Continuous and discontinuous quantum phase transitions in a model two-dimensional magnet

The Shasty-Sutherland model, which consists of a set of spin 1/2 dimers on a 2D square lattice, is simple and soluble but captures a central theme of condensed matter physics by sitting precariously on the quantum edge between isolated, gapped excitations and collective, ordered ground states. We compress the model Shastry-Sutherland material, SrCu(2)(BO(3))(2), in a diamond anvil cell at cryogenic temperatures to continuously tune the coupling energies and induce changes in state. High-resolution X-ray measurements exploit what emerges as a remarkably strong spin-lattice coupling to both monitor the magnetic behavior and the absence or presence of structural discontinuities. In the low-pressure spin-singlet regime, the onset of magnetism results in an expansion of the lattice with decreasing temperature, which permits a determination of the pressure-dependent energy gap and the almost isotropic spin-lattice coupling energies. The singlet-triplet gap energy is suppressed continuously with increasing pressure, vanishing completely by 2 GPa. This continuous quantum phase transition is followed by a structural distortion at higher pressure.     

Factors Affecting Survival and Usefulness of Implants Placed in Vascularized Free Composite Grafts Used in Post–Head and Neck Cancer Reconstruction

Background: Bone‐containing vascularized grafts have been used successfully to reconstruct post‐cancer surgical defects. Dental implants can be placed in these bone‐containing grafts to allow implant‐supported prosthodontic reconstruction of these patients. Purpose: The aim of this study was to evaluate the survival of dental implants used in the rehabilitation of subjects treated with bone‐containing vascularized grafts to compare usability of implants placed at the time of reconstruction and after healing. Materials and Methods: A cross‐sectional study was undertaken to examine survival rates of implants placed in vascularized bone‐containing grafts either immediately at the time of surgical reconstruction or after 3 months healing. Other factors such as graft type, whether radiation therapy was given, and implant type were recorded. Results: A total of 41 patients had 145 implants placed in 47 vascularized bone‐containing flaps. Increased failure rate of implants was seen in immediately placed implants. There was also a significant increase in the number of osseointegrated implants that were prosthodontically unusable or sub‐optimally placed in the immediate placement group. Radiation therapy was associated with a significant increase in failure rate. Modern implant surfaces appeared to perform better than machined/turned surfaces. Graft donor site did not influence implant survival. Conclusion: This study demonstrated the difficulties encountered with immediate placement of dental implants at the time of post‐cancer reconstructive surgery.