The effect of hydration of ions of inorganic salts on the shape of the Raman stretching band of water

The shape of the Raman stretching band of water molecules in aqueous solutions of electrolytes KBr, KCl, KI, NaCl, and NaI is studied. It is confirmed that the characteristics of the stretching band strongly depend on the concentration and type of salt. The behavior of different parameters of the band is explained in terms of the theory of hydration of salts.     

Visible photoluminescence from silicon nanopowders produced by silicon evaporation in a high-power electron beam

Silicon nanopowders produced by electron-beam-induced evaporation of a bulk silicon sample in an argon atmosphere are studied by the photoluminescence technique and Raman scattering spectroscopy. A photoluminescence peak in the visible region of the spectrum has been detected at room temperature in powders consisting of silicon nanocrystals. The strong short-wavelength shift of the photoluminescence peak can be attributed to the quantum size effect of electrons and holes in small silicon nanocrystals (about 2 nm). The size of silicon nanocrystals is determined by analyzing Raman spectra, and it is consistent with estimates obtained from photoluminescence data.     

Localized donor-acceptor pairs of fluorophores: Determination of the energy transfer rate by nonlinear fluorimetry

A laser fluorescence method has been developed for determining the energy transfer rate. It is based on the model of collective states of localized donor-acceptor pairs of fluorophores proposed in our previous work and involves nonlinear fluorimetry (other photophysical parameters of the donor and acceptor are simultaneously determined). The proposed approach has been tested on mRFP1 fluorescent (red) protein.     

Self-similar solution of the Navier-Stokes equations for a completely ionized hydrogen plasma (the plane piston problem)

The self-similar motion of a completely ionized hydrogen plasma is considered in the two-temperature hydrodynamic approximation, i.e., we consider the plane piston problem and the problem on energy release at a fixed wall. Results obtained by numerical integration of the relevant system of ordinary differential equations are quoted.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, Vol. 10, No. 3, pp. 34–39, May–June, 1969.     

Switchable Bifunctional Stimuli‐Triggered Poly‐N‐Isopropylacrylamide/DNA Hydrogels

DNA‐tethered poly‐N‐isopropylacrylamide copolymer chains, pNIPAM, that include nucleic acid tethers have been synthesized. They are capable of inducing pH‐stimulated crosslinking of the chains by i‐motif structures or to be bridged by Ag⁺ ions to form duplexes. The solutions of pNIPAM chains undergo crosslinking at pH 5.2 or in the presence of Ag⁺ ions to form hydrogels. The hydrogels reveal switchable hydrogel‐to‐solution transitions by the reversible crosslinking of the chains at pH 5.2 and the separation of the crosslinking units at pH 7.5, or by the Ag⁺ ion‐stimulated crosslinking of the chains and the reverse dissolution of the hydrogel by the cysteamine‐induced elimination of the Ag⁺ ions. The DNA‐crosslinked hydrogels are thermosensitive and undergo reversible temperature‐controlled hydrogel‐to‐solid transitions. The solid pNIPAM matrices are protected against the OH^? or cysteamine‐stimulated dissociation to the respective polymer solutions.     

Bistability of the system of nitrite utilization by Escherichia Coli: Analysis of a mathematical model

Some mathematical model is analyzed describing nitrite utilization by E. coli cells grown in a flow chemostat. The system is of interest from the standpoint of the analysis of the mechanisms by which a cell utilizes toxic substrates in respiration. It is demonstrated that the system admits the appearance of two stationary nitrite concentrations; thus, it becomes bistable. The range of the nitrite supply rate into the chemostat for which the model is bistable is determined. The model predicts the possibility of a spontaneous death of the culture in transition between stationary states.     

Generation of terahertz radiation by the axicon focusing of ionizing laser pulses

Experimental results on the generation of terahertz radiation in the gas breakdown by high-power quasi-monochromatic laser pulses focused by an axicon lens are presented. A theoretical model developed for the terahertzradiation generation includes the nonlinear interaction of a femtosecond pulse with an ionized gas and the excitation of transverse oscillations of the plasma column. The results of the theoretical analysis are compared with the experimental data.     

Intermolecular interactions in acetonitrile in a liquid and in a low-temperature argon matrix

IR spectra of acetonitrile embedded in an argon matrix and in a liquid are recorded. IR spectra of specimens obtained with different concentrations of acetonitrile in argon are analyzed. The spectral region of C≡N vibrations of 2200–2300 cm⁻¹ with bands of monomers and possible associates is investigated. Overlap with the band of a hot transition on the low-frequency side is responsible for the pronounced asymmetry of the band ν(C≡N). To whom correspondence should be addressed. St. Petersburg State Institute of Precision Mechanics and Optics (Technical University), 14, Sablinskaya Str., St. Petersburg, 197101, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 627–631, September–October, 1999.