Escherichia coli motion is characterized by a sequence of consecutive tumble-and-swim events. In the absence of chemical gradients, the length of individual swims is commonly believed to be distributed exponentially. However, recently there has been experimental indication that the swim-length distribution has the form of a power-law, suggesting that bacteria might perform superdiffusive Lévy-walk motion. In E. coli, the power-law behavior can be induced through stochastic fluctuations in the level of CheR, one of the key enzymes in the chemotaxis signal transmission pathway. We use a mathematical model of the chemotaxis signaling pathway to study the influence of these fluctuations on the E. coli behavior in the absence and presence of chemical gradients. We find that the population with fluctuating CheR performs Lévy-walks in the absence of chemoattractants, and therefore might have an advantage in environments where nutrients are sparse. The more efficient search strategy in sparse environments is accompanied by a generally larger motility, also in the presence of chemoattractants. The tradeoff of this strategy is a reduced precision in sensing and following gradients, as well as a slower adaptation to absolute chemoattractant levels.

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Various transition metal (TM) doped zinc oxide nanoparticles with the composition TM x Zn 1-x O (TM = V, Mn, Fe, Co, and Ni; x = 0.01-0.3) were prepared by a microwaveassisted nonaqueous sol-gel route in benzyl alcohol within a few minutes. The high doping levels in the range 20-30 atom % achieved for Co and Fe provide a promising opportunity to study the magnetic properties of such potential diluted magnetic semiconductors. However, only Fe 0.2 Zn 0.8 O was ferromagnetic at room temperature. The Co-doped sample showed Curie-Weiss behavior up to a doping level of 30 atom %. According to X-ray absorption fine structure (XAFS) measurements, at high doping levels the Fe-doped ZnO samples contain an increasing fraction of Fe 3þ ions (in addition to Fe 2þ ), whereas Co is predominantly in the oxidation state of þ2. Clustering of Fe ions into amorphous ferromagnetic Fe 3 O 4 within the ZnO host and the magnetic interactions between the Fe 3 O 4 regions is a possible explanation for the ferromagnetic properties.

We present a detailed study of 75 As nuclear magnetic resonance Knight shift and spin-lattice relaxation rate in the normal state of stoichiometric polycrystalline LiFeAs. Our analysis of the Korringa relation suggests that LiFeAs exhibits strong antiferromagnetic fluctuations, if transferred hyperfine coupling is a dominant interaction between 75 As nuclei and Fe electronic spins, whereas for an on-site hyperfine coupling scenario, these are weaker, but still present to account for our experimental observations. Density-functional calculations of electric field gradient correctly reproduce the experimental values for both 75 As and 7 Li sites.