Метод трехмерной триангуляции в задачах кластерного анализа

Представлен метод многомерного шкалирования на основе трехмерной триангуляции. Рассмотрена возможность качественного сохранения геометрической структуры множества объектов при отображении многомерного пространства в трехмерное. Приведены результаты применения метода для решения задачи кластеризации на примере периодической системы элементов Д.И. Менделеева. Экспериментально показано, что по критериям качества кластеризации предложенный метод более эффективен в сравнении с методами k-средних и нейронной сети Кохонена.Представлено метод багатовимірного шкалювання на основі тривимірної тріангуляції. Розглянуто можливість якісного збереження геометричної структури множини об’єктів при відображенні багатовимірного простору в тривимірне. Наведено результати застосування методу для вирішення задачі кластеризації на прикладі періодичної системи елементів Д.І. Менделєєва. Експериментально показано, що за критеріями якості кластеризації запропонований метод більш ефективний у порівнянні з методами k-середніх та нейронної мережі Кохонена.The method of multidimensional scaling on the basis of the 3-D triangulation is presented. The qualitative preservation possibility of geometrical structure of objects by multidimensional space mapping to three- dimensional space is considered. The results of application of the method for clustering problem of the Mendeleyev periodic table are presented. It is experimentally shown, that the presented method is more effective by criteria of clustering quality in comparison with the methods of k-averages and the Kohonen neural network

Near-infrared Emitting CulnSe2/CulnS2 Dot Core/Rod Shell Heteronanorods by Sequential Cation Exchange

The direct synthesis of heteronanocrystals (HNCs) combining different ternary semiconductors is challenging and has not yet been successful. Here, we report a sequential topotactic cation exchange (CE) pathway that yields CuInSe2/CuInS2 dot core/rod shell nanorods with near-infrared luminescence. In our approach, the Cu+ extraction rate is coupled to the In3+ incorporation rate by the use of a stoichiometric trioctylphosphine-InCl3 complex, which fulfills the roles of both In-source and Cu-extracting agent. In this way, Cu+ ions can be extracted by trioctylphosphine ligands only when the In–P bond is broken. This results in readily available In3+ ions at the same surface site from which the Cu+ is extracted, making the process a direct place exchange reaction and shifting the overall energy balance in favor of the CE. Consequently, controlled cation exchange can occur even in large and anisotropic heterostructured nanocrystals with preservation of the size, shape, and heterostructuring of the template NCs into the product NCs. The cation exchange is self-limited, stopping when the ternary core/shell CuInSe2/CuInS2 composition is reached. The method is very versatile, successfully yielding a variety of luminescent CuInX2 (X = S, Se, and Te) quantum dots, nanorods, and HNCs, by using Cd-chalcogenide NCs and HNCs as templates. The approach reported here thus opens up routes toward materials with unprecedented properties, which would otherwise remain inaccessible

Dynamical nuclear polarization by means of shallow donors in ZnO quantum dots

The almost complete dynamic nuclear polarization (DNP) of nuclear spins has been demonstrated can be achieved in ZnO and AgCl single crystals by saturating the EPR transition of the shallow donor (SD) present in this crystals with using high-frequency (275 and 95 GHz) at low temperatures. DNP effects have also been observed in ZnO quantum dots (QD's) where polarization of 67Zn nuclear spins in ZnO core and of 1H nuclear spins in the Zn(OH)2 capping layer have been obtained by saturating the EPR transition of the SD present in the ZnO QD's. DNP manifests itself via a shift of the EPR lines of SD in bulk ZnO and AgCl crystals and the creation of a hole and an antihole in the EPR absorption line of the SD in QD's. The enhancement of the nuclear polarization opens the possibility to study semiconductor nanostructures with NMR techniques. © 2009 Elsevier B.V. All rights reserved

