176 research outputs found
Cumulant approach to weakly doped antiferromagnets
We present a new approach to static and dynamical properties of holes and
spins in weakly doped antiferromagnets in two dimensions. The calculations are
based on a recently introduced cumulant approach to ground--state properties of
correlated electronic systems. The present method allows to evaluate hole and
spin--wave dispersion relations by considering hole or spin excitations of the
ground state. Usually, these dispersions are found from time--dependent
correlation functions. To demonstrate the ability of the approach we first
derive the dispersion relation for the lowest single hole excitation at
half--filling. However, the main purpose of this paper is to focus on the
mutual influence of mobile holes and spin waves in the weakly doped system. It
is shown that low-energy spin excitations strongly admix to the ground--state.
The coupling of spin waves and holes leads to a strong suppression of the
staggered magnetization which can not be explained by a simple rigid--band
picture for the hole quasiparticles. Also the experimentally observed doping
dependence of the spin--wave excitation energies can be understood within our
formalism.Comment: REVTEX, 25 pages, 7 figures (EPS), to be published in Phys. Rev.
Electronic Structure and Valence Band Spectra of