Light propagation in chiral media with large pitch

Light propagation in uniaxial chiral media with large pitch is studied. In these systems there are forbidden zones for extraordinary beams, which lead to effective reflection on zone boundaries and to wave damping inside the forbidden zone. We analyze the vicinities of the turning points and the transition of an extraordinary wave through the forbidden zone. Narrow forbidden zones with merging turning points are studied in detail. The transition through the forbidden zone is studied experimentally in nematic liquid crystal doped with a chiral addition. There is a good agreement between experimental results and theoretical calculations.     

Ozone Solubility in Aqueous Solutions of NaCl,Na2SO4, and K2SO4: Application of the Weisenberger-Schumpe Model for Description of Regularities and Calculation of the Ozone Molar Absorption Coefficient

The ozone solubility in aqueous solutions of salts, NaCl (up to 5 М) and Na₂SO₄ (up to 2 М) and their mixtures, was studied. The results are adequately described by the semi-empirical model proposed by Weisenberger and Schumpe for calculation of the solubilities of atmospheric gases in concentrated solutions of electrolytes. By comparing the data obtained experimentally and calculated in terms of the Weisenberger and Schumpe model, the ozone molar absorption coefficient was found to be ε = 2860 ± 200 M^?1 cm^?1 at 260 nm.     

Electrostatic Mechanophores in Tuneable Light‐Emitting Piezopolymer Nanowires

Electromechanical coupling through piezoelectric polymer chains allows the emission of organic molecules in active nanowires to be tuned. This effect is evidenced by highly bendable arrays of counter‐ion dye‐doped nanowires made of a poly(vinylidenefluoride) copolymer. A reversible redshift of the dye emission is found upon the application of dynamic stress during highly accurate bending experiments. By density functional theory calculations it is found that these photophysical properties are associated with mechanical stresses applied to electrostatically interacting molecular systems, namely to counterion‐mediated states that involve light‐emitting molecules as well as charged regions of piezoelectric polymer chains. These systems are an electrostatic class of supramolecular functional stress‐sensitive units, which might impart new functionalities in hybrid molecular nanosystems and anisotropic nanostructures for sensing devices and soft robotics.     

Strength in numbers: probing and understanding intermolecular bonding with chemical force microscopy

Scanning probe microscopy (SPM) provided researchers with a simple, intuitive, and versatile tool for probing intermolecular interactions using SPM probes functionalized with distinct chemical species. Chemical force microscopy (CFM) was developed as a way to probe and map these interactions in a rational and systematic way. But does the rupture strength of a bond measured in these experiments provide the definitive and useful information about the interaction? The answer to this question is closely linked to understanding the fundamental physics of bond rupture under an external loading force. Even a simple model shows that bond rupture can proceed in a variety of different regimes. I discuss the approaches for extracting quantitative information about the interaction from these experiments and show that even though the measured rupture force is almost never unique for a given bond, force spectroscopy measurements can still determine the essential interaction parameters.     

Trajectory tracking control for robot manipulators using only position measurements

In the paper, the trajectory tracking control problem is investigated for robotic manipulators which are not equipped with the tachometers. Our contribution consists in establishing uniform asymptotic stability in closed-loop system by using the dynamic position-feedback controller with feedforward. Using Lyapunov vector function and comparison principle, we construct the non-linear controller with variable gain matrices and first-order linear dynamic compensator such that the origin of the closed-loop system is uniformly asymptotically stable. The controller is shown to be robust with respect to parameters incertainties. We illustrate the utility of our result by simulation tests with reference to a two-link planar elbow robot manipulator.     

Negative thermal expansion in one-dimension of a new double sulfate AgHo(SO4)2 with isolated SO4 tetrahedra

A double holmium-silver sulfate was obtained for the first time.The temperature intervals for the for-mation and stability of the compound were determined by differential scanning calorimetry.The crystal structure of AgHo(SO4)2 was determined by Rietveld method.The X-ray diffraction(XRD)analysis showed that the compound crystallizes in the monoclinic syngony,space group P21/m,with the unit cell param-eters a=4.71751(4)?,b=6.84940(6)? and c=9.89528(9)?,β=95.1466(4)°,V=318.448(5)?3,Z=2,RB=1.55％,T=303K.Two types of sulfate tetrahedra were found in the structure,which significantly affected the spectral properties in the infrared range.In the temperature range of 143-703 K,a negative thermal expansion along the b direction accompanied by a positive thermal expansion along the a and c directions was observed.It was established that negative thermal expansion is the result of the deforma-tion of sulfate tetrahedra,which is affected by the movement of holmium and silver atoms.The excitation in the blue spectral range(457.9 nm)produces a luminescence in light blue(489 nm),green(545 nm)and red(654 nm)spectral ranges,and the latter two were of comparable intensity that is favorable for WLED sources.The observed luminescent band distribution is ascribed to the specific crystal field at Ho3+ion sites rather than a variation of radiationless probability.     

Light‐Emitting Nanophotonic Designs Enabled by Ultrafast Laser Processing of Halide Perovskites

Nanophotonics based on resonant nanostructures and metasurfaces made of halide perovskites have become a prospective direction for efficient light manipulation at the subwavelength scale in advanced photonic designs. One of the main challenges in this field is the lack of large‐scale low‐cost technique for subwavelength perovskite structures fabrication preserving highly efficient luminescence. Here, unique properties of halide perovskites addressed to their extremely low thermal conductivity (lower than that of silica glass) and high defect tolerance to apply projection femtosecond laser lithography for nanofabrication with precise spatial control in all three dimensions preserving the material luminescence efficiency are employed. Namely, with CH₃NH₃PbI₃ perovskite highly ordered nanoholes and nanostripes of width as small as 250 nm, metasurfaces with periods less than 400 nm, and nanowire lasers as thin as 500 nm, corresponding to the state‐of‐the‐art in multistage expensive lithographical methods are created. Remarkable performance of the developed approach allows to demonstrate a number of advanced optical applications, including morphology‐controlled photoluminescence yield, structural coloring, optical‐ information encryption, and lasing.     

The impact of increasing environmental requirements on the efficiency of water utilities: Russian case

Clean Technologies and Environmental Policy - Improving the efficiency of water utilities is important for sustainable water use. If performance evaluation relies solely on quantitative results,...     

Towards macroporous phononic crystal based structures for FBAR applications. Theoretical investigation of technologically competitive solutions

Microsystem Technologies - The research work of current contribution is focused on the study of periodic macroporous arrangements, their designs scaling ability and performance depending on a...     

Simulation of Payload Vibration Protection by Shape Memory Alloy Parts

A system of vibroisolation under consideration consists of a payload connected to a vibrating housing by plane shape memory alloy (SMA) slotted elements. The calculation of the mechanical behavior of the SMA is based on a microstructural theory. Simulations of harmonic and of impact excitations are carried out. The results have shown that protective properties of this system depend on the SMA state. The maximum reduction of the acceleration amplitude for harmonic excitation is reached when the SMA is in the martensitic (pseudo-plastic) state or in the two-phase state. A variation of temperature allows changing the resonance frequency and thus escaping from the resonance and controlling a mode of vibration.