1,233 research outputs found
CPN Tools 4: Multi-formalism and Extensibility
Abstract. CPN Tools is an advanced tool for editing, simulating, and analyzing colored Petri nets. This paper discusses the fourth major re-lease of the tool, which makes it simple to use the tool for ordinary Petri nets, including adding inhibitor and reset arcs, and PNML export. This version also supports declarative modeling using constraints, and adds an extension framework making it easy for third parties to extend CPN Tools using Java.
The Impact of Workplace Conditions on Firm Performance
This paper estimates the impact of work environment health and safety practice on firm performance, and examines which firm-characteristic factors are associated with good work conditions. We use Danish longitudinal register matched employer-employee data, merged with firm business accounts and detailed cross-sectional survey data on workplace conditions. This enables us to address typical econometric problems such as omitted variables bias or endogeneity in estimating i) standard production functions augmented with work environment indicators and aggregate employee characteristics and ii) firm mean wage regressions on the same explanatory variables. Our findings suggest that improvement in some of the physical dimensions of the work health and safety environment (specifically, âinternal climateâ and ârepetitive and strenuous activityâ) strongly impacts the firm productivity, whereas âinternal climateâ problems are the only workplace hazards compensated for by higher mean wages
Ultrastable lasers based on vibration insensitive cavities
We present two ultra-stable lasers based on two vibration insensitive cavity
designs, one with vertical optical axis geometry, the other horizontal.
Ultra-stable cavities are constructed with fused silica mirror substrates,
shown to decrease the thermal noise limit, in order to improve the frequency
stability over previous designs. Vibration sensitivity components measured are
equal to or better than 1.5e-11 per m.s^-2 for each spatial direction, which
shows significant improvement over previous studies. We have tested the very
low dependence on the position of the cavity support points, in order to
establish that our designs eliminate the need for fine tuning to achieve
extremely low vibration sensitivity. Relative frequency measurements show that
at least one of the stabilized lasers has a stability better than 5.6e-16 at 1
second, which is the best result obtained for this length of cavity.Comment: 8 pages 12 figure
Psychosocial work environment and antidepressant medication: a prospective cohort study
<p>Abstract</p> <p>Background</p> <p>Adverse psychosocial work environments may lead to impaired mental health, but it is still a matter of conjecture if demonstrated associations are causal or biased. We aimed at verifying whether poor psychosocial working climate is related to increase of redeemed subscription of antidepressant medication.</p> <p>Methods</p> <p>Information on all antidepressant drugs (AD) purchased at pharmacies from 1995 through 2006 was obtained for a cohort of 21,129 Danish public service workers that participated in work climate surveys carried out during the period 2002â2005. Individual self-reports of psychosocial factors at work including satisfaction with the work climate and dimensions of the job strain model were obtained by self-administered questionnaires (response rate 77,2%). Each employee was assigned the average score value for all employees at his/her managerial work unit [1094 units with an average of 18 employees (range 3â120)]. The risk of first-time AD prescription during follow-up was examined according to level of satisfaction and psychosocial strain by Cox regression with adjustment for gender, age, marital status, occupational status and calendar year of the survey.</p> <p>Results</p> <p>The proportion of employees that received at least one prescription of ADs from 1995 through 2006 was 11.9% and prescriptions rose steadily from 1.50% in 1996 to the highest level 6.47% in 2006. ADs were prescribed more frequent among women, middle aged, employees with low occupational status and those living alone. None of the measured psychosocial work environment factors were consistently related to prescription of antidepressant drugs during the follow-up period.</p> <p>Conclusion</p> <p>The study does not indicate that a poor psychosocial work environment among public service employees is related to prescription of antidepressant pharmaceuticals. These findings need cautious interpretation because of lacking individual exposure assessments.</p
Ultraviolet Absorption Spectra at Reduced Temperatures. I. Principles and Methods
Low temperature absorption and fluorescence spectra of solids, liquids,
and solutions often reveal increased spectral detail of use in analytical
procedures and molecular structure studies. Nevertheless, while qualitative
observations of the influence of liquid air temperatures upon optical
