Porous Silicon Photonic Crystal as a Substrate for High Efficiency Biosensing

Photonic crystals offer great possibilities for the improvement of performance of different kinds of devices. Due to the ability to control the light propagation and to change optical properties via interaction with the media photonic crystals have been widely used to increase the sensitivity of biosensing in many experimental setups. Among them some of the most interesting for practical applications are one-dimensional porous silicon photonic crystals. They could be easily fabricated, have big surface area, high sorption abilities, and have been shown to be able to change the emission of embedded luminophores. In this study we have fabricatedand performed the comprehensive investigation of the properties of hybrid system consisting of the porous silicon one-dimensional photonic crystals embedded with semiconductor quantum dots as the luminophores. We have demonstrated the ability of these systems to enhance the photoluminescence of luminophores and serve as the substrate for the high efficient biosensing. Keywords: Porous silicon, microcavity, quantum dots, luminescence enhancemen

Modeling and Optimization of the Porous Silicon Photonic Structures

Photonic crystals and optical devices based on them are of great interest nowadays and are widely used in photonics, optoelectronics, and biosensing. One of the most practically using materials to fabricate one-dimensional photonic crystal is porous silicon due to the simple fabrication process, high porosity and ability to select precisely the refractive index by controlling the porosity. It has already been shown as the suitable material to be used as an element of many photonic devices including gas sensors and biosensors. However, because of the complicated porous structure, and silicon oxidation, occurring at the atmosphere conditions, optical properties of porous silicon photonic structures need to be stabilized by preventive oxidation. In order to predict eventual optical properties of fabricated photonic structures an adequate modeling should be performed. In our study we have developed a calculation model based on the combination of effective media approximations and transfer matrix method, which could precisely predict the reflection, transmission of the porous silicon photonic structures taking into account the dispersion of the refractive index of silicon and silicon oxide, and the oxidation degree. We also used numerical finite-difference time-domain calculations in order to investigate the luminescent properties of the lumiphores embedded into the porous photonic structure. Keywords: Porous silicon, microcavity, transfer matrix, effective media, FDT

Nonsteady condensation and evaporation waves

We study motion of a phase transition front at a constant temperature between stable and metastable states in fluids with the universal Van der Waals equation of state (which is valid sufficiently close to the fluid's critical point). We focus on a case of relatively large metastability and low viscosity, when it can be shown analytically that no steadily moving phase-transition front exists. Numerically simulating a system of the one-dimensional Navier-Stokes and continuity equations, we find that, in this case, the nonsteady phase-transition front emits acoustic shocks in forward and backward directions. Through this mechanism, the front drops its velocity and eventually comes to a halt. The acoustic shock wave may shuttle, bouncing elastically from the system's edge and strongly inelastically from the phase transition front. Nonsteady rarefaction shock waves appear in the shuttle process, despite the fact that the model does not admit steady rarefaction waves propagating between stationary states. If the viscosity is below a certain threshold, an instability sets in, driving the system into a turbulent state. This work was supported by the Japan Society for Promotion of Science.Comment: revtex text file and four eps files with figures. Physical Review Letters, in pres

Highly Stable, Water-Soluble CdSe/ZnS/CdS/ZnS Quantum Dots with Additional SiO2 shell

Quantum dots (QDs) are fluorescent nanocrystals extensively used today in research and applications. They attract much interest due to the high photostability and fluorescence quantum yields close to 100%. The best QDs are made by synthesis in organic media, and they have to be transferred into aqueous solutions if biomedical applications are concerned. An advanced method for rendering QDs water-soluble is to coat them with hydrophilic SiO2 -layer. However, growing a silica shell with a predetermined thickness is a problem, because uncertain values of the molar extinction coefficients (ε) of core/shell QDs made it impossible to calculate precise yields of the chemical reactions involved. Here we suggest an approach to solving this problem by constructing the structural models of per se and silica-coated QDs followed by measuring ε in a course of the QD synthesis, thus carrying out precise quantitative reactions. Proceeding in such a way, we prepared the CdSe/ZnS/CdS/ZnS QDs with the structure predicted by the model and coated by silica shell. Prepared QDs are characterized by a narrow size distribution and the same fluorescence parameters as the original QDs in the organic medium. Developed approach permitted efficient QDs water-solubilisation and preparation of stable nanoparticles for plethora of biomedical applications.     Keywords: Quantum dots, QD, silica shell, core-shel

