Enhancing the Thermal Stability of Polyamide 6 in Powder Bed Fusion via Primary and Secondary Antioxidant Incorporation

Polyamide 6 (PA6) is a thermoplastic material widely used in manufacturing for its excellent mechanical properties, such as high strength, stiffness, and toughness. However, its suitability for powder bed fusion (PBF) is limited due to its susceptibility to thermo-oxidative aging, resulting in material degradation and mechanical property deterioration over time. To address this issue, the efficacy of antioxidants in increasing the aging resistance of PA6 in PBF was investigated. Process-adapted analysis was employed using a coupled rheometer FTIR instrument to elucidate physical and chemical changes in the material. In addition, the viscosity number of the virgin and processed powder, the yellow index, and the part performance were evaluated. Results revealed that the addition of primary and secondary antioxidants significantly enhanced the aging resistance of PA6 in PBF, thereby increasing its potential as a suitable material for additive manufacturing applications.Mechanical Engineerin

Analysis of Flow Additives in Laser-Based Powder Bed Fusion of Polymers: Implications for Flow Behavior, Processing, Temperature Profile, and Part Characteristics

Powder bed fusion of polymers requires the use of flow additives to ensure adequate flowability of the feedstock material. However, information regarding flow additives and their load is limited, as is an understanding of their impact on processing conditions. This study investigates the flow behavior using static and dynamic measurements under process conditions, focusing on the influence of flow additives. Subsequently, processing studies are conducted using thermography to analyze the laser-material interaction. The characteristics of parts produced from Polypropylene and Polyamide 12 systems are also examined. The findings of this research enhance the understanding of the impact of flow additives on the processing conditions of laser-based powder bed fusion of polymers, potentially leading to optimized process parameters and improved part quality and mechanical properties.Mechanical Engineerin

Exploring phase coherence in a 2D lattice of Bose-Einstein condensates

Bose-Einstein condensates of rubidium atoms are stored in a two-dimensional periodic dipole force potential, formed by a pair of standing wave laser fields. The resulting potential consists of a lattice of tightly confining tubes, each filled with a 1D quantum gas. Tunnel-coupling between neighboring tubes is controlled by the intensity of the laser fields. By observing the interference pattern of atoms released from more than 3000 individual lattice tubes the phase coherence of the coupled quantum gases is studied. The lifetime of the condensate in the lattice and the dependence of the interference pattern on the lattice configuration are investigated.Comment: 4 pages, 6 figure

Decoherence of Bose-Einstein condensates in traps at finite temperature

The phase diffusion of the order parameter of trapped Bose-Einstein condensates at temperatures large compared to the mean trap frequency is determined, which gives the fundamental limit of the line-width of an atom laser. In addition a prediction of the correlation time of the number fluctuations in the condensate is made and related to the phase diffusion via the fluctuation-dissipation relation.Comment: 4 pages Revtex, revised version, to appear in Phys. Rev. Letter

Spastische Parese der Arme und schlaffe Plegie der Beine bei sekundär-progredienter Multipler Sklerose

Substanzinduzierte psychotische Störungen (SIPS) sind häufig und für ca. 25 % der ersten Einweisungen in eine psychiatrische Klinik verantwortlich. Aus klinischer Sicht ist aufgrund ähnlicher psychopathologischer Phänomene die diagnostische Unterscheidung zwischen SIPS und primären (genuinen oder kryptogenen) psychotischen Störungen oft eine Herausforderung. Dieser Umstand wird dadurch erschwert, dass SIPS im Zusammenhang mit Cannabis, Halluzinogenen und Amphetaminen ein erhebliches Risiko des Übergangs in eine primäre psychotische Störung (z. B. Schizophrenie) haben. Im ersten Abschnitt dieser Arbeit werden zunächst zwei exemplarische Fallvignetten aus der allgemeinpsychiatrischen und forensischen Praxis vorgestellt. Danach wird im Sinne einer selektiven Literaturübersicht die Relevanz der differenzialdiagnostischen Unterscheidung beider Störungsbilder aus der Sicht der allgemeinen und forensischen Psychiatrie in Bezug auf Therapie, Prognose und richterliche Entscheidung bezüglich der Unterbringung im Maßregelvollzug (§ 63 vs. § 64 StGB) beleuchtet. Der letzte Abschnitt hat das Ziel, ein strukturiertes Vorgehen zur differenzialdiagnostischen Unterscheidung zwischen SIPS und primären psychotischen Störungen zu erarbeiten. Die in dieser Arbeit dargestellten und diskutierten Konzepte und Befunde sollen klinisch tätigen Psychiatern und Psychologen die Diagnosestellung im allgemeinen und forensischen Kontext erleichtern