Numerical model of hybrid mode-locked Tm-doped all-fibre laser

Abstract: Ultrafast Tm-doped fibre lasers have been actively studied for the last decade due to their potential applications in precise mid-IR spectroscopy, LIDARs, material processing and more. The majority of research papers is devoted to the comparison between a numerical modelling and experimental results; however, little attention is being paid to the comprehensive description of the mathematical models and parameters of the active and passive components forming cavities of Tm-doped all-fibre lasers. Thus, here we report a numerical model of a stretched-pulsed Tm-doped fibre laser with hybrid mode-locking and compare it with experimental results. The key feature of the developed numerical model is employment of the experimentally measured dispersion coefficients and optimisation of some model parameters, such as the bandwidth of the spectral filter spectral filtering and the saturation power of the active fibre, for a conformity with the experiment. The developed laser emits 331.7 fs pulses with a 23.8 MHz repetition rate, 6 mW of average power, 0.25 nJ of pulse energy, and a 21.66 nm spectral bandwidth at a peak wavelength of 1899.5 nm. The numerical model characteristics coincide with experimentally achieved spectral width, pulse duration, and average power with inaccuracy of 4.7%, 5.4%, and 22.9%, respectively. Moreover, in the discussion of the work the main possible reasons influencing this inaccuracy are highlighted. Elimination of those factors might allow to increase accuracy even more. We show that numerical model has a good agreement with the experiment and can be used for development of ultrafast Tm-doped fibre laser systems

All-Glass Single-Mode Leakage Channel Microstructured Optical Fibers with Large Mode Area and Low Bending Loss

The paper presents the results of theoretical and experimental studies of all-glass leakage channel microstructured optical fibers (MOFs) with a large mode area and low bending losses. These MOFs contain two layers of fluorine-doped silica glass elements with a reduced refractive index, different diameters, and different distances between them. A numerical analysis of the properties of these MOFs was performed using the finite element method. The leakage losses for the fundamental and higher-order modes were calculated in the spectral range from 0.65 μm to 1.65 μm. Simulation results show that the proposed MOF design allows for single-mode guidance in the spectral range from 0.92 μm to 1.21 μm with a bending radius of down to 0.08 m. The measured losses of the fabricated MOF with a core diameter of 22.5 μm and a bending radius of 0.1 m were less than 0.1 dB/m in the spectral range from 0.9 μm to 1.5 μm. It is demonstrated that the segments of this MOF longer than 5 m are single-mode

Extended defects in natural diamonds: Atomic Force Microscopy investigation

Surfaces of natural diamonds etched in high-pressure experiments in H2O, CO2 and H2O-NaCl fluids were investigated using Atomic Force Microscopy. Partial dissolution of the crystals produced several types of surface features including the well-known trigons and hillocks and revealed several new types of defects. Besides well-known trigons and dissolution hillocks several new types of defects are observed. The most remarkable ones are assigned to anelastic twins of several types. The observation of abundant microtwins, ordering of hillocks and presence of defects presumably related to knots of branched dislocations suggests importance of post-growth deformation events on formation of diamond microstructure. This work confirms previous reports of ordering of extended defects in some deformed diamonds. In addition, the current work shows that natural diamonds deform not only by dislocation mechanism and slip, but also but mechanical twinning. The dominant mechanism should depend on pressure-temperature-stress conditions during diamond transport from the formation domain to the Earth surface.Comment: Submitted to special issue (1st European Mineralogical congress, Frankfurt, Germany, September 2012) of European Journal of Mineralogy. 21 page, 9 figure

Investigation of the Effect of Substrate Orientation on the Structural, Electrical and Optical Properties of n-type GaAs1-xBix Layers Grown by Molecular Beam Epitaxy

Current-Voltage (I-V), Capacitance-Voltage (C-V), Deep Level Transient Spectroscopy (DLTS), Laplace DLTS, Photoluminescence (PL) and Micro-Raman techniques have been employed to investigate the effect of the orientation of the substrates on the structural, electrically and optically active defects in dilute GaAs1−xBix epilayers structures having a Bi composition x = ~5.4%, grown by Molecular Beam Epitaxy (MBE) on (100) and (311)B GaAs planes. X-ray diffraction results revealed that the in-plane strain in the Ga(As,Bi) layer of the samples grown on (100)-oriented substrate (−0.0484) is significantly larger than that of the samples grown on (311)B-oriented substrate. The substrate orientation is found to have a noticeable impact on the Bi incorporation and the electrical properties of dilute GaAsBi Schottky diodes. The I-V characteristics showed that (100) Schottky diodes exhibited a larger ideality factor and higher barrier height compared with (311)B samples. The DLTS measurements showed that the number of electrically active traps were different for the two GaAs substrate orientations. In particular, three and two electron traps are detected in samples grown on (100) and (311)B GaAs substrates, respectively, with activation energies ranging from 0.12 to 0.41 eV. Additionally, one hole trap was observed only in sample grown on (100) substrates with activation energy 0.24 eV. The observed traps with small activation energies are attributed to Bi pair defects. The photoluminescence (PL) and Raman spectra have evidenced different compressive strain which affects considerably the optical properties. Furthermore, the PL spectra were also affected by different contributions of Bi- related traps which are different for different substrate orientation in agreement with DLTS results

Рентгеноморфометрия как составляющая планирования вертебропластики при остеопорозе

