Entity

Time filter

Source Type

Märstetten-Dorf, Switzerland

Feller U.,Federal Office of Metrology METAS
Accreditation and Quality Assurance | Year: 2011

The International System of Units (SI) follows a concept that goes back to Maxwell. At that time, a logic sound foundation of mathematics was not yet available. This has lead to concepts and terms that are contradictory and in conflict with today's standard mathematical concepts. The inconsistencies that have evolved in metrology due to the lack of appropriate notions are pointed out. This is most important, as the metrology is a field that is internationally well organized under the umbrella of the Meter Convention, an international treaty for acting on all matters relating to units of measurement. Committees and working groups under the Meter Convention have a leading role in the elaboration of important metrological guides, among others the International Vocabulary of Metrology. Therefore, it is highly desirable that their publications use well-founded concepts and terminology. It is consensus that it is desirable to find a system of units on invariant properties of nature and not on human artifacts, e.g., the prototype of the kilogram. However, the current proposals to improve that are in conflict with standard scientific concepts. It is shown in the paper how these inconsistencies can be avoided. The argumentation is based on the interpretation of numbers developed by mathematicians like Cantor, Dedekind, Peano, and others that have led the logic foundation of mathematics with set and number theory. This foundation excludes dogmas that have been forwarded in the last century under the umbrella of the Meter Convention. © 2011 The Author(s). Source


Marty P.T.,University of Bern | Morel J.,Federal Office of Metrology METAS | Feurer T.,University of Bern
Optics Express | Year: 2010

We present an all-fiber frequency-stabilized ring laser system with an integrated reference gas cell consisting of a hollow core fiber filled with acetylene. Through nonlinear absorption spectroscopy the laser frequency is stabilized to a specific absorption line of acetylene. Three different stabilization schemes are investigated and the minimum Allan deviation obtained after 100 s is 4.4 .10-11. © 2010 Optical Society of America. Source


Marty P.T.,University of Bern | Morel J.,Federal Office of Metrology METAS | Feurer T.,University of Bern
Journal of Lightwave Technology | Year: 2010

We demonstrate a multi-purpose all-fiber design for gas-filled cavities based on hollow core photonic crystal fibers and on a specially designed fiber connector system. The connector system allows to evacuate and to fill the fiber core with a gaseous medium and keeping it pressure-tight. It also allows connecting the hollow core fiber to standard fibers. We demonstrate the flexibility and functionality by realizing three different all-fiber spectroscopic devices. Firstly, a single pass gas cell for linear absorption spectroscopy, secondly, a double pass gas cell and, thirdly, an all-fiber FabryPerot cavity for nonlinear saturation spectroscopy. © 2010 IEEE. Source


Chellappa S.L.,University of Basel | Steiner R.,University of Basel | Blattner P.,Federal Office of Metrology METAS | Oelhafen P.,University of Basel | And 2 more authors.
PLoS ONE | Year: 2011

Background: Light exposure can cascade numerous effects on the human circadian process via the non-imaging forming system, whose spectral relevance is highest in the short-wavelength range. Here we investigated if commercially available compact fluorescent lamps with different colour temperatures can impact on alertness and cognitive performance. Methods: Sixteen healthy young men were studied in a balanced cross-over design with light exposure of 3 different light settings (compact fluorescent lamps with light of 40 lux at 6500K and at 2500K and incandescent lamps of 40 lux at 3000K) during 2 h in the evening. Results: Exposure to light at 6500K induced greater melatonin suppression, together with enhanced subjective alertness, well-being and visual comfort. With respect to cognitive performance, light at 6500K led to significantly faster reaction times in tasks associated with sustained attention (Psychomotor Vigilance and GO/NOGO Task), but not in tasks associated with executive function (Paced Visual Serial Addition Task). This cognitive improvement was strongly related with attenuated salivary melatonin levels, particularly for the light condition at 6500K. Conclusions: Our findings suggest that the sensitivity of the human alerting and cognitive response to polychromatic light at levels as low as 40 lux, is blue-shifted relative to the three-cone visual photopic system. Thus, the selection of commercially available compact fluorescent lights with different colour temperatures significantly impacts on circadian physiology and cognitive performance at home and in the workplace. © 2011 Chellappa et al. Source


Thomas Marty P.,University of Bern | Morel J.,Federal Office of Metrology METAS | Feurer T.,University of Bern
Optics Letters | Year: 2011

We investigate the dynamics of an erbium-doped fiber ring laser that is equipped with an intracavity hollow core photonic crystal fiber gas cell. The cell is filled with acetylene as a saturable absorber. We observe cw operation at low pressures, Q switching at intermediate pressure levels, and mode locking at high pressures applied. Moreover, we show that the transition from the cw to the pulsed mode may be exploited for sensitive gas detection. © 2011 Optical Society of America. Source

Discover hidden collaborations