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The possibility of constructing a complete, continuous Wigner function for any quantum system has been a subject of investigation for over 50 years. A key system that has served to illustrate the difficulties of this problem has been an ensemble of spins. Here we present a general and consistent framework for constructing Wigner functions exploiting the underlying symmetries in the physical system at hand. The Wigner function can be used to fully describe any quantum system of arbitrary dimension or ensemble size.

We study a lattice bipolaron on a staggered triangular ladder and triangular and hexagonal lattices with both long-range electron-phonon interaction and strong Coulomb repulsion using a novel continuous-time quantum Monte Carlo algorithm to solve the two-particle Coulomb-Fröhlich model. The algorithm is preceded by an exact integration over phonon degrees of freedom, and as such is extremely efficient. The bipolaron effective mass and radius are computed. Bipolarons on lattices constructed from triangular plaquettes have a novel crablike motion, and are small but very light over a wide range of parameters. We discuss the conditions under which such particles may form a Bose-Einstein condensate with high transition temperature, proposing a route to room temperature superconductivity.

Thermodynamic properties of one-dimensional lattice models exhibiting entropy-driven phase transformations are discussed in quantum and classical regimes. Motivated by the multistability of compounds exhibiting photoinduced phase transitions, we consider systems with asymmetric, double, and triple well on-site potential. One finds that among a variety of regimes, quantum versus classical, discrete versus continuum, a key feature is asymmetry distinguished as a "shift" type and "shape" type in limiting cases. The behavior of the specific heat indicates one phase transformation in a "shift" type and a sequence of two phase transformations in "shape"-type systems. Future analysis in higher dimensions should allow us to identify which of these entropy-driven phase transformations would evolve into phase transitions of the first order.

Objective: To measure the excretion of bupropion and its metabolites in breast milk. A secondary objective was to determine whether the drug accumulated in the nursing infant., Case Summary: Milk and plasma samples were collected from a woman taking bupropion 300 mg/d in divided doses who was breastfeeding her 14-month-old son. A single plasma sample was collected from the infant., Results: After a 100-mg dose, the peak bupropion breast milk concentration measured at two hours was 0.189 micrograms/mL. Milk-to-plasma ratios ranged from 2.51 to 8.58 over a six-hour interval. Two of three metabolites also were measured in milk. Bupropion and its metabolites were not detected in the single plasma sample obtained from the infant., Conclusions: Bupropion accumulates in human breast milk in concentrations much higher than in maternal plasma. Two metabolites are also excreted into the milk. Neither bupropion nor its metabolites were detected in the infant's plasma, indicating that accumulation did not occur in this infant.