Life-extending dietary restriction, but not dietary supplementation of branched-chain amino acids, can increase organismal oxidation rates of individual branched-chain amino acids by grasshoppers.

BACKGROUND: Life-extending dietary restriction increases energy demands. Branched-chain amino acids (BCAAs), at high levels, may be detrimental to healthspan by activating the mechanistic Target of Rapamycin (mTOR). Whether organismal oxidation of BCAAs increases upon dietary restriction is unknown. OBJECTIVE: Test whether dietary restriction (DR, which creates an energy deficit) or supplemental dietary BCAAs (superfluous BCAAs) increases oxidation of BCAAs, potentially reducing their levels to improve healthspan. METHODS: Grasshoppers were reared to middle-age on one of four diets, each a level of lettuce feeding and a force-fed solution: 1) ad libitum lettuce & buffer, 2) ad libitum lettuce & supplemental BCAAs, 3) DR lettuce & buffer, and 4) DR lettuce & supplemental BCAAs. On trial days, grasshoppers were force-fed one 13C-1-BCAA (isoleucine, leucine, or valine). Breath was collected and tested for 13CO2, which represents organismal oxidation of the amino acid. Additional trials re-tested oxidation of leucine (the most potent activator of mTOR) in both females and males on dietary restriction. RESULTS: Dietary restriction generally increased cumulative oxidation of each BCAA in females and hungry males over ∼8 hr. Results were consistent for isoleucine and valine, but less so for leucine. Supplementation of BCAAs, in combination with dietary restriction, increased isoleucine in hemolymph, with similar trends for leucine and valine. Despite this, supplementation of BCAAs did not alter oxidation of any BCAAs. CONCLUSIONS: Dietary restriction can increase oxidation of BCAAs, likely due to an energy deficit. The increased oxidation may decrease available BCAAs for activation of mTOR and improve healthspan.

Spatial correlation of solar-wind turbulence from two-point measurements.

Interplanetary turbulence, the best studied case of low frequency plasma turbulence, is the only directly quantified instance of astrophysical turbulence. Here, magnetic field correlation analysis, using for the first time only proper two-point, single time measurements, provides a key step in unraveling the space-time structure of interplanetary turbulence. Simultaneous magnetic field data from the Wind, ACE, and Cluster spacecraft are analyzed to determine the correlation (outer) scale, and the Taylor microscale near Earth's orbit.

Spectral distribution of the cross helicity in the solar wind.

There are a variety of theoretical and observational indications that fluctuation energy in astrophysical and space plasma turbulence is distributed anisotropically in space relative to the magnetic field direction. The cross helicity, represented by correlations between velocity and magnetic field fluctuations, enters a magnetohydrodynamic description on equal footing with the energy, but its anisotropy has not been examined in the same degree of detail. Here we employ Advanced Coronal Explorer data to examine the rotational symmetry of the cross helicity. We find that the normalized cross helicity is associated more or less equally with all angular components of the fluctuations. This favors turbulence models that allow for cross communication between parallel and perpendicular wave numbers, suggesting that "wavelike" and "turbulencelike" fluctuations are strongly coupled.

One-point statistics of the induced electric field in quasinormal magnetofluid turbulence.

We study one-point statistical properties of the induced turbulent electric field for a magnetohydrodynamic (MHD) plasma under the quasinormal approximation. Assuming exact Gaussianity for both the velocity field and the magnetic field, and different degrees of correlations between their Cartesian components, we derive the probability distribution function (PDF) for the Cartesian components of the electric field e(i). We show that the PDF reduces in some canonical cases to an exponential function of the form exp(-/e(i)/). To study deviations from these results in the more realistic case in which the velocity and magnetic fields are not exactly normal but quasinormal instead, we perform three-dimensional numerical simulations of the MHD equations at moderate Reynolds numbers. For turbulent relaxation from an initial condition, we find that the analytical results give a very good first-order approximation to the computed PDF.