Influence of arsenic on the corrosion resistance of low-carbon low-alloy steel. Part 1

Literature data regarding the influence of arsenic on the corrosion resistance of low-carbon low-alloy steel are analyzed. A mechanism explaining this influence in air and in sea water is proposed.     

pH-Dependent Protonation of Surface Carboxylate Groups in PsbO Enables Local Buffering and Triggers Structural Changes

Photosystem II (PSII) catalyzes the splitting of water, releasing protons and dioxygen. Its highly conserved subunit PsbO extends from the oxygen-evolving center (OEC) into the thylakoid lumen and stabilizes the catalytic Mn₄CaO₅ cluster. The high degree of conservation of accessible negatively charged surface residues in PsbO suggests additional functions, as local pH buffer or by affecting the flow of protons. For this discussion, we provide an experimental basis, through the determination of pK_a values of water-accessible aspartate and glutamate side-chain carboxylate groups by means of NMR. Their distribution is strikingly uneven, with high pK_a values around 4.9 clustered on the luminal PsbO side and values below 3.5 on the side facing PSII. pH-dependent changes in backbone chemical shifts in the area of the lumen-exposed loops are observed, indicating conformational changes. In conclusion, we present a site-specific analysis of carboxylate group proton affinities in PsbO, providing a basis for further understanding of proton transport in photosynthesis.     

Correction to: Hydrodynamic Tests of Small-Sized Circulating Water Cooling Devices

Chemical and Petroleum Engineering - To the article “Hydrodynamic Tests of Small-Sized Circulating Water Cooling Devices,” by K. E. Bondar’, N. S. Shulaev, and S. P. Ivanov, Vol....     

The Cr ― Ta ― C Melting Diagram in the (Cr) ― (Ta) ― (TaC) Region

It has been found from an experimental study on alloys in the Cr Ta C system in the region of the (Cr) (Ta) (TaC) subsystem at melting (crystallization) temperatures that there are two nonvariant four-phase equilibria of congruent type: L_E (Ta) + (Ta₂C) + (TaCr₂) at 1935°C and L_E (TaC) + (Cr) + (TaCr₂) at 1675°C; there is also one four-phase nonvariant equilibrium of incongruent transition type: L_U + (Ta₂C) (TaC) + (TaCr₂) at 1943°C, and two nonvariant three-phase equilibria of congruent type: L_e (Ta₂C) + (TaCr₂) at 1960°C and L_e (TaC) + (Cr) at 1695°C. The phase diagram for the subsystem has been constructed in the form of projections of the solidus and liquidus surfaces, and a melting diagram has been constructed.     

The inverse problem of the phenomenological theory of the optical properties of thin films

For thin metal films the solution of the inverse problem of the phenomenological theory of the optical properties of thin films is incorrect when the ratio of the film thickness to the incident light wavelength becomes less than 0.05 because the set of equations describing the relation between the measured optical characteristics and the optical constants of the film is virtually a set of linear equations with determinant equal to zero. For this reason the usual methods of solving the inverse problem give ambiguous solutions (optical constants) which are unstable to small errors in the measured optical characteristics. If the method of continuous differential descent is used as the regularization method for solution of this inverse problem unambiguous and stable solutions can be obtained.     

Nonlinear transmission and excited-state absorption in fluorene derivatives

The nonlinear transmission and the excited-state absorption spectra of three fluorene derivatives exhibiting large two-photon absorptivity were measured by the third harmonic of a picosecond Nd:YAG laser. We analyzed their capability for exhibiting stimulated emission in polar solvents and found that asymmetrical fluorene compounds with a diphenylamino substituent exhibited large Stokes shifts (approximately 8000 cm(-1)), high quantum yields (approximately 0.9-1.0), and no optical gain over their entire fluorescence spectral region. In contrast, a symmetrical fluorene derivative with vinylphenylbenzothiazole substituents in positions 2 and 7 underwent lasing under one-photon excitation by use of picosecond pulsed irradiation.     

A sample and hold device

Typical sample and hold devices (SHDs) are characterized by a number of drawbacks: zero offset at the SHD output caused mainly by the zero-offset voltage of the operational amplifiers that are parts of the SHD, significant sampling time due to the need to use a storage capacitor with the largest possible capacity to increase the storage time, and the uncertainty of the sampling time conditioned by the recharge mode of the storage capacitor, which is a commutation process with nonzero initial conditions of a random character. An attempt to stabilize the sampling time with simultaneous minimization resulted in the development of an accelerated recharging procedure for the SHD storage capacitor based on amplification of the input signal, forced recharging of the storage capacitor, and determination of the amplitude equity moment of the memorized analogue system and the SHD output signal.     

Structure of B-Mo-Nb Alloys and Phase Equilibria in the Range of Melting-Solidification

B-Mo-Nb alloys, as-cast and annealed at subsolidus temperatures, were experimentally studied by x-ray diffraction technique and scanning electron microscopy with electron probe microanalyses. Temperatures of incipient melting were measured by pyrometry after Pirani and Alterthum. No ternary compound was found in the examined alloys. Based on the experimental data, the B-Mo-Nb phase diagram was constructed for the first time, including liquidus and solidus surface projections and Scheil’s reaction scheme.