Применение моделирования при проектировании инструмента для прессования полых профилей из алюминиевых сплавов

In order to simulate the pressing of hollow profiles made from aluminum alloys, the previously developed design algorithms for the pressing tool and the QForm software were utilized. The objective of this study was to enhance the quality and decrease the design timeintervals for pressing tools used in the industrial production of aluminum alloy profiles. A novel design procedure for a combined tool, along with the technology of semi-continuous pressing with welded hollow profiles made from aluminum alloys, was proposed. This was achieved using the QForm software, which enables efficient calculations and adjustments of pressing parameters and tool geometry through a dialog interface. The developed algorithm and design procedures enable the drawing of hollow profiles, technological calculations of pressing parameters, selection of a suitable horizontal hydraulic press, matrix and splitter design, determination of strength parameters, assessment of equipment load, and preparation of working drawings for the pressing tool. In order to validate the effectiveness of the design procedure, it was applied to typical hollow profiles fabricated on a commercial scale. Two variations of the pressing tool design were examined. Simulation results obtained from QForm Extrusion software, specifically designed for pressing analysis, revealed that the initial design of the tool, with predetermined technological parameters and geometry of the splitter and matrix channels, resulted in uneven flow of profile elements and temperature distribution. However, by adjusting the tool parameters, it was possible to achieve a straight profile exit from the matrix and a uniform temperature distribution across its cross section. Industrial verification of the designed tool, utilizing a 33 MN hydraulic horizontal press for pressing profiles made from alloy 6063, demonstrated that significant modifications to the matrix and splitter were not necessary. By employing the proposed pressing tool design, batches of products were successfully manufactured in compliance with the required technical specifications, while reducing the design time intervals of the pressing tool by approximately 50 %.Для моделирования процесса прессования полых профилей из алюминиевых сплавов использованы разработанные ранее алгоритмы проектирования прессового инструмента и программный комплекс «QForm». Целью проведенных исследований являлось повышение качества и снижение сроков проектирования прессового инструмента для промышленных условий производства профилей из алюминиевых сплавов. Предложены новая методика проектирования комбинированного инструмента и технологии для полунепрерывного прессования со сваркой полых профилей из алюминиевых сплавов с помощью программного комплекса «QForm», который позволяет в диалоговом режиме оперативно проводить многовариантные расчеты с последующей, если необходимо, корректировкой технологических параметров прессования и геометрии инструмента. Созданы алгоритм и процедуры проектирования, которые дают возможность выполнить чертеж полого профиля, осуществить технологические расчеты параметров прессования и выбор горизонтального гидравлического пресса, спроектировать матрицу и рассекатель, провести прочностные расчеты, определить силовую загрузку оборудования и подготовить рабочие чертежи прессового инструмента. Для проверки работоспособности разработанной методики проектирования приведен пример ее реализации для одного из типовых полых профилей, изготавливаемого в промышленном производстве. Рассмотрено проектирование двух вариантов прессового инструмента. С помощью моделирования с использованием программы «QForm Extrusion», предназначенной для анализа процессов прессования, установлено, что первый вариант конструкции инструмента при заданных технологических параметрах и геометрии каналов рассекателя и матрицы приводит к неравномерности истечения различных элементов профиля и температур. В результате проведенной корректировки параметров инструмента удалось добиться прямолинейности выхода профиля из матрицы и равномерности распределения температур по его сечению. Промышленное опробование спроектированного инструмента на гидравлическом горизонтальном прессе с усилием 33 МН для прессования профиля из сплава 6063 показало, что существенной доработки матрицы и рассекателя не требуется. С применением предложенной конструкции прессового инструмента получены партии продукции, соответствующей требованиям действующих технических условий, при этом сроки проектирования прессового инструмента сокращены практически в 2 раза

Экспериментальное определение и сравнительный анализ характеристик прочности полимеров PPH030GP, ABS и PLA при различных скоростях деформации

