We determine the thermodynamic properties and the spectral function for a homogeneous twodimensional Fermi gas in the normal state using the Luttinger-Ward, or self-consistent T-matrix, approach. The density equation of state deviates strongly from that of the ideal Fermi gas even for moderate interactions, and our calculations suggest that temperature has a pronounced effect on the pressure in the crossover from weak to strong coupling, consistent with recent experiments. We also compute the superfluid transition temperature for a finite system in the crossover region. There is a pronounced pseudogap regime above the transition temperature: the spectral function shows a Bogoliubov-like dispersion with back-bending, and the density of states is significantly suppressed near the chemical potential. The contact density at low temperatures increases with interaction and compares well with both experiment and zero-temperature Monte Carlo results.The formation of fermion pairs and superfluidity of such pairs are distinct but related phenomena: in weakcoupling BCS theory, both are predicted to occur at the same temperature T c . However, a basic question of many-body physics is how they are related at stronger coupling and in low dimensions, where quantum fluctuations play a large role. While preformed pairs in the normal phase trivially exist in the strong-coupling Bose limit where one has tightly bound dimers, it has been argued that pairing above T c can also occur in the BCS regime. In this case, one expects a significant suppression of spectral weight at the Fermi surface even above T c . This socalled pseudogap regime extends up to a crossover temperature T * > T c , and its spectral and thermodynamic properties deviate strongly from the predictions of Fermiliquid theory [1]. Recently, pairing and superfluidity have been studied in ultracold atomic gases, which afford accurate control of both the interaction strength and dimensionality, and allow access to the crossover between the BCS and Bose regimes [2]. In these systems, a pseudogap can be detected through the suppression of the spin susceptibility or directly via the spectral function, which is experimentally accessible by ARPES or momentumresolved rf spectroscopy [3,4]. The possibility of a pseudogap regime has already been investigated both experimentally and theoretically in three dimensions (3D) [3,5].In two-dimensional (2D) Fermi gases, the pseudogap regime is expected to be much more pronounced than in 3D, and a pairing gap has recently been observed experimentally [4]. Here, we compute the spectral function for the homogeneous 2D Fermi gas in the normal phase of the BCS-Bose crossover. We indeed find a strong suppression of the density of states at the Fermi surface above T c , as shown in Fig. 1. This allows us to map the extent of the pseudogap regime in the temperature-vs-coupling phase diagram (Fig. 4), and we find that it extends further than in 3D [6].As the binding between fermions increases, the Cooper pairs evolve into a Bose gas of tightly ...

A variety of methods (in total seven) comprising different combinations of internal and Cartesian coordinates are tested for interpolation and alignment in connection attempts for polypeptide rearrangements. We consider Cartesian coordinates, the internal coordinates used in CHARMM, and natural internal coordinates, each of which has been interfaced to the OPTIM code and compared with the corresponding results for united-atom force fields. We show that aligning the methylene hydrogens to preserve the sign of a local dihedral angle, rather than minimizing a distance metric, provides significant improvements with respect to connection times and failures. We also demonstrate the superiority of natural coordinate methods in conjunction with internal alignment. Checking the potential energy of the interpolated structures can act as a criterion for the choice of the interpolation coordinate system, which reduces failures and connection times significantly.

Multiple scales in metapopulations can give rise to paradoxical behavior: in a conceptual model for a public goods game, the species associated with a fitness cost due to the public good production can be stabilized in the well-mixed limit due to the mere existence of these scales. The scales in this model involve a length scale corresponding to separate patches, coupled by mobility, and separate time scales for reproduction and interaction with a local environment. Contrary to the well-mixed high mobility limit, we find that for low mobilities, the interaction rate progressively stabilizes this species due to stochastic effects, and that the formation of spatial patterns is not crucial for this stabilization.

We consider dipolar bosons in two tubes of one-dimensional lattices, where the dipoles are aligned to be maximally repulsive and the particle filling fraction is the same in each tube. In the classical limit of zero intersite hopping, the particles arrange themselves into an ordered crystal for any rational filling fraction, forming a complete devil's staircase like in the single tube case. Turning on hopping within each tube then gives rise to a competition between the crystalline Mott phases and a liquid of defects or solitons. However, for the two-tube case, we find that solitons from different tubes can bind into pairs for certain topologies of the filling fraction. This provides an intriguing example of pairing that is purely driven by correlations close to a Mott insulator.