Dynamic Phase Alignment in Inertial Alfvén Turbulence.

In weakly collisional plasma environments with sufficiently low electron beta, Alfvénic turbulence transforms into inertial Alfvénic turbulence at scales below the electron skin depth, k_{⊥}d_{e}≳1. We argue that, in inertial Alfvénic turbulence, both energy and generalized kinetic helicity exhibit direct cascades. We demonstrate that the two cascades are compatible due to the existence of a strong scale dependence of the phase alignment angle between velocity and magnetic field fluctuations, with the phase alignment angle scaling as cosα_{k}∝k_{⊥}^{-1}. The kinetic and magnetic energy spectra scale as ∝k_{⊥}^{-5/3} and ∝k_{⊥}^{-11/3}, respectively. As a result of the dual direct cascade, the generalized helicity spectrum scales as ∝k_{⊥}^{-5/3}, implying progressive balancing of the turbulence as the cascade proceeds to smaller scales in the k_{⊥}d_{e}≫1 range. Turbulent eddies exhibit a phase-space anisotropy k_{∥}∝k_{⊥}^{5/3}, consistent with critically balanced inertial Alfvén fluctuations. Our results may be applicable to a variety of geophysical, space, and astrophysical environments, including the Earth's magnetosheath and ionosphere, solar corona, and nonrelativistic pair plasmas, as well as to strongly rotating nonionized fluids.

Rational selection of biphasic reaction systems for geranyl glucoside production by Escherichia coli whole-cell biocatalysts.

Geranyl glucoside, the glucosylated, high-value derivative of the monoterpenoid geraniol, has various applications in the flavor and fragrance industry and can be produced through whole-cell biotransformation of geraniol with Escherichia coli whole-cell biocatalysts expressing the glucosyltransferase VvGT14a. However, the low water solubility and high cytotoxicity of geraniol require the design of a proper biphasic system where the second, non-aqueous phase functions as an in-situ substrate reservoir. In this work, a rational selection strategy was applied for choosing suitable sequestering phases for geranyl glucoside production by whole-cell biotransformation of geraniol. Hansen solubility parameters and octanol/water distribution coefficients were used as first principle methods in combination with extensive database research to preselect 12 liquid and 6 solid sequestering phases. Subsequently, experimental approaches were applied to determine physicochemical characteristics and the distribution of geraniol and geranyl glucoside between the phases. Moreover, the effects of the sequestering phases on the whole-cell biocatalysts and on the produced geranyl glucoside concentration were measured during parallel biotransformations in milliliter-scale stirred-tank bioreactors. The fatty acid ester isopropyl myristate emerged as the best choice due to its low viscosity, very poor water solubility, low price and compatibility with the whole-cell biocatalyst. The biphasic system containing 20% (v/v) of this solvent boosted geranyl glucoside production (4.2-fold increase of geranyl glucoside concentration in comparison to aqueous system) and exhibits advantageous partitioning of geraniol into the organic phase (logD of 2.42±0.03) and of geranyl glucoside into the water phase (logD of -2.08±0.05). The systematic selection of a suitable biphasic system constitutes basic groundwork for the development of new bioprocesses involving geraniol. Moreover, this study can serve as a guideline for selecting sequestering phases for other whole-cell biotransformation processes.