Nowadays the field of application of products made from polymer materials is constantly increasing. These products find their wide application in the most high-tech industries such as automotive, aerospace and medical industry. Modern trends in the development of the automotive industry predicts that 75 % of the total car mass will be replaced with polymer materials by 2020 and other industries demonstrate similar trends. Regarding to this information, engineering companies that design parts of the automotive industry should have polymer material characteristics over an entire range of deformations up to destruction for their performance prediction. However, strength characteristics of products from polymers are different and depend not only on a polymer grade but also on technology used for part production. Existing literature review on this problematic area is rather rare. The purpose of this paper is to determine and analyze mechanical characteristics of widely used PPH030GP polymer obtained by extrusion and ABS, PLA polymers applied while manufacturing samples using an additive method (3D-printing) depending on the rate of high-elastic deformation. All the samples have been made according to the requirements of GOST 11262–80 and subjected to uniaxial stretching on a tensile machine UIT STM 050/300 at different speeds of clamp expansion. According to experimental results, stretching diagrams in conditional coordinates s–e have been obtained up to the point of failure for different rates of clamp expansion. It has been shown that while using the additive method, a direction of layers and adhesion between them, which depends on 3D-print parameters, have a significant effect on the part strength. Printing settings are indicated in accordance with the selected mode and a 3D-printer model. As a result of data processing, strength characteristics of PPH030GP polymer and ABS and PLA polymers have been determined to a sufficient extent, depending on the direction of printing layers and rate of high-elastic deformation. These data can be used to calculate strength of products by numerical methods and a finite element method in various software products.Сегодня область применения изделий из полимерных материалов постоянно увеличивается. Такие изделия находят широкое применение в наиболее наукоемких отраслях, таких как автомобильная, аэрокосмическая и медицинская отрасли. Современные тенденции развития автомобильной промышленности прогнозируют к 2020 году 75 % общей массы автомобиля заменить полимерными материалами. Схожие тренды демонстрируют и другие отрасли. В связи с этим инженерным компаниям, проектирующим детали автомобильной промышленности, для прогнозирования их работоспособности необходимо иметь характеристики полимерных материалов во всем диапазоне деформаций – вплоть до разрушения. Однако прочностные характеристики изделий из полимеров различны и зависят не только от марки полимера, но и от технологии производства детали. Подробная информация в отечественной литературе встречается достаточно редко и в сжатом виде. Авторами статьи была поставлена задача определить и проанализировать механические характеристики широко применяемого полимера PPH030GP, полученного экструзивным методом, и полимеров ABS и PLA, применяемых при изготовлении образцов аддитивным методом (3D-печать) в зависимости от скорости деформации. Для этого были выполнены образцы согласно требованиям ГОСТ 11262–80 и подвергнуты одноосному растяжению на разрывной машине UIT STM 050/300 при разных скоростях раздвижения зажимов. По результатам экспериментальных исследований получены диаграммы растяжения в условных координатах s–e вплоть до момента разрушения для различных скоростей раздвижения зажимов. Показано, что при аддитивном методе значительное влияние на прочность изделия оказывают направление слоев и адгезия между ними, которая зависит от параметров 3D-печати. Параметры печати указаны в зависимости от выбранного режима и конструкции 3D-принтера. В результате обработки данных в достаточно полной мере определены прочностные характеристики полимеров PPH030GP, ABS и PLA в зависимости от направления слоев печати и скорости деформации. Эти данные можно применять для расчета прочности изделий численным методом и методом конечных элементов в различных программных продуктах

Fine-tuning of Silica Coating Procedure for Preparation of Biocompatible and Bright Pbs/Sio2 Qds

Near-infrared semiconductor PbS quantum dots (QDs) with emission in biological transparency window are promising material for in vivo biolabelling and deep-tissue imaging of biological specimen. Among various approaches that render initially hydrophobic and toxic QDs biocompatible, the growth of a silica shell on the QD surface represents an efficient method to minimize QD toxicity. Nevertheless, it is important to preserve QDs emission properties after the silica coating procedure. Here we report on the optimal parameters of this procedure which allow to obtain a stable silica shell and maintain the optical properties of initial PbS QDs. Furthermore, we show that PbS QDs with the optimal SiO2 shell retain their luminescence quantum yield even after condensation into a solid film. Thus, our procedure can become a basis in development of bright, receptor-targeted NIR fluorescent probes for in vivo tumor imaging. Keywords: quantum dot, SiO2 shell, bioimagin