The theoretical DFT study of electronic structure of thin Si/SiO2 quantum nanodots and nanowires

The atomic and electronic structure of a set of proposed thin (1.6 nm in diameter) silicon/silica quantum nanodots and nanowires with narrow interface, as well as parent metastable silicon structures (1.2 nm in diameter), was studied in cluster and PBC approaches using B3LYP/6-31G* and PW PP LDA approximations. The total density of states (TDOS) of the smallest quasispherical silicon quantum dot (Si85) corresponds well to the TDOS of the bulk silicon. The elongated silicon nanodots and 1D nanowires demonstrate the metallic nature of the electronic structure. The surface oxidized layer opens the bandgap in the TDOS of the Si/SiO2 species. The top of the valence band and the bottom of conductivity band of the particles are formed by the silicon core derived states. The energy width of the bandgap is determined by the length of the Si/SiO2 clusters and demonstrates inverse dependence upon the size of the nanostructures. The theoretical data describes the size confinement effect in photoluminescence spectra of the silica embedded nanocrystalline silicon with high accuracy.Comment: 22 pages, 5 figures, 1 tabl

Complete intersections and mod p cochains

We give homotopy invariant definitions corresponding to three well known properties of complete intersections, for the ring, the module theory and the endomorphisms of the residue field, and we investigate them for the mod p cochains on a space, showing that suitable versions of the second and third are equivalent and that the first is stronger. We are particularly interested in classifying spaces of groups, and we give a number of examples. This paper follows on from arXiv:0906.4025 which considered the classical case of a commutative ring and arXiv:0906.3247 which considered the case of rational homotopy theory.Comment: To appear in AG

GG-prime and GG-primary GG-ideals on GG-schemes

Let $G$ be a flat finite-type group scheme over a scheme $S$, and $X$ a noetherian $S$-scheme on which $G$-acts. We define and study $G$-prime and $G$-primary $G$-ideals on $X$ and study their basic properties. In particular, we prove the existence of minimal $G$-primary decomposition and the well-definedness of $G$-associated $G$-primes. We also prove a generalization of Matijevic-Roberts type theorem. In particular, we prove Matijevic-Roberts type theorem on graded rings for $F$-regular and $F$-rational properties.Comment: 54pages, added Example 6.16 and the reference [8]. The final versio

Class and rank of differential modules

A differential module is a module equipped with a square-zero endomorphism. This structure underpins complexes of modules over rings, as well as differential graded modules over graded rings. We establish lower bounds on the class--a substitute for the length of a free complex--and on the rank of a differential module in terms of invariants of its homology. These results specialize to basic theorems in commutative algebra and algebraic topology. One instance is a common generalization of the equicharacteristic case of the New Intersection Theorem of Hochster, Peskine, P. Roberts, and Szpiro, concerning complexes over noetherian commutative rings, and of a theorem of G. Carlsson on differential graded modules over graded polynomial rings.Comment: 27 pages. Minor changes; mainly stylistic. To appear in Inventiones Mathematica

Prospects of Spin Catalysis on Spin-Polarized Graphene Heterostructures

Extreme points on potential energy surfaces of Ni adatom on free-standing graphene and top:fcc and hcp:fcc graphene/ Ni(111) heterostructures in different spin states were studied using periodic boundary conditions density functional theory approach. It was found that the spin states of the substrates strongly influence the energy of the Ni adatom extreme points on potential energy surface by decreasing (top:fcc heterostructure) or increasing (hcp:fcc heterostructure) the total energies of Z1, Z1 , and Z2 Ni adatom coordinations on graphene. This phenomenon offers unique possibilities to control the potential energy surfaces of transition metal adatoms and promote surface chemical reactions using induced spin polarization of graphene substrates

Support varieties for selfinjective algebras

Support varieties for any finite dimensional algebra over a field were introduced by Snashall-Solberg using graded subalgebras of the Hochschild cohomology. We mainly study these varieties for selfinjective algebras under appropriate finite generation hypotheses. Then many of the standard results from the theory of support varieties for finite groups generalize to this situation. In particular, the complexity of the module equals the dimension of its corresponding variety, all closed homogeneous varieties occur as the variety of some module, the variety of an indecomposable module is connected, periodic modules are lines and for symmetric algebras a generalization of Webb's theorem is true