properties were undertaken very early, investigations of the
absorption and fluorescence of organic compounds at the temperature
of liquid nitrogen (-195.6°; 77.4 °K.) and below have appeared only
sporadically. Because of the potential usefulness of the technique we have undertaken a systematic study of the low temperature spectra
of substances of biochemical interest. The present paper discusses the
methods employed; subsequent papers will deal with the experimental
results. In this work, we have emphasized the wave-length location of
absorption bands and the accurate determination of relative optical densities
rather than precision in the determination of absolute optical densities,
thus permitting the use of simpler methods than would otherwise be
necessary
Moving out of town? The status of alien plants in highâArctic Svalbard, and a method for monitoring of alien flora in highârisk, polar environments
Abstract Rising human activity in the Arctic, combined with a warming climate, increases the probability of introduction and establishment of alien plant species. While settlements are known hotspots for persistent populations, little is known about colonization of particularly susceptible natural habitats. Systematic monitoring is lacking and available survey methods vary greatly. Here, we present the most comprehensive survey of alien vascular plant species in the highâArctic archipelago of Svalbard to date, aimed at (i) providing a status within settlements; (ii) surveying highârisk habitats such as those with high visitor numbers and nutrient enrichment from sea bird colonies; (iii) presenting a systematic monitoring method that can be implemented in future work on alien plant species in Arctic environments; and (iv) discuss possibilities for mapping alien plant habitats using unmanned aerial vehicles. The systematic grid survey, covering 1.7Â km2 over three settlements and six bird cliffs, detected 36 alien plant species. Alien plant species were exclusively found in areas of human activity, particularly areas associated with current or historic animal husbandry. The survey identified the successful eradication of Anthriscus sylvestris in Barentsburg, as well as the rapid expansion of Taraxacum sect. Ruderalia over the last few decades. As there is currently no consistent method for monitoring alien plant species tailored to polar environments, we propose a systematic methodology that could be implemented within a structured monitoring regime as part of an adaptive monitoring strategy towards alien species in the Arctic
Experimenting an optical second with strontium lattice clocks
Progress in realizing the SI second had multiple technological impacts and
enabled to further constraint theoretical models in fundamental physics.
Caesium microwave fountains, realizing best the second according to its current
definition with a relative uncertainty of 2-4x10^(-16), have already been
superseded by atomic clocks referenced to an optical transition, both more
stable and more accurate. Are we ready for a new definition of the second? Here
we present an important step in this direction: our system of five clocks
connects with an unprecedented consistency the optical and the microwave
worlds. For the first time, two state-of-the-art strontium optical lattice
clocks are proven to agree within their accuracy budget, with a total
uncertainty of 1.6x10^(-16). Their comparison with three independent caesium
fountains shows a degree of reproducibility henceforth solely limited at the
level of 3.1x10^(-16) by the best realizations of the microwave-defined second.Comment: 9 pages, 4 figures, 2 table
Calibration of the NuSTAR High Energy Focusing X-ray Telescope
We present the calibration of the \textit{Nuclear Spectroscopic Telescope
Array} (\nustar) X-ray satellite. We used the Crab as the primary effective
area calibrator and constructed a piece-wise linear spline function to modify
the vignetting response. The achieved residuals for all off-axis angles and
energies, compared to the assumed spectrum, are typically better than \%
up to 40\,keV and 5--10\,\% above due to limited counting statistics. An
empirical adjustment to the theoretical 2D point spread function (PSF) was
found using several strong point sources, and no increase of the PSF half power
diameter (HPD) has been observed since the beginning of the mission. We report
on the detector gain calibration, good to 60\,eV for all grades, and discuss
the timing capabilities of the observatory, which has an absolute timing of
3\,ms. Finally we present cross-calibration results from two campaigns
between all the major concurrent X-ray observatories (\textit{Chandra},
\textit{Swift}, \textit{Suzaku} and \textit{XMM-Newton}), conducted in 2012 and
2013 on the sources 3C\,273 and PKS\,2155-304, and show that the differences in
measured flux is within 10\% for all instruments with respect to \nustar
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