Зимостойкость некоторых видов рода Sorbus L. в Донбассе

Изучены анатомические особенности годичных побегов Sorbus persica Hedl., S. domestica L. и S. aucuparia L. Определены толщина тканей и степень лигнификации ксилемы. Наиболее развиты покровные и механические ткани у S. aucuparia, годичные побеги полностью вызревшие. У S. persica наблюдается отставание в развитии тканей и степени одревеснения побегов по сравнению с S. aucuparia. Отмечена высокая зимостойкость S. domestica и S. aucuparia и более низкая – S. persica. К перспективным видам отнесены S. domestica и S. aucuparia. Вид – S. persica нецелесообразно вводить в ассортимент декоративных растений юго-востока Украины.The anatomical peculiarities of annual spears of Sorbus persica Hedl., S. domestica L. and S. aucuparia L. were studied. The tissue depth and xylem lignification rate were defined. The tissues of S. aucuparia are most developed and annual spears are fully mature for vegetative period. S. persica lags in terms of tissue development and spear lignification rate compared to S. aucuparia. S. domestica and S. aucuparia revealed winter resistance at high level, whereas S. persica demonstrated it at low level. S. domestica and S. aucuparia are treated as perspective, while S. persica is unreasonable for introduction to the assortment of decorative plants of south-east of Ukraine

Evidence of exchange interaction of localized carriers and transition metals in diluted II-VI nanostructures: ODMR study

Copyright © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimOptically detected magnetic resonance study of (CdMn)Te/(CdMg)Te quantum wells allowed to reveal the formation of exchange-coupled complexes consisting of Mn ions and localized holes in quantum wells with excess hole concentration and the directional electron tunneling towards wider wells in multiple quantum well structures. The existence of a distribution of Mn-hole complexes that differ in a number of Mn ions interacting with a localized hole is justified. In colloidal cobalt doped ZnO nanocrystals, several nm in diameter, the interaction between the magnetic ions and the shallow donor electron in the confined system of ZnO quantum dots has been revealed. Direct evidence of interaction of Co ions with the interstitial Li shallow donor in the ZnO nanocrystal core and hyperfine coupling with 1H in the quantum dot shell have been demonstrated. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Evidence of exchange interaction of localized carriers and transition metals in diluted II-VI nanostructures: ODMR study

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Optically detected magnetic resonance study of (CdMn)Te/(CdMg)Te quantum wells allowed to reveal the formation of exchange-coupled complexes consisting of Mn ions and localized holes in quantum wells with excess hole concentration and the directional electron tunneling towards wider wells in multiple quantum well structures. The existence of a distribution of Mn-hole complexes that differ in a number of Mn ions interacting with a localized hole is justified. In colloidal cobalt doped ZnO nanocrystals, several nm in diameter, the interaction between the magnetic ions and the shallow donor electron in the confined system of ZnO quantum dots has been revealed. Direct evidence of interaction of Co ions with the interstitial Li shallow donor in the ZnO nanocrystal core and hyperfine coupling with 1H in the quantum dot shell have been demonstrated

Exciton-phonon coupling in InP quantum dots with ZnS and (Zn, Cd) Se shells

InP-based colloidal quantum dots are promising for optoelectronic devices such as light-emitting diodes and lasers. Understanding and optimizing their emission process is of scientific interest and essential for large-scale applications. Here we present a study of the exciton recombination dynamics in InP QDs with various shells: ZnS, ZnSe, and (Zn,Cd)Se with different amounts of Cd (5, 9, 12%). Phonon energies extracted from Raman spectroscopy measurements at cryogenic temperatures (4-5 K) are compared with exciton emission peaks observed in fluorescence line narrowing spectra. This allowed us to determine the position of both the bright F = +/- 1 state and the lowest dark F = +/- 2 state. We could identify the phonon modes involved in the radiative recombination of the dark state and found that acoustic and optical phonons of both the core and the shell are involved in this process. The Cd content in the shell increases electron wave-function delocalization, and thereby enhances the exciton-phonon coupling through the Frohlich interaction

Analysis of the 1 Year Outdoor Performance of Quantum Dot Luminescent Solar Concentrators