Stretched exponential relaxation in a diffusive lattice model

We studied the single dimer dynamics in a lattice diffusive model as a function of particle density in the high densification regime. The mean square displacement is found to be subdiffusive both in one and two dimensions. The spatial dependence of the self part of the van Hove correlation function displays as function of $r$ a single peak and signals a dramatic slow down of the system for high density. The self intermediate scattering function is fitted to the Kohlrausch-Williams-Watts law. The exponent $\beta$ extracted from the fits is density independent while the relaxation time $\tau$ follows a scaling law with an exponent 2.5.Comment: 5 pages, 3 figures, to be published in Phys. Rev.

EPIDEMIOLOGICAL, CLINICA.L AND VIROLOGICAL STUDIES ON INFLUENZA MORBIDITY RATES FOR ТНЕ PERIOD APRIL 1962 – МАY 1963 IN ТНЕ СIТУ OF VARNA

Тhe epidemic process of influenza acquires vaгious forms in its couгse: pandemics, epidemics аnd sporadic morbidity inbetween epidemics. Wе dispose of mоrе precise data оn its course in Bulgaria since 1952. Мorе scanty аrе the data which characteгize influenza epidemics in the city of Vагnа up to 1955 which is seen on Diagr. 1. From the latter it becomes evident that influenza morbidity rates in the city of Vагnа run parallel to morbidity rates in the whole country, being occasionally morе intensive - 1959, 1962. Тlie diаgrаm reveals high level for influenza morbldity rates fог the countгy and the city of Vаrnа in 1956 and аn epidemic peak in 1957, 1959 аnd 1962. Тhe epidemic peak in 1962 is due to аn influenza outbreak caused bу virus А2 which started at the end of January and continued till Магсh, the same уеаr.After the epidemics а period was established, characteгized bу а low level of influenza morbldity rates in the city of Varna. Stress should bе laid оn the fact that determination of actual levels of influenza morbidity rates inbetween epidemics is particularly difficult owing to the imperfect diagnosis and the diversity of clinical forms of influenza

Content of Metals in Phragmites australis Trin. ex Steud and Potamogeton pectinatus L. from Water Bodies of Different Salinity

Металлы определяли в двух видах макрофитов – Phragmites australis Trin. ex Steud и Potamogeton pectinatus L., произрастающих в водоемах с разной соленостью, с помощью эмиссионного спектрометра с индуктивно-связанной плазмой. Анализ результатов методом главных компонент показал, что на валовое содержание металлов влияет вид макрофитов и условия окружающей среды, в частности химический состав воды. Оба вида макрофитов из пресноводного водохранилища Бугач отличались более высокими концентрациями железа, алюминия, никеля, ванадия и кобальта по сравнению с теми же видами макрофитов, собранными в солоноватоводных озерах. Однако для макрофитов из оз. Шира, отобранных в опресненной и солоноватоводной частях озера, расхождений в содержании данных металлов не выявлено. В ряде случаев пробы из одной точки, но собранные в разные годы имели существенные различия – это наблюдалось для растений тростника из солоноватоводной станции оз. Шира, и растений рдеста из оз. Шунет. Было установлено, что наиболее высокое валовое содержание большинства металлов характерно для P. pectinatusMetals were determined in two species of macrophytes Phragmites australis Trin. ex Steud and Potamogeton pectinatus L. grown in lakes of different salinity, using emission spectrometer with inductively coupled plasma. Principal component analysis revealed that the total metal content is influenced by species of macrophytes and environmental conditions (in particular water chemistry). Both species of macrophytes from freshwater reservoir Bugach were characterized by higher concentrations of Fe, Al, Ni, V and Co in comparison with the same species from brackish lakes. However, there were no significant differences in content of these metals between samples of macrophytes taken in desalinated and saltwater parts of Shira Lake. In some cases, metal content of samples collected in different years at the same place were significantly different. It was observed for plants of Ph. australis collected in brackish station of Shira Lake, and plants of P. pectinatus from Lake Shunet. It was found that the highest total content of most metals is typical for P. pectinatu