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

ЭФФЕКТИВНЫЕ ШПОНОЧНЫЕ СОЕДИНЕНИЯ МНОГОПУСТОТНЫХ ПЛИТ ПЕРЕКРЫТИЙ СО СТЕНАМИ В СОВРЕМЕННОМ КРУПНОПАНЕЛЬНОМ ДОМОСТРОЕНИИ

The paper considers large-panel constructive system of multi-storey buildings and its industrial basis creates conditions for intensive volume growth in house construction. Application of hollow-core panels are recommended as floor slabs that allows to increase a distance between bearing walls, to improve planning solutions, and also significantly to increase thermal and sound protection properties of floor discs (coatings). Keyed joints having the highest resistance to shearing forces are used to ensure joint action of the slabs with wall panels. A supporting unit of floor elements in the precast-monolithic constructive system ARKOS by means of concrete keys is considered as a prototype of the considered joint. In order to increase a bearing capacity and improve reliability of joints it is envisaged to reinforce keys with space frames. Improvement of joint units is possible to carry out with due account of total number of the factors influencing on strength. Poltava National Technical University named after Yuri Kondratyuk has developed a general methodology for assessment of bearing capacity in keyed joints which is based on the variational method in the theory of concrete plasticity and reflects specificity of stress-strain state of the failure zone. For experimental verification of this methodology investigations have been carried out with the purpose to test operation of keys when they are reinforced in mid-height and reinforcement is distributed in two tiers. The observed experimental fracture pattern in the specimens has confirmed kinematic schemes accepted for calculations and comparative analysis of experimental and theoretical values points to their closeness. Two-level reinforcement significantly improves plastic properties of concrete keys and excludes brittle failure. The proposed design of the joint unit for floor slabs with wall panels is characterized by the ratio of key dimensions and shape of reinforcing cages in the form of hollow cylinders which ensure higher strength and seismic resistance of a joint.Рассмотрена крупнопанельная конструктивная система многоэтажных зданий, индустриальная основа которой создает условия для интенсивного роста объемов домостроения. В качестве плит перекрытий рекомендуется применение многопустотных панелей, что позволяет увеличить расстояние между несущими стенами, улучшить планировочные решения, а также существенно повысить теплои звукозащитные свойства дисков перекрытий (покрытий). Для обеспечения совместной работы плит со стеновыми панелями устраиваются шпоночные стыки, имеющие наибольшее сопротивление действию срезывающих сил. Прототипом рассматриваемого соединения является узел опирания элементов перекрытий сборно-монолитной конструктивной системы «АРКОС» посредством бетонных шпонок. С целью увеличения несущей способности и повышения надежности работы стыков предусматривается армирование шпонок пространственными каркасами. Совершенствование узлов соединений возможно на основе учета полного количества влияющих на прочность факторов. В Полтавском национальном техническом университете имени Юрия Кондратюка разработана общая методика оценивания несущей способности шпоночных соединений, которая базируется на вариационном методе в теории пластичности бетона и отображает специфику напряженно-деформированного состояния зоны разрушения. Для экспериментальной проверки указанной методики выполнено исследование работы шпонок при их армировании посередине высоты и с разнесенной арматурой в два яруса. Наблюдаемая в опытах картина разрушения образцов подтверждает принятые при расчетах кинематические схемы, а сравнительный анализ экспериментальных и теоретических значений предельной нагрузки указывает на их близость. Двухуровневое армирование существенно улучшает пластические свойства бетона шпонок и исключает хрупкое разрушение. Предложенная конструкция узла соединения плит перекрытий со стеновыми панелями отличается соотношением размеров шпонок и формой арматурных каркасов в виде полых цилиндров, которые обеспечивают повышенную прочность и сейсмостойкость стыка

