Raman study of low-frequency modes in three glycine polymorphs

The temperature dependence of selected low-wavenumber (< 200 cm(-1)) Raman bands was studied for the different crystalline phases (α-, β-, γ-) of glycine--the simplest possible "building block" of a biomolecule. The temperature dependence of the frequencies of vibrational modes deviates from the theoretical expectation based on the assumption of cubic anharmonicity. Although relatively small, this deviation was observed above 250 K for all the three polymorphs. This finding was discussed in relation to the "dynamical transition" phenomenon, observed in variety of biomolecules in the range 200-250 K. The similarity of the temperatures suggests, that the origin of the dynamical transition phenomenon can be related to intrinsic conformational states of biomolecules, while water serves rather as a plasticizer or a structure organizer.     

On stochastic orders of absolute value of order statistics in symmetric distributions

Let Y₁,…,Y_n be the order statistics of a simple random sample from a finite or infinite population, having median =M. We compare the variables |Y_j−M| and |Y_m−M|, where Y_m is the sample median, that is, for odd n. The comparison is in terms of the likelihood ratio order, which implies stochastic order as well as other orders. The results were motivated by the study of best invariant and minimax estimators for the k/N quantile of a finite population of size N, with a natural loss function of the type , where F_N is the population distribution function, t is an estimate, and g is an increasing function.     

Chirped-pulse adiabatic control in coherent anti-Stokes Raman scattering for imaging of biological structure and dynamics

Two novel control methods based on adiabatic passage are proposed to be implemented in coherent anti-Stokes Raman scattering (CARS) microscopy for noninvasive imaging of biological structure and dynamics. The first method provides optimal pulse-area control of the resonant vibrational transitions by using a pair of equally linear-chirped pulses. The second method, named the 'roof' method, utilizes the chirp sign variation at the central time and gives robust adiabatic excitation of the resonant vibrational mode. Both methods are robust with respect to suppression of the off-resonant transitions. The methods allow one to achieve chemical sensitivity with high resolution and can be used to obtain CARS spectra of biological molecules with efficiently suppressed background.     

Cross Section of Tritium Production in Structural Materials of Accelerator-Driven Facilities

Physics of Atomic Nuclei - Measured cross sections of the production of tritium in thin 27Al, natNi, and natW targets irradiated with protons with energies ranging from 40 to 2600 MeV are...     

On the universal regularities of the lattice dynamics in ferroelectrics

The main regularities revealed for the dynamic response in recent Raman spectroscopic investigations of ferroelectric crystals of the displacive type (LiNbO₃, LiTaO₃) and the order-disorder type (KDP, DKDP) are discussed. The characteristic feature of the dynamic response for all the crystals (KDP, DKDP, LiNbO₃, LiTaO₃) under investigation in the vicinity of the phase transition temperature is an intense central peak that follows from the theoretical predictions for the order-disorder phase transition. The possible factors responsible for the central peak, the character of the behavior of this peak outside the aforementioned temperature range, and the specific features of the behavior of the width and intensity of the central peak over a wide range of temperatures for order-disorder crystals are analyzed.     

Specific features of the central peak in the Raman spectra of a lithium niobate crystal

The low-frequency Raman scattering (RS) spectra of a LiNbO₃ ferroelectric crystal are studied in the temperature range 300–1423 K. The central peak characterizing the relaxation susceptibility of the crystal lattice is observed over the entire temperature range studied, including at temperatures much lower than the Curie temperature (T _c = 1470 K). Far from T _c, the characteristics of the central peak are shown to be unlike those expected in the framework of the standard approaches. (i) The central-peak width γ_R increases as the temperature increases to T ～ 1300 K, and the critical slowing down (γ_R ∝ T _c ? T) occurs only above this temperature. (ii) A central peak arises in the RS geometry where the scattering by “nonferroelectric” E phonons is allowed. The experimental results are interpreted with allowance for relaxation dynamics in local regions of the crystal lattice.     

Non-destructive measurements of natural radionuclides in building materials for radon entry rate assessment

Journal of Radioanalytical and Nuclear Chemistry - To control the specific activity of 226Ra in building materials of operated buildings, a non-destructive in situ method consisted in measurements...     

Sterrett Procedure for the Generalized Group Testing Problem

Methodology and Computing in Applied Probability - Group testing is a useful method that has broad applications in medicine, engineering, and even in airport security control. Consider a finite...     

Quantum phase control of entanglement

A method of phase control of entanglement in two-qubit systems is proposed. We show that by changing a relative phase of the pulses that drive the transitions in a two-qubit system with closed-loop couplings, one can control entanglement at will. The method relies on adiabatic dynamics via time-delayed pulse sequences and can be implemented with both resonant and nonresonant transitions.     

Investigation of amorphous states of SiO2 by Raman scattering spectroscopy

The vitreous SiO₂ samples irradiated with fast neutrons at a dose of 5×10¹⁷?2.2×10²⁰ per cm² are investigated by the Raman scattering technique. It is demonstrated that the maximum of the low-frequency Raman spectrum (boson peak) shifts with an increase in the irradiation dose, and the medium-range order size decreases from 25 Å for the initial glass to 19 Å for the sample subjected to irradiation at a maximum dose. It is revealed that the fast relaxation intensity obtained from analysis of the low-frequency Raman spectra linearly correlates with the specific volume of the studied samples.