The aim: to improve the outcomes of vertebroplasty of the vertebral bodies in osteoporosis based on the evaluation of X-ray results morphometry. Material and methods. Observation of 267 patients who have undergone spondilography thoracic and lumbar spine and computerized tomographic examination before and just after vertebroplasty, as well as 1 and 2 years after it. Vertebroplasty was performed by the standard technique and with the use of the proposed method. Results. Following the results of the X-ray morphometry of thoracic and lumbar vertebrae in patients with osteoporosis, the position was formulated concerning the necessity to strengthen the anterior and posterior segments of damaged vertebra body in all variations of its deformation. Insulated filling with polymer at the optimal level in case of 2-fragment type of vertebral body fracture allows to achieve reliable stabilization and avoid iatrogenic complications associated with extravertebral output of polymethylmethacrylate. Conclusion. In order to achieve persistent positive results of treatment of patients with uncomplicated fractures of vertebral bodies of the thoracic and lumbar the background affected by osteoporosis when planning to perform vertebroplasty it is necessary to take into consideration X-ray morphometry parameters of the damaged vertebra.Цель исследования: обоснование необходимости использования рентгеноморфометрии для улучшения исходов выполнения вертебропластики тел позвонков на фоне остеопороза. Материал и методы. Под наблюдением находилось 267 больных, которым выполняли спондилографию грудного и поясничного отделов позвоночника и компьютерно-томографическое обследование до и непосредственно после вертебропластики, а также через 1 и 2 года. Вертебропластику осуществляли по общепринятой методике и с использованием предложенного способа. Результаты. Учитывая результаты рентегноморфометрии грудных и поясничных позвонков у больных с остеопорозом, было сформулировано положение о необходимости укрепления переднего и заднего отделов тела поврежденного позвонка при всех вариантах его деформаций. Изолированное заполнение полимером в оптимальных объемах при двухфрагментарном типе перелома тела позвонка позволяет достичь его надежной стабилизации и избежать ятрогений, связанных с экстравертебральным выходом полиметилметакрилата. Выводы. Для достижения стойких положительных результатов лечения больных с неосложненными переломами тел позвонков грудного и поясничного отделов на фоне остеопороза при планировании выполнения вертебропластики необходимо учитывать рентгеноморфометрические параметры поврежденного позвонка

Diversification of Russian gas export routes

The exportation of energy (i.e., gas) resources plays a vital role in the economic development in Russia. The major market for Russian gas exports is Western Europe, which has caused a considerable amount of concern amongst Russian officials. This paper presents different options for gas export routes for Russia and other CIS countries, taking into account market demand and supply, as well as future price developments in Europe and Asia. The approach is based on a system of dynamic interregional optimisation models for the gas industry. The models describe possible alternatives for the development of the gas sector, in combination with options for economic relations within the gas industry, while taking into account financial conditions of the main market players. The main finding is that gas companies in Russia and CIS countries can diversify their export routes to Asian markets, which could become as important as the European market in view of the higher export prices.natural gas industry; energy market; energy prices; gas export; pipelines; Russia.

Quantitative Assessment of Chirality of Protein Secondary Structures and Phenylalanine Peptide Nanotubes

In this study we consider the features of spatial-structure formation in proteins and their application in bioengineering. Methods for the quantitative assessment of the chirality of regular helical and irregular structures of proteins are presented. The features of self-assembly of phenylalanine (F) into peptide nanotubes (PNT), which form helices of different chirality, are also analyzed. A method is proposed for calculating the magnitude and sign of the chirality of helix-like peptide nanotubes using a sequence of vectors for the dipole moments of individual peptides

Molecular Dynamics Simulation of the Thermal Behavior of Hydroxyapatite

Hydroxyapatite (HAP) is the main mineral component of bones and teeth. Due to its biocompatibility, HAP is widely used in medicine as a filler that replaces parts of lost bone and as an implant coating that promotes new bone growth. The modeling and calculations of the structure and properties of HAP showed that various structural defects have a significant effect on the properties of the material. By varying these structural heterogeneities, it is possible to increase the biocompatibility of HAP. An important role here is played by OH group vacancies, which are easily formed when these hydroxyl groups leave OH channels of HAP. In this case, the temperature dependence of the concentration of OH ions, which also determines the thermal behavior of HAP, is important. To study the evaporation of OH ions from HAP structures with increasing temperatures, molecular dynamics simulation (MDS) methods were used in this work. As a program for MDS modeling, we used the PUMA-CUDA software package. The initial structure of HAP, consisting of 4 × 4 × 2 = 32 unit cells of the hexagonal HAP phase, surrounded by a 15-Å layer of water was used in the modelling. Multiple and statistically processed MDS, running calculations in the range of 700–1400 K, showed that active evaporation of OH ions begins at the temperature of 1150 K. The analysis of the obtained results in comparison with those available in the literature data shows that these values are very close to the experiments. Thus, this MDS approach demonstrates its effective applicability and shows good results in the study of the thermal behavior of HAP

Molecular Dynamics Simulation Study of the Self-Assembly of Phenylalanine Peptide Nanotubes

In this paper, we propose and use a new approach for a relatively simple technique for conducting MD simulation (MDS) of various molecular nanostructures, determining the trajectory of the MD run and forming the final structure using external force actions. A molecular dynamics manipulator (MD manipulator) is a controlled MDS type. As an example, the applicability of the developed algorithm for assembling peptide nanotubes (PNT) from linear phenylalanine (F or Phe) chains of different chirality is presented. The most adequate regimes for the formation of nanotubes of right chirality D from the initial L-F and nanotubes of left chirality L of their initial dipeptides D-F modes were determined. We use the method of a mixed (vector–scalar) product of the vectors of the sequence of dipole moments of phenylalanine molecules located along the nanotube helix to calculate the magnitude and sign of chirality of self-assembled helical phenylalanine nanotubes, which shows the validity of the proposed approach. As result, all data obtained correspond to the regularity of the chirality sign change of the molecular structures with a hierarchical complication of their organization