New Functional Materials Based on Nano- and Micro-Objects with Developed Surface

The paper describes the materials with a developed surface fabricated on the basis of electrodeposited copper icosahedral small particles and coatings made of such particles. Increasing the specific surface area of the electrolytic metal is achieved by special heat and/or chemical treatments. Changes in the structure and morphology of icosahedral small particles are analyzed with scanning electron microscopy and X-ray diffraction. The specific surface area of the material is determined with low-temperature gas adsorption technique. Annealing of icosahedral small particles and coatings leads to the formation of the porous structure and a "forest" of whiskers on their surface. Chemical etching of icosahedral small particles corrodes the inside material and provides the formation of hollow particles. Possible applications for obtained materials with a developed surface are offered

EFFECTIVE KEYED CONNECTIONS OF HOLLOW-CORE FLOOR SLABS WITH WALLS IN MODERN LARGE-PANEL HOUSE BUILDING

The paper considers large-panel constructive system of multi-storey buildings and its industrial basis creates conditions for intensive volume growth in house construction. Application of hollow-core panels are recommended as floor slabs that allows to increase a distance between bearing walls, to improve planning solutions, and also significantly to increase thermal and sound protection properties of floor discs (coatings). Keyed joints having the highest resistance to shearing forces are used to ensure joint action of the slabs with wall panels. A supporting unit of floor elements in the precast-monolithic constructive system ARKOS by means of concrete keys is considered as a prototype of the considered joint. In order to increase a bearing capacity and improve reliability of joints it is envisaged to reinforce keys with space frames. Improvement of joint units is possible to carry out with due account of total number of the factors influencing on strength. Poltava National Technical University named after Yuri Kondratyuk has developed a general methodology for assessment of bearing capacity in keyed joints which is based on the variational method in the theory of concrete plasticity and reflects specificity of stress-strain state of the failure zone. For experimental verification of this methodology investigations have been carried out with the purpose to test operation of keys when they are reinforced in mid-height and reinforcement is distributed in two tiers. The observed experimental fracture pattern in the specimens has confirmed kinematic schemes accepted for calculations and comparative analysis of experimental and theoretical values points to their closeness. Two-level reinforcement significantly improves plastic properties of concrete keys and excludes brittle failure. The proposed design of the joint unit for floor slabs with wall panels is characterized by the ratio of key dimensions and shape of reinforcing cages in the form of hollow cylinders which ensure higher strength and seismic resistance of a joint

Computer simulation, analy-sis of force and temperature-speed parameters of the pro-cess of combined machining of Al-Mg-Sc alloys

The results of studies of the combined processing of alloys of the Al-Mg-Sc system with known rheological properties under various temperature-rate and deformation conditions are presented. A computer model of the combined machining process was created and the DEFORM 3D complex was used to analyze the metal flow, the distribution of the strain rate and the temperature of the metal over the cross section of the workpiece when receiving round bars of various diameters. The results of the research were used to develop the production technology of welding wire from alloys of the Al-Mg-Sc system

Computer simulation, analysis of force and temperature-speed parameters of the process of combined machining of Al-Mg-Sc alloys

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.The results of studies of the combined processing of alloys of the Al-Mg-Sc system with known rheological properties under various temperature-rate and deformation conditions are presented. A computer model of the combined machining process was created and the DEFORM 3D complex was used to analyze the metal flow, the distribution of the strain rate and the temperature of the metal over the cross section of the workpiece when receiving round bars of various diameters. The results of the research were used to develop the production technology of welding wire from alloys of the Al-Mg-Sc system

Computer simulation, analysis of force and combined machining of Al-Mg-Sc alloys

The results of studies of the combined processing of alloys of the Al-Mg-Sc system with known rheological properties under various temperature-rate and deformation conditions are presented. A computer model of the combined machining process was created and the DEFORM 3D complex was used to analyze the metal flow, the distribution of the strain rate and the temperature of the metal over the cross section of the workpiece when receiving round bars of various diameters. The results of the research were used to develop the production technology of welding wire from alloys of the Al-Mg-Sc system