Material Modelling of the Photopolymers for Additive Manufacturing Processes

Ultraviolet (UV) curing of polymers is a key phenomenon for several additive manufacturing technologies. This contribution presents a model relating the process parameters of UV light intensity and temperature to the thermal and mechanical properties of the polymer and the experimental results used to calibrate the model. Moreover, photo-differential scanning calorimetry (photo-DSC) measurements are performed to investigate the crosslinking reaction and to model the degree of cure as a function of the light intensity and temperature. The viscoelastic properties are measured by UV rheometry and it is shown that the classical time-cure superposition principle can equally be applied to the experimental results. Complete curing and mechanical model equations are provided to describe the material behavior as a result of our experimental findings.Mechanical Engineerin

Facing challenges in differential classical conditioning research: benefits of a hybrid design for simultaneous electrodermal and electroencephalographic recording

Several challenges make it difficult to simultaneously investigate central and autonomous nervous system correlates of conditioned stimulus (CS) processing in classical conditioning paradigms. Such challenges include, for example, the discrepant requirements of electroencephalography (EEG) and electrodermal activity (EDA) recordings with regard to multiple repetitions of conditions and sufficient trial duration. Here, we propose a MultiCS conditioning set-up, in which we increased the number of CSs, decreased the number of learning trials, and used trials of short and long durations for meeting requirements of simultaneous EEG–EDA recording in a differential aversive conditioning task. Forty-eight participants underwent MultiCS conditioning, in which four neutral faces (CS+) were paired four times each with aversive electric stimulation (unconditioned stimulus) during acquisition, while four different neutral faces (CS−) remained unpaired. When comparing after relative to before learning measurements, EEG revealed an enhanced centro-posterior positivity to CS+ vs. CS− during 368–600 ms, and subjective ratings indicated CS+ to be less pleasant and more arousing than CS−. Furthermore, changes in CS valence and arousal were strong enough to bias subjective ratings when faces of CS+/CS− identity were displayed with different emotional expression (happy, angry) in a post-experimental behavioral task. In contrast to a persistent neural and evaluative CS+/CS− differentiation that sustained multiple unreinforced CS presentations, electrodermal differentiation was rapidly extinguished. Current results suggest that MultiCS conditioning provides a promising paradigm for investigating pre–post-learning changes under minimal influences of extinction and overlearning of simple stimulus features. Our data also revealed methodological pitfalls, such as the possibility of occurring artifacts when combining different acquisition systems for central and peripheral psychophysiological measures

Biofisch – Qualitätsvergleich zwischen konventionellen und ökologisch produzierten Forellen

Die Studie umfasste die Untersuchung der Aufzuchtsbedingungen sowie Futterversuche und vergleichende Untersuchungen zur Produktqualität an Portionsforellen. Es wurden 2 ökologisch zertifizierte und 3 konventionelle Forellenzuchtbetriebe verglichen. In dieser Arbeit werden nur die Ergebnisse der Qualitätsuntersuchungen wiedergegeben. Die Untersuchungen der Portionsforellen beinhalteten die Erfassung der biologischen Parameter, die mikrobiologische und sensorische Beurteilung der Ware, Farb- und Texturmessungen, die Bestimmung der chemischen Zusammensetzung einschließlich der Rückstände sowie bildverarbeitende Methoden und die Aufnahme des Aromaprofils. Insgesamt waren die Qualität und der mikrobiologische Status aller untersuchten Forellen sehr gut. In ihrer chemischen Zusammensetzung unterschieden sich die Fische vor allem im Fettgehalt. Alle ermittelten Rückstandsgehalte lagen weit unter den zulässigen Höchstwerten. Unterschiede zwischen den Aufzuchtsformen wurden nicht gefunden

Qualitätsvergleich von Regenbogenforellen aus konventioneller und ökologisch zertifizierter Aufzucht als Voraussetzung für eine Verbesserung der Wettbewerbsfähigkeit von Bioforellen

