematic model is tuned. Second, the method does not use a localization algorithm to estimate state space model data but interval analysis methods are performed to bound the errors in range to the transponder and its derivative. Moreover, only one acoustic beacon is used. Validation is then performed through simulations

Capital Expenditure Decisions and the Role of the Not-for-Profit Hospital: An Application of a Social Goods Model

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68370/2/10.1177_107755879004700404.pd

Does employee happiness have an impact on productivity?

This article provides quasi-experimental evidence on the relationship between employee happiness and productivity in the field. We study the universe of call center sales workers at British Telecom (BT), one of the United Kingdom's largest private employers. We measure their happiness over a 6 month period using a novel weekly survey instrument, and link these reports with highly detailed administrative data on workplace behaviors and various measures of employee performance. Exploiting exogenous variation in employee happiness arising from weather shocks local to each of the 11 call centers, we document a strong causal effect of worker happiness on sales. This is driven by employees working more effectively on the intensive margin by making more calls per hour, adhering more closely to their workflow schedule, and converting more calls into sales when they are happier. In our restrictive setting, we find no effects on the extensive margin of happiness on various measures of high-frequency labor supply such as attendance and break-takin

Afval van schoenlappers/oud-schoenmakers en versleten schoeisel uit Ninove (prov. Oost-Vlaanderen)

De klemtoon van deze bijdrage ligt op de studie van een hoeveelheid leerresten aangetroffen op de Ninoofse Graanmarkt naar aanleiding van grootschalige infrastructuurwerken in 2009. Ninove is gelegen in het zuidoosten van de provincie Oost-Vlaanderen in de Dendervallei. De Graanmarkt zelf situeert zich op de westelijke flank van de vallei en wordt omsloten door een historische Denderarm in het zuiden en een bijriviertje van de Dender, de thans overwelfde Beverbeek, in het noorden en het oosten. Enkel de westelijke helft van de markt valt samen met de historische Graanmarkt. Het oostelijke deel van het huidige marktplein vormde in de middeleeuwen de Varkensmarkt. Een groot deel van de Graanmarkt werd ingenomen door de graanhal waarvan de oudste vermelding teruggaat tot 1334. Hoewel in de graanhal in hoofdzaak graan werd gestockeerd en laken verhandeld, waren dit niet de enige activiteiten die er plaatsvonden. Vanaf 1367 werd er ook recht gesproken en in de 18de en 19de eeuw gebruikten soldaten haar als verblijfplaats en fungeerde ze als opslagruimte voor hooi en stro. Tegen het midden van de 19de eeuw zou de graanhal volledig uit het straatbeeld verdwenen zijn.Het onderzoek leverde in totaal 10 kuilen op waarin leervondsten voorkwamen. In totaal gaat het bij deze collectie om 840 fragmenten leer. De verschillende leercontexten reiken wat dateringsgegevens betreft slechts in beperkte mate informatie aan. De twee grootste contexten kunnen op basis van technische en morfologische gegevens van de hierin aangetroffen schoenresten slechts breed gedateerd worden in de late 14de - 15de eeuw. Het specifieke afval in beide kuilen wijst op de activiteiten van schoenlappers/oud-schoenmakers. Meer specifiek gaat het hierbij om het afval dat ontstond tijdens het lappen of repareren van versleten schoenen waarmee de klanten naar de markt kwamen en/of de leerresten van het oud-schoenmaken op de markt. Het afval dat hierbij ontstond werd in een kuil op de markt zelf gedumpt. De leerresten uit de reeks kuilen op de Graanmarkt moeten eerder geïnterpreteerd worden als de restanten van weggegooid, versleten schoeisel dat voornamelijk in de 17de en 18de eeuw moet gedateerd worden

Generalized changes of benthic communities after construction of wind farms in the southern North Sea

Over the last years, the development of offshore renewable energy installations such as offshore wind farms led to an increasing number of man-made structures in marine environments. Since 2009, benthic impact monitoring programs were carried out in wind farms installed in the southern North Sea. We collated and analyzed data sets from three major monitoring programs. Our analysis considered a total of 2849 sampling points converted to a set of biodiversity response metrics. We analyzed biodiversity changes related to the implementation of offshore wind farms and generalized the correlation of these changes with spatial and temporal patterns. Our results demonstrate that depth, season and distance to structure (soft-bottom community) consistently determined diversity indicators and abundance parameters, whereas the age and the country affiliation were significantly related to some but not all indices. The water depth was the most important structuring factor for fouling communities while seasonal effects were driving most of the observed changes in soft-sediment communities. We demonstrate that a meta-analysis can provide an improved level of understanding of ecological patterns on largescale effects of anthropogenic structures on marine biodiversity, which were not visible in single monitoring studies. We believe that meta-analyses should become an indispensable tool for management of offshore wind farm effects in the future, particularly in the view of the foreseen development of offshore renewable energies. This might lead to a better picture and more comprehensive view on potential alterations. However, this requires a modern open-source data policy and data management, across institutions and across national borders

