Self-trapping of magnon Bose-Einstein condensates in the ground state and on excited levels: from harmonic to box confinement.

Long-lived coherent spin precession of (3)He-B at low temperatures around 0.2T(c) is a manifestation of Bose-Einstein condensation of spin-wave excitations or magnons in a magnetic trap which is formed by the order-parameter texture and can be manipulated experimentally. When the number of magnons increases, the orbital texture reorients under the influence of the spin-orbit interaction and the profile of the trap gradually changes from harmonic to a square well, with walls almost impenetrable to magnons. This is the first experimental example of Bose condensation in a box. By selective rf pumping the trap can be populated with a ground-state condensate or one at any of the excited energy levels. In the latter case the ground state is simultaneously populated by relaxation from the exited level, forming a system of two coexisting condensates.

Direct write assembly of calcium phosphate scaffolds using a water-based hydrogel.

The development of materials to support bone regeneration requires flexible fabrication technologies able to tailor chemistry and architecture for specific applications. In this work we describe the preparation of ceramic-based inks for robotic-assisted deposition (robocasting) using Pluronic F-127 solutions. This approach allows the preparation of pseudoplastic inks with solid contents ranging between 30 and 50 vol.%, enabling them to flow through a narrow printing nozzle while supporting the weight of the printed structure. Ink formulation does not require manipulation of the pH or the use of highly volatile organic components. Therefore, the approach can be used to prepare materials with a wide range of compositions, and here we use it to build hydroxyapatite (HA), beta-tricalcium phosphate (beta-TCP) and biphasic (HA/beta-TCP) structures. The flow of the inks is controlled by the Pluronic content and the particle size distribution of the ceramic powders. The use of wide size distributions favors flow through the narrow printing nozzles and we have been able to use printing nozzles as narrow as 100 microm in diameter, applying relatively low printing pressures. The microporosity of the printed lines increases with increasing Pluronic content and lower sintering temperatures. Microporosity can play a key role in determining the biological response to the materials, but it also affects the strength of the structure.