917 research outputs found
Mechanistische Untersuchung der in Acrylsäure ablaufenden Prozesse
Acrylsäure besitzt eine hohe Reaktivität, welche sich zur Herstellung von einer Vielzahl an Produkten
eignet, jedoch Probleme beim Transport und bei der Lagerung verursacht. Hierbei tritt durch die Alterung ein Qualitätsverlust ein, weshalb in dieser Arbeit zunächst die Nebenproduktbildung in reiner Acrylsäure und in wässrigen Acrylsäuremischungen untersucht wird. Hierzu werden die Konzentrationsverläufe der Komponenten Acrylsäure (AA), Diacrylsäure (DiAA), Triacrylsäure (TriAA), 3-Hydroxypropionsäure (3-HPA) und 3-Hydroxydiacrylsäure (3-HDiAA) ermittelt. Diese Konzentrationsverläufe werden mit den vorgestellten Reaktionswegen modelliert. Weiterhin ist die Neigung zur unerwünschten Polymerisation von Acrylsäure ein erhebliches Problem bei falscher Lagerung, welche zu einem Runaway führen kann. Deshalb wird in dieser Arbeit die Effektivität und Wirkungsweise eines Restabilisator-Gemisches untersucht. Hierzu werden unterschiedliche Szenarien der Restabilisierung durchgeführt und dabei die eingesetzte Menge an Restabilisator variiert. Aus den Ergebnissen werden Sicherheitsdiagramme erstellt, mit deren Hilfe die zur Restabilisierung benötigte Menge ermittelt werden kann
Direct laser-written optomechanical membranes in fiber Fabry-Perot cavities
Integrated micro and nanophotonic optomechanical experiments enable the
manipulation of mechanical resonators on the single phonon level. Interfacing
these structures requires elaborate techniques limited in tunability,
flexibility, and scaling towards multi-mode systems. Here, we demonstrate a
cavity optomechanical experiment using 3D-laser-written polymer membranes
inside fiber Fabry-Perot cavities. Vacuum coupling strengths of ~ 30 kHz to the
fundamental megahertz mechanical mode are reached. We observe optomechanical
spring tuning of the mechanical resonator by tens of kHz exceeding its
linewidth at cryogenic temperatures. The extreme flexibility of the laser
writing process allows for a direct integration of the membrane into the
microscopic cavity. The direct fiber coupling, its scaling capabilities to
coupled resonator systems, and the potential implementation of dissipation
dilution structures and integration of electrodes make it a promising platform
for fiber-tip integrated accelerometers, optomechanically tunable multi-mode
mechanical systems, or directly fiber-coupled systems for microwave to optics
conversion.Comment: 10 pages, 5 figure
How to Measure the Mental Health of Teachers? Psychometric Properties of the GHQ-12 in a Large Sample of German Teachers.
To improve the health status of teachers, there is a need for good and reliable instruments to continuously assess their mental health. The current study proposed the GHQ-12 questionnaire as an appropriate instrument for measuring the mental health of teachers. The GHQ-12 is a well-established screening instrument that has mostly been applied in non-teaching samples. In the current study, the psychometric properties of the questionnaire were analyzed using a large sample of German teachers (N = 3996). The data was collected yearly over an extended period of time (2012-2020). Results showed good to very good reliability, as well as high correspondence to burnout and life satisfaction scales. Principal axis factor analysis supported a two-factor structure: Factor 1 represents "depression/stress" and Factor 2 represents "loss of confidence". However, the mental health of the investigated teachers was worse than that of a representative sample in Germany. Consequently, this study highlighted the fact that the teaching profession is vulnerable to mental strain and underlined the importance of promoting prevention programs that could help to sustain and foster the mental health of teachers. In this context, the GHQ-12 could be proposed as a good and economic tool to assess and analyze mental health in German teachers. The presented norm could help practitioners and teachers to compare individual scores within a larger peer group
Flexible experimental platform for dispersion-free temporal characterization of ultrashort pulses
The precise temporal characterization of laser pulses is crucial for
ultrashort applications in biology, chemistry, and physics. Especially in
femto- and attosecond science, diverse laser pulse sources in different
spectral regimes from the visible to the short-wavelength infrared as well as
pulse durations ranging from picoseconds to few femtoseconds are employed. In
this article, we present a versatile temporal-characterization apparatus that
can access these different temporal and spectral regions in a dispersion-free
manner and without phase-matching constraints. The design combines
transient-grating and surface third-harmonic-generation frequency-resolved
optical gating in one device with optimized alignment capabilities based on a
noncollinear geometry
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