Die Studie umfasste die Untersuchung der Aufzuchtsbedingungen sowie Futterversuche und vergleichende Untersuchungen zur Produktqualität. Es wurden 2 ökologisch zertifizierte und 3 konventionelle Forellenzuchtbetriebe verglichen. Tagesgänge verschiedener wasserchemischer Parameter an Zu- und Ablauf der Teiche umfassten die Bestimmung von Temperatur, Sauerstoff, pH-Wert, Ammonium-, Nitrit-, Gesamt- und ortho-Phosphatgehalt sowie CSB- und Feststoffgehalt. In zwei Futterversuchen wurden Ökofutter für Forellen mit konventionellen Futtern hinsichtlich Wachstum, Futterverwertung und Proteinausnutzung verglichen. Die zwei untersuchten ökologischen Futtermittel zeigten im Vergleich ein schlechteres Protein-/Energieverhältnis, das sich in niedrigeren Rohfettgehalten ausdrückte. Zusätzlich wurden futterbedingte Stickstoffexkretionsmuster von Forellen im Tagesgang untersucht. Im Ergebnis zeigte sich, dass die Ökofutter im Vergleich zu den konventionellen Futtern zu einer stärkeren Umweltbelastung und einem geringerem Wachstum bei schlechterer Futterverwertung führten. Die Qualitätsuntersuchungen der Forellen beinhalteten die Erfassung der biologischen Para-meter, die mikrobiologische und sensorische Beurteilung der Ware, Farb- und Texturmessun-gen, die Bestimmung der chemischen Zusammensetzung einschließlich der Rückstände sowie bildverarbeitende Methoden und die Aufnahme des Aromaprofils. Insgesamt waren die Produktqualität und der mikrobiologische Status aller untersuchten Forellen sehr gut. In ihrer chemischen Zusammensetzung unterschieden sich die Fische vor allem im Fettgehalt. Alle ermittelten Rückstandsgehalte lagen weit unter den zulässigen Höchstwerten. Ein Zusammenhang zwischen der Aufzuchtsform und der Qualität konnte nicht festgestellt werden. Bei den Projektergebnissen handelt es sich um eine Abschätzung der Situation ausgewählter Forellenzuchtbetriebe, repräsentative Aussagen können aus den Ergebnissen nicht abgeleitet werden

Tensile Overload and Stress Intensity Shielding Investigations by Ultrasound

Growth of a fatigue crack is modified according to the development of contacts between the crack faces [1,2] creating shielding, thus canceling a portion of the crack driving force. These contacts develop through a number of mechanisms, including plastic deformation, sliding of the faces with respect to each other and the collection of debris such as oxide particles [3]. Compressive stresses are created on either side of the partially contacting crack faces resulting in opening loads that must be overcome in order to apply a driving force at the crack tip. In this way, the crack tip is shielded from a portion of the applied load, thus creating the need for modification [1] of the applied stress intensity range from ΔK = KImax − KImin to ΔKeff = KImax − KIsh. Determination of the contact size and density in the region of closure from ultrasonic transmission and diffraction experiments [4] has allowed estimation of the magnitude of Kish on a crack grown under constant ΔK conditions. The calculation has since [5] been extended to fatigue cracks grown with a tensile overload block. The calculation was also successful in predicting the growth rate of the crack after reinitiation had occurred. This paper reports the further extension to the effects of a variable ΔK on fatigue crack growth. In addition, this paper presents preliminary results on detection of the tightly closed crack extension present during the growth retardation period after application of a tensile overload as well as an observation of the crack surface during reinitiation of growth that presents some interesting questions

Facing challenges in differential classical conditioning research: benefits of a hybrid design for simultaneous electrodermal and electroencephalographic recording

Several challenges make it difficult to simultaneously investigate central and autonomous nervous system correlates of conditioned stimulus (CS) processing in classical conditioning paradigms. Such challenges include, for example, the discrepant requirements of electroencephalography (EEG) and electrodermal activity (EDA) recordings with regard to multiple repetitions of conditions and sufficient trial duration. Here, we propose a MultiCS conditioning set-up, in which we increased the number of CSs, decreased the number of learning trials, and used trials of short and long durations for meeting requirements of simultaneous EEG–EDA recording in a differential aversive conditioning task. Forty-eight participants underwent MultiCS conditioning, in which four neutral faces (CS+) were paired four times each with aversive electric stimulation (unconditioned stimulus) during acquisition, while four different neutral faces (CS−) remained unpaired. When comparing after relative to before learning measurements, EEG revealed an enhanced centro-posterior positivity to CS+ vs. CS− during 368–600 ms, and subjective ratings indicated CS+ to be less pleasant and more arousing than CS−. Furthermore, changes in CS valence and arousal were strong enough to bias subjective ratings when faces of CS+/CS− identity were displayed with different emotional expression (happy, angry) in a post-experimental behavioral task. In contrast to a persistent neural and evaluative CS+/CS− differentiation that sustained multiple unreinforced CS presentations, electrodermal differentiation was rapidly extinguished. Current results suggest that MultiCS conditioning provides a promising paradigm for investigating pre–post-learning changes under minimal influences of extinction and overlearning of simple stimulus features. Our data also revealed methodological pitfalls, such as the possibility of occurring artifacts when combining different acquisition systems for central and peripheral psychophysiological measures