SIMULATION OF PHASE STATE AND OF THERMODYNAMICAL PROPERTIES OF NATURAL MULTICOMPONENT SYSTEMS AT DESIGNING OF EXPLOITATION AND OF USE OF OIL DEPOSITS AND OF GAS DEPOSITS

There the study purpose is to create the common methodological basis of computation of phase state and of properties of natural hydrocarbon mixes for the comprehensive simulation of exploitation process and of use process of oil deposits and of gas deposits. The new computation method of steam-and-fluid equlibrium, of thermal and caloric properties of natural gases and of natural oils, the simulation method of differential condensation of multicomponent systems in the accurate definition have been developed. The problems of multicomponent filtration with regard to the mass exchange between the phases have been solved. The comprehensive approach to the mathematical simulation of differential condensation of natural gases and of differential degassing of pool oils, of multicomponent filtration, of motion of mix to be produced in the well, of field separation has been realized. The simulators for the estimate of process indicators of exploitation of beds with the application of gas methods for the rise of oil yield and of condensate yield have been developed. The software package, which was made on the basis of developed methods and of mathematical simulators, has been used in the oil-and-gas producing industry and in the geological surveying industryAvailable from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio

Preface to Special issue on User Modeling for Web information retrieval

The new innovative tools mainly user modeling and adaptive personalization required for information retrieval systems on the web was discussed. The importance and role of user modeling and adaptive personalization were identified to be capable of comprehending specific user information needs and to effectively filter out irrelevant information. New algorithms were also needed for adaptive personalization based on techniques such as machine learning natural language processing and new paradigms for interaction and navigation. The future information tools would offer better ways to deal with the information overload by blending multiple ways of information access with adaptation to individual needs and interests

Temperature-Dependent Recombination Processes in Small-Sized PbSe/PbS Core/Shell Colloidal Quantum Dots

The work focuses on the optical investigation of temperature-dependent recombination processes in small-sized PbSe/PbS core/shell colloidal quantum dots (CQDs) with core diameter of (2 – 2.5) nm and the shell thickness of (0.5 – 1.0) nm under air-free conditions and after air exposure. These CQDs have a tunable absorption edge around 1 μm and a rather narrow photoluminescence linewidth, their emission recombination process is characterized by the μs time-scale and by longer radiative lifetimes in the entire temperature range and especially at low temperatures (a 2.6-fold increase) as compared to the corresponding PbSe samples. The PbSe/PbS core/shell CQDs are oxidation-stable towards time-limited air exposure. <p>DOI: <a href="http://dx.doi.org/10.5755/j01.ms.20.2.6321">http://dx.doi.org/10.5755/j01.ms.20.2.6321</a></p

Comprehensive Route to the Formation of Alloy Interface in Core/Shell Colloidal Quantum Dots

The electronic properties of colloidal quantum dots (CQDs) have shown intriguing potential in recent years for implementation in various optoelectronic applications. However, their chemical and photochemical stabilities, mainly derived from surface properties, have remained a major concern. This paper reports a new strategic route for the synthesis of surface-treated CQDs, the CdSe/CdS core/shell heterostructures, based on low-temperature coating of a shell constituent, followed by a programmed annealing process. A comprehensive follow-up of the stability and the optical properties through the various synthesis stages is reported, suggesting that the low-temperature coating is responsible for the formation of a sharp interface between the core and the shell, whereas a postcoating annealing process leads to the generation of a thin alloy interfacial layer. At the end of the process, the CdSe/CdS CQDs show a significant improvement of the photoluminescence quantum yield, as well as an exceptional photostability. Consequently, the work reported here provides a convenient generic route to the formation of core/shell CQDs to be employed as a procedure for achieving various other heterostructures

Influence of Alloying on the Optical Properties of IV–VI Nanorods

The synthesis and structural and optical characterization of PbSe_<i>x</i>S_1–<i>x</i> and PbSe/PbSe_<i>x</i>S_1–<i>x</i> nanorods with a diameter between 2 and 4.5 nm and a length of 10 to 38 nm is reported. The energy band gap of the nanorods exhibits a pronounced variation upon the change in diameter and composition, with a minor influence on lengths beyond 10 nm. The photoluminescence spectrum of the nanorods is composed of a dominant band, accompanied by a satellite band at elevated temperatures. The dominant band shows an exceptionally small band gap temperature coefficient and negligible extension of the radiative lifetime at cryogenic temperatures compared with the photoluminescence processes in PbSe nanorods and in PbSe_<i>x</i>S_1–<i>x</i> quantum dots with similar band gap energy. A theoretical model suggests the occurrence of independent transitions from a pair of band-edge valleys, located at the L points of Brillouin zone, related to the dominant and satellite emission processes. Each valley is four-fold degenerate and possesses a relatively small electron–hole exchange interaction