Three quantum dot luminescent solar concentrators (QDLSCs) are constructed to assess their performance in an outdoor environment over an entire year. The QDLSCs have a (Formula presented.) PMMA-Kraton-PMMA sandwich structure with either InP/ZnSe/ZnS, (Formula presented.), or CdSe/CdS/ZnS core/shell quantum dots incorporated in the Kraton interlayer. Furthermore, two reference LSCs are included: one using Lumogen F Red 305 as the luminophore and one without a luminophore in the Kraton layer. The power conversion efficiency is assessed for a cloudy and a sunny day, showing the influence of diffuse and direct irradiance. Moreover, the influence of mounting orientation and direct irradiance is analyzed for individual solar strips attached to the sides. Long-term results show an efficiency increase of (Formula presented.) and InP/ZnSe/ZnS QDLSC while the CdSe/CdS/ZnS QDLSCs and the Lumogen LSC show a pronounced drop in efficiency in the first 3 months. Photodegradation studies under continuous white light exposure for 420 h are performed on smaller pieces cut from the QDLSCs before their assembly outdoors and show similar trends to those observed in the 1 year outdoor study. Future research will focus on the postmortem analysis of the QDLSCs and increasing the efficiencies

Synthesis of Monodisperse Nanocrystals via Microreaction: Open-to-Air Synthesis with Oleylamine as a Coligand

Microreaction provides a controllable tool to synthesize CdSe nanocrystals (NCs) in an accelerated fashion. However, the surface traps created during the fast growth usually result in low photoluminescence (PL) efficiency for the formed products. Herein, the reproducible synthesis of highly luminescent CdSe NCs directly in open air was reported, with a microreactor as the controllable reaction tool. Spectra investigation elucidated that applying OLA both in Se and Cd stock solutions could advantageously promote the diffusion between the two precursors, resulting in narrow full-width-at-half maximum (FWHM) of PL (26 nm). Meanwhile, the addition of OLA in the source solution was demonstrated helpful to improve the reactivity of Cd monomer. In this case, the focus of size distribution was accomplished during the early reaction stage. Furthermore, if the volume percentage (vol.%) of OLA in the precursors exceeded a threshold of 37.5%, the resulted CdSe NCs demonstrated long-term fixing of size distribution up to 300 s. The observed phenomena facilitated the preparation of a size series of monodisperse CdSe NCs merely by the variation of residence time. With the volume percentage of OLA as 37.5% in the source solution, a 78 nm tuning of PL spectra (from 507 to 585) was obtained through the variation of residence time from 2 s to 160 s, while maintaining narrow FMWH of PL (26–31 nm) and high QY of PL (35–55%)

In Situ Optical and X-ray Spectroscopy Reveals Evolution toward Mature CdSe Nanoplatelets by Synergetic Action of Myristate and Acetate Ligands

The growth of two-dimensional platelets of the CdX family (X = S, Se, or Te) in an organic solvent requires the presence of both long- and short-chain ligands. This results in nanoplatelets of atomically precise thickness and long-chain ligand-stabilized Cd top and bottom surfaces. The platelets show a bright and spectrally pure luminescence. Despite the enormous interest in CdX platelets for optoelectronics, the growth mechanism is not fully understood. Riedinger et al. studied the reaction without a solvent and showed the favorable role for short-chain carboxylates for growth in two dimensions. Their model, based on the total energy of island nucleation, shows favored side facet growth versus growth on the top and bottom surfaces. However, several aspects of the synthesis under realistic conditions are not yet understood: Why are both short- and long-chain ligands required to obtain platelets? Why does the synthesis result in both isotropic nanocrystals and platelets? At which stage of the reaction is there bifurcation between isotropic and 2D growth? Here, we report an in situ study of the CdSe nanoplatelet reaction under practical synthesis conditions. We show that without short-chain ligands, both isotropic and mini-nanoplatelets form in the early stage of the process. However, most remaining precursors are consumed in isotropic growth. Addition of acetate induces a dramatic shift toward nearly exclusive 2D growth of already existing mini-nanoplatelets. Hence, although myristate stabilizes mini-nanoplatelets, mature nanoplatelets only grow by a subtle interplay between myristate and acetate, the latter catalyzes fast lateral growth of the side facets of the mini-nanoplatelets