A unified censored normal regression model for qPCR differential gene expression analysis

Reverse transcription quantitative polymerase chain reaction (RT-qPCR) is considered as the gold standard for accurate, sensitive, and fast measurement of gene expression. Prior to downstream statistical analysis, RT-qPCR fluorescence amplification curves are summarized into one single value, the quantification cycle (Cq). When RT-qPCR does not reach the limit of detection, the Cq is labeled as undetermined . Current state of the art qPCR data analysis pipelines acknowledge the importance of normalization for removing non-biological sample to sample variation in the Cq values. However, their strategies for handling undetermined Cq values are very ad hoc. We show that popular methods for handling undetermined values can have a severe impact on the downstream differential expression analysis. They introduce a considerable bias and suffer from a lower precision. We propose a novel method that unites preprocessing and differential expression analysis in a single statistical model that provides a rigorous way for handling undetermined Cq values. We compare our method with existing approaches in a simulation study and on published microRNA and mRNA gene expression datasets. We show that our method outperforms traditional RT-qPCR differential expression analysis pipelines in the presence of undetermined values, both in terms of accuracy and precision

The costs and benefits of estimating T-1 of tissue alongside cerebral blood flow and arterial transit time in pseudo-continuous arterial spin labeling

Multi-post-labeling-delay pseudo-continuous arterial spin labeling (multi-PLD PCASL) allows for absolute quantification of the cerebral blood flow (CBF) as well as the arterial transit time (ATT). Estimating these perfusion parameters from multi-PLD PCASL data is a non-linear inverse problem, which is commonly tackled by fitting the single-compartment model (SCM) for PCASL, with CBF and ATT as free parameters. The longitudinal relaxation time of tissue T-1t is an important parameter in this model, as it governs the decay of the perfusion signal entirely upon entry in the imaging voxel. Conventionally, T-1t is fixed to a population average. This approach can cause CBF quantification errors, as T-1t can vary significantly inter- and intra-subject. This study compares the impact on CBF quantification, in terms of accuracy and precision, of either fixing T-1t, the conventional approach, or estimating it alongside CBF and ATT. It is shown that the conventional approach can cause a significant bias in CBF. Indeed, simulation experiments reveal that if T-1t is fixed to a value that is 10% off its true value, this may already result in a bias of 15% in CBF. On the other hand, as is shown by both simulation and real data experiments, estimating T-1t along with CBF and ATT results in a loss of CBF precision of the same order, even if the experiment design is optimized for the latter estimation problem. Simulation experiments suggest that an optimal balance between accuracy and precision of CBF estimation from multi-PLD PCASL data can be expected when using the two-parameter estimator with a fixed T-1t value between population averages of T-1t and the longitudinal relaxation time of blood T-1b

Forming Circumbinary Planets: N-body Simulations of Kepler-34

Observations of circumbinary planets orbiting very close to the central stars have shown that planet formation may occur in a very hostile environment, where the gravitational pull from the binary should be very strong on the primordial protoplanetary disk. Elevated impact velocities and orbit crossings from eccentricity oscillations are the primary contributors towards high energy, potentially destructive collisions that inhibit the growth of aspiring planets. In this work, we conduct high resolution, inter-particle gravity enabled N-body simulations to investigate the feasibility of planetesimal growth in the Kepler-34 system. We improve upon previous work by including planetesimal disk self-gravity and an extensive collision model to accurately handle inter-planetesimal interactions. We find that super-catastrophic erosion events are the dominant mechanism up to and including the orbital radius of Kepler-34(AB)b, making in-situ growth unlikely. It is more plausible that Kepler-34(AB)b migrated from a region beyond 1.5 AU. Based on the conclusions that we have made for Kepler-34 it seems likely that all of the currently known circumbinary planets have also migrated significantly from their formation location with the possible exception of Kepler-47(AB)c.Comment: 6 pages, 5 figures, accepted for publication in ApJ