On the valence bond solid in the presence of Dzyaloshinskii-Moriya interaction

We examine the stability of the valence bond solid (VBS) phase against the Dzyaloshinskii-Moriya (DM) interaction in the bipartite lattice. Despite the VBS is vulnerable against the antiferromagnetic interaction, for example in the Q-J model proposed by Sandvik, where the quantum phase transition occurs at $J^*/Q = 0.04$, we found that on the contrary the VBS is very stable against the DM interaction. The quantum phase transition does not occur until D/Q goes to infinity, where D is the strength of the DM interaction. The VBS in the ALKT model and the Haldane gap system also exhibit the same property.Comment: 5 pages and 5 figure

Testing the phenomenological interacting dark energy with observational H(z)H(z) data

In order to test the possible interaction between dark energy and dark matter, we investigate observational constraints on a phenomenological scenario, in which the ratio between the dark energy and matter densities is proportional to the power law case of the scale factor, $r\equiv (\rho_X/\rho_m)\propto a^{\xi}$. By using the Markov chain Monte Carlo method, we constrain the phenomenological interacting dark energy model with the newly revised $H(z)$ data, as well as the cosmic microwave background (CMB) observation from the 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) results, the baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey (SDSS) data release 7 (DR7) galaxy sample and the type Ia supernovae (SNe Ia) from Union2 set. The best-fit values of the model parameters are $\Omega_{m0}=0.27_{-0.02}^{+0.02}(1\sigma)_{-0.03}^{+0.04}(2\sigma)$, $\xi=3.15_{-0.50}^{+0.48}(1\sigma)_{-0.71}^{+0.72}(2\sigma)$, and $w_X=-1.05_{-0.14}^{+0.15}(1\sigma)_{-0.21}^{+0.21}(2\sigma)$, which are more stringent than previous results. These results show that the standard $\Lambda$CDM model without any interaction remains a good fit to the recent observational data; however, the interaction that the energy transferring from dark matter to dark energy is slightly favored over the interaction from dark energy to dark matter. It is also shown that the $H(z)$ data can give more stringent constraints on the phenomenological interacting scenario when combined to CMB and BAO observations, and the confidence regions of $H(z)$+BAO+CMB, SNe+BAO+CMB, and $H(z)$+SNe+BAO+CMB combinations are consistent with each other.Comment: 6 pages, 4 figures, 1 table. MNRAS in pres

2,3-butanediol production from cellobiose by engineered Saccharomyces cerevisiae

Production of renewable chemicals from cellulosic biomass is a critical step towards energy sustainability and reduced greenhouse gas emissions. Microbial cells have been engineered for producing fuels and chemicals from cellulosic sugars. Among these chemicals, 2,3-butanediol (2,3-BDO) is a compound of interest due to its diverse applications. While microbial production of 2,3-BDO with high yields and productivities has been reported, there are concerns with the use of potential pathogenic bacteria and inefficient utilization of cellulosic sugars. To address these problems, we engineered Saccharomyces cerevisiae to produce 2,3-BDO, especially from cellobiose which is a prevalent sugar in cellulosic hydrolyzates. Specifically, we overexpressed alsS and alsD from Bacillus subtilis to convert pyruvate to 2,3-BDO via α-acetolactate and acetoin in engineered S. cerevisiae capable of fermenting cellobiose directly. Under oxygen-limited conditions, the resulting strain was able to produce 2,3-BDO. Still, the majority of carbon flux in the strain went to ethanol, resulting in significant amounts of ethanol production. To enhance pyruvate flux to 2,3-BDO through elimination of the pyruvate decarboxylation (PDC) reaction, we employed a deletion mutant of both PDC1 and PDC5 for producing 2,3-BDO from cellobiose. The subsequent strain was able to produce only 2,3-BDO without ethanol production from cellobiose under oxygen-limited conditions. These results suggest the possibility of producing 2,3-BDO safely and sustainably from cellulosic hydrolyzates