<Superscript>2</Superscript>H NMR investigation of the transition to the proton glass state in the Cs<Subscript>5</Subscript>H<Subscript>3</Subscript>(SO<Subscript>4</Subscript>)<Subscript>4</Subscript> · 0.5H<Subscript>2</Subscript>O crystal

A crystal of the Cs₅H₃(SO₄)₄ · xH₂O (x ≈ 0.5) (PCHS) compound, which belongs to the family of proton conductors with a complex system of hydrogen bonds, is investigated by ²H NMR spectroscopy. The temperature and orientation dependences of the ²H NMR spectra are measured and analyzed. It is established that, upon transition to the glassy phase at the temperature T _g = 260 K, the parameters characterizing the proton exchange between positions in hydrogen bonds remain unchanged to within the limits of experimental error. The protons in the two-dimensional network of hydrogen bonds in the (001) plane are dynamically disordered over possible positions down to temperatures considerably lower than the glass transition point T _g . However, water molecules are fixed at particular structural positions in the phase transition range. In PCHS crystals with a nonstoichiometric water content, this circumstance can be responsible for the frustration that leads to the formation of the glassy state.     

Numerical simulation of the operation process and thrust performance of an air-breathing pulse detonation engine in supersonic flight conditions

Multidimensional simulations of the unsteady gasdynamic flow in the duct of an air-breathing pulse detonation engine (ABPDE) operating on propane gas and the flow around it in supersonic flight at Mach numbers M of 3.0 and an altitude of 9.3 and 16 km are performed. It is shown that, at a length and diameter of the duct of 2.12 m and 83 mm, respectively, an ABPDE with an air intake and a nozzle can operate in a cyclic mode at a repetition frequency of 48 Hz, with a rapid deflagration-to-detonation transition (DDT) occurring at a distance of 5–6 combustion chamber diameters. To determine the thrust performance of the ABPDE in flight conditions, a series of working cycles were simulated with consideration given to the external flow around the engine. Calculations showed that the specific impulse of the ABPDE is approximately 1700 s. This value is much higher than the specific impulse typical of ramjet engines operating on conventional combustion (1200–1500 s) and substantially lower than the specific impulse obtained for the atmospheric conditions at sea level at zero flight velocity (∼2500 s).     

Structure and functional properties of rapidly quenched ribbons of Ti<Subscript>2</Subscript>NiCu alloy with different fractions of the crystalline phase

The controllable annealing of amorphous Ti₂NiCu ribbons by a pulsed electric current was developed, and samples with different fractions of crystalline phase were obtained. The samples’ structure was studied using high-resolution electron microscopy. Annealing conditions allowing us to obtain an amorphous nanocrystalline structure with grain sizes of less than 10 nm were determined. Conditions for obtaining samples with the two-wave shape memory effect were found. A prototype micromanipulator was designed and successfully tested.     

Power-law autocorrelated stochastic processes with long-range cross-correlations

We develop a stochastic process with two coupled variables where the absolute values of each variable exhibit long-range power-law autocorrelations and are also long-range cross-correlated. We investigate how the scaling exponents characterizing power-law autocorrelation and long-range cross-correlation behavior in the absolute values of the generated variables depend on the two parameters in our model. In particular, if the autocorrelation is stronger, the cross-correlation is also stronger. We test the utility of our approach by comparing the autocorrelation and cross-correlation properties of the time series generated by our model with data on daily returns over ten years for two major financial indices, the Dow Jones and the S&P500, and on daily returns of two well-known company stocks, IBM and Microsoft, over five years.     

Suppression of decoherence in a wave packet via nonlinear resonance

We propose a simple approach for suppressing decoherence of a wave packet excited in an anharmonic oscillator. We show that when a resonant external field forces the oscillator to follow the driving force, motion around the resonant trajectory inside a stable resonant island can be made almost completely immune to the environment. As an example, we study suppression of decoherence due to coupling to thermally populated rotations in vibrational wave packets in a Na2 molecule.     

Charge accumulation in ultrathin Cs / n - GaN and Cs / n - InGaN interfaces

We report on the observation of new phenomena that arise under Cs adsorption on n-GaN(0001) and n-InGaN(0001) surfaces. First, an extremely highly quantum efficient photoemission has been found by excitation with visible light in the transparency region of GaN and InGaN. The photoemission is revealed to appear due to the formation of an electron accumulation layer in the vicinity of the surfaces. Second, a large variety of band bending and potential wells are provided by the Cs coverages. The accumulated charge density at the n-InGaN surface is much stronger than that at the n-GaN surface. Third, a new effect is revealed, namely, the appearance of an oscillation structure in the spectral dependences of the threshold photoemission. A model concept is proposed for photocurrent oscillations that takes into account the formation of an accumulation layer and the multiple-beam interference in parallel-sided GaN or InGaN samples.     

Anharmonic Bloch Oscillation of Electrons in Biased Superlattices

The oscillatory motion of electrons in a periodic potential under a constant applied electric field, known as Bloch oscillations (BO), is one of the most striking and intriguing quantum effects and was predicted more than eighty years ago. Oscillating electrons emit electromagnetic radiation and here we consider this BO effect for emission in the THz region. To date, it has been assumed that the Bloch oscillation of an electron is anharmonic oscillation, therefore with radiation emitted at the single Bloch frequency. We analyze scenarios when Bloch oscillations can be accompanied by the emission of radiation not only at the Bloch frequency but also with double and triple Bloch frequencies. The first scenario means that electrons could jump over neighboring Stark states. The second scenario of anharmonic emission is coupled to an opening of the minigap in the miniband.     

Influence of cascading phenomena on a type I second-harmonic wave generated by an intense femtosecond pulse: application to the measurement of the effective second-order coefficient

We have studied the influence of cascaded second-order effects on the spectral density of a second-harmonic pulse generated in thin KDP and beta-barium borate crystals by an intense femtosecond pulse. A noticeable evolution of spectral density is recorded for any value of phase mismatch. This evolution is in good agreement with the solution of the nonlinear propagation equation and allows a simple direct measurement of the effective susceptibility of the studied crystals.     

On the size effect in nanocrystalline cerium dioxide: Is the Tsunekawa model correct?

Nanocrystalline cerium-dioxide samples with different coherent-scattering region sizes are analyzed by advanced techniques, specifically, small-angle neutron scattering, X-ray and neutron diffraction, and spectrometry of the chemical shift in the characteristic X-ray lines. The obtained data confirm the presence of the size effect, i.e., the dependence of lattice constants on the size of coherent-scattering regions. Meanwhile, no traces of oxygen nonstoichiometry and a related deviation in the effective degree of cerium oxidation from the standard value are found. The results obtained call into question the Tsunekawa model traditionally used to explain the size effect in this compound.