A convolutional neural network approach to calibrating the rotation axis for X‐ray computed tomography

This paper presents an algorithm to calibrate the center‐of‐rotation for X‐ray tomography by using a machine learning approach, the Convolutional Neural Network (CNN). The algorithm shows excellent accuracy from the evaluation of synthetic data with various noise ratios. It is further validated with experimental data of four different shale samples measured at the Advanced Photon Source and at the Swiss Light Source. The results are as good as those determined by visual inspection and show better robustness than conventional methods. CNN has also great potential for reducing or removing other artifacts caused by instrument instability, detector non‐linearity, etc. An open‐source toolbox, which integrates the CNN methods described in this paper, is freely available through GitHub at tomography/xlearn and can be easily integrated into existing computational pipelines available at various synchrotron facilities. Source code, documentation and information on how to contribute are also provided.     

Liquid-liquid phase separation of a surfactant-solubilized membrane protein

Solubilization of membrane proteins requires surfactants, whose structural properties play a crucial role in determining the protein phase behavior. We show that ionization of a pH-sensitive surfactant, lauryldymethylamino-N-oxide, bound to the bacterial photosynthetic Reaction Center, induces protein phase segregation in micrometric "droplets." Liquid-liquid phase separation takes place in a narrow pH range, is promoted by increasing temperature, and vanishes by adding salt. After a fast initial droplet growth, the nearly arrested kinetics at a later stage leaves the system in a finely divided, long-lasting emulsified state.     

Solvent effects on charge spatial extent in DNA and implications for transfer

To clarify the role played by water in facilitating long-range DNA charge transport, carefully designed, state-of-the-art, self-interaction corrected density-functional quantum mechanical and molecular mechanical (SIC-QM/MM) simulations are performed for the first time on two ionized adenine:thymine bridge models in explicit water solvent at finite temperature. For random solvent configurations, the charge is partially delocalized. However, a charge localization on different, well-separated adenines can be induced and is correlated with a restructuring of their first solvation shells. Thus, the importance of water in the mechanism of long-range charge transport is explicitly demonstrated, and the microscopic conditions for a charge localization are revealed.     

Playing with Numbers, with Fermions and Bosons

We construct nonlinear maps which realize the fermionization of bosons and the bosonization of fermions with the view of obtaining states coding naturally integers in standard or in binary basis. Specifically, with reference to spin systems, we derive raising and lowering bosonic operators in terms of standard fermionic operators and vice versa. The crucial role of multiboson operators in the whole construction is emphasized. Dedicated to Giuseppe Castagnoli for his 65th birthday.     

High-Frequency Gravitational Waves in Electromagnetic Waveguides

The interaction between a very-high-frequency gravitational wave (VHFGW) and an electromagnetic wave (EMW) in a rectangular waveguide is discussed in the weak field limit. The background EMW is assumed to be initially in the TE₁₀ mode along the waveguide. It is then shown that a VHFGW, having the same frequency and direction of propagation of the EMW, induces through the waveguide a TE mode with a frequency doubled when compared to the original EMW frequency. In that respect, the GW acts similar to a non-linear medium, giving rise to a Second Harmonic Generation (SHG) effect.     

Studies of R.F. discharges at moderate pressures and chemical applications—II. Nitrogen-hydrogen,nitrogen-methane and nitrogen-methane-hydrogen mixtures

Simultaneous vibro-rotational analyses have been carried out for the second positive system (SPS) of N₂ (C³П_u ? B³П_g), for the violet system (VS) of CN (B²Σ ? X²Σ) and for the Swan system (SS) of C₂ (d³П_g ? a³П_u), emitted by 35 MHz electrical discharges, containing N₂, H₂ and CH₄ flowing mixture s, in the 5–40 torr pressure range and at 1–10 Wcm^-3 power densities. The results are consistent with a Boltzman distribution for the rotational levels, but they show a deviation from this law for upper vibrational levels of CN and C₂.