The effect of growth atmosphere and Ir contamination on electric properties of La<Subscript>3</Subscript>Ta<Subscript>0.5</Subscript>Ga<Subscript>5.5</Subscript>O<Subscript>14</Subscript> single crystal grown by the floating zone and Czochralski method

The influence of growth atmosphere and Ir contamination on electrical resistivity of langatate (La₃Ta_0.5Ga_5.5O₁₄; LTG) was studied. LTG single crystals were grown via the Czochralski method under different oxygen partial pressures with Ir contamination from the Ir crucible. In addition, LTG crystals were grown by the floating zone method and they were not contaminated by Ir. The electrical resistivity and ionic transport number of these crystals were measured in the temperature range 300–1000°C. The conduction mechanism of LTG changed at about 720°C. At T < 720°C, electronic conduction was dominant, and the resistivity was affected by growth atmosphere as well as Ir contamination. In contrast, at T > 720°C, ionic conduction was dominant, and the resistivity was affected only by Ir contamination. In both temperature regions, Ir contamination decreased the resistivity by an order of magnitude.     

Bose-Einstein condensation and superfluidity of trapped polaritons in graphene and quantum wells embedded in a microcavity

The theory for spontaneous coherence of short-lived quasiparticles in two-dimensional excitonic systems is reviewed, in particular, quantum wells (QWs) and graphene layers (GLs) embedded in microcavities. Experiments with polaritons in an optical microcavity have already shown evidence of Bose-Einstein condensation (BEC) in the lowest quantum state in a harmonic trap. The theory of BEC and superfluidity of the microcavity excitonic polaritons in a harmonic potential trap is presented. Along the way, we determine a general method for defining the superfluid fraction in a two-dimensional trap, within the angular momentum representation. We discuss BEC of magnetoexcitonic polaritons (magnetopolaritons) in a QW and GL embedded in an optical microcavity in high magnetic field. It is shown that Rabi splitting in graphene is tunable by the external magnetic field B, while in a QW the Rabi splitting does not depend on the magnetic field in the strong B limit.     

Predicting retention time shifts associated with variation of the gradient slope in peptide RP-HPLC

We have developed a sequence-specific model for predicting slopes (S) in the fundamental equation of linear solvent strength theory for the reversed-phase HPLC separation of tryptic peptides detected in a typical bottom-up-proteomics experiment. These slopes control the variation in the separation selectivity observed when the physical parameters of chromatographic separation, such as gradient slope, flow rate, and column size are altered. For example, with the use of an arbitrarily chosen set of tryptic peptides with a 4-times difference in the gradient slope between two experiments, the R(2)-value of correlation between the observed retention times of identical species decreases to ~0.993-0.996 (compared to a theoretical value of ~1.00). The observed retention time shifts associated with variations of the gradient slope can be predicted a priori using the approach described here. The proposed model is based on our findings for a set of synthetic species (Vu, H.; Spicer, V.; Gotfrid, A.; Krokhin, O. V. J. Chromatogr., A, 2010, 1217, 489-497), which postulate that slopes S can be predicted taking into account simultaneously peptide length, charge, and hydrophobicity. Here we extend this approach using an extensive set of real tryptic peptides. We developed the procedure to accurately measure S-values in nano-RP HPLC MS experiments and introduced sequence-specific corrections for a more accurate prediction of the slopes S. A correlation of ~0.95 R(2)-value between the predicted and experimental S-values was demonstrated. Predicting S-values and calculating the expected retention time shifts when the physical parameters of separation like gradient slope are altered will facilitate a more accurate application of peptide retention prediction protocols, aid in the transfer of scheduled MRM (SRM) procedures between LC systems, and increase the efficiency of interlaboratory data collection and comparison.     

New trends in solar photovoltaics: From physics to chemistry

The paper briefly discusses the current situation in the field of traditional and unconventional photovoltaic materials and solar cells. It emphasizes the fact that the main basic achievements in the field of solid-state solar photovoltaics were gained at least two decades ago and the further progress focused on the improvement of cell parameters and technological aspects. Finally, the article concludes that this scientific area has nearly fulfilled its historical task. Indeed, the last decade has brought many new achievements in the field of the alternative, molecular-based materials. The future of solar energy conversion seems to be mainly connected with chemistry, chemical physics and chemical engineering but not with solid-state physics as in the twentieth century. The paper gives also a short over-view of some promising organic semiconductors, fullerenes and TiO₂ nanocrystalline structures used now in a new generation of molecular solar cells. Presented at the Int’l Symp. on Chem. Eng. (Cheju, Feb. 8–10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University     

Tailoring the diameter of single-walled carbon nanotubes for optical applications

Single-walled carbon nanotubes (SWCNTs) with specific diameters are required for various applications particularly in electronics and photonics, since the diameter is an essential characteristic determining their electronic and optical properties. In this work, the selective growth of SWCNTs with a certain mean diameter is achieved by the addition of appropriate amounts of CO₂ mixed with the carbon source (CO) into the aerosol (floating catalyst) chemical vapor deposition reactor. The noticeable shift of the peaks in the absorption spectra reveals that the mean diameters of the as-deposited SWCNTs are efficiently altered from 1.2 to 1.9 nm with increasing CO₂ concentration. It is believed that CO₂ acts as an etching agent and can selectively etch small diameter tubes due to their highly curved carbon surfaces. Polymer-free as-deposited SWCNT films with the desired diameters are used as saturable absorbers after stamping onto a highly reflecting Ag-mirror using a simple dry-transfer technique. Sub-picosecond mode-locked fiber laser operations at ∼1.56 μm and ∼2 μm are demonstrated, showing improvements in the performance after the optimization of the SWCNT properties.      

The adaptive algorithm of information unmistakable embedding into digital images based on the discrete Fourier transformation

Multimedia Tools and Applications - Many effective methods of the data embedding into digital images are based on the frequency transformations. However use of similar transformations is connected...     

Verformungsanalyse elektrisch leitender metallischer Bauteile bei Magnetimpulsbearbeitung

In the present study the deformation of conductive metallic systems under the action of electromagnetic fields is investigated. For this purpose, a variational formulation is introduced. The coupling of the propagation of electromagnetic fields and the deformation is taken into account by the introduction of electromagnetic forces. The suggested model allows the numerical analysis of the deformation of electrically conductive metallic systems under magnetic pulse processing.     

Chemical Vapor Synthesis of Titanium Aluminides by Reaction of Aluminum Subchloride and Titanium Tetrachloride

A new process for developing titanium aluminides (TiAls) using chemical vapor synthesis was investigated in a laboratory experiment. Aluminum subchloride (AlCl) was used as the reducing agent in the reaction with TiCl₄ and the source of aluminum for Ti-Al alloy. Two types of products, with large crystals and fine particles, were fabricated. The large crystals were determined to be TiAl, with small amounts of Ti and Ti₃Al phases. The composition of fine particles, on the other hand, varied in wide range.     

Surface and Subsurface Defects Studies of Dental Alloys Exposed to Sandblasting

The defects created in commercial dental alloys during blasting with alumina particles propelled in compressed air under pressure 0.1 and 0.4 MPa have been studied using positron annihilation spectroscopy, scanning electron microscopy and X-ray diffraction. It was observed that higher pressure causes the increase in roughness and damaged zone range. The type of defects was determined as vacancies on dislocations. The defect concentration decreases with the depth and depends on alloys' type and applied pressure. The Rutherford backscattering spectroscopy and variable energy positron beam studies indicate shallow alumina deposition in material and show that small pressure of 0.1 MPa is not enough to remove metal surface oxides completely in 60 s in all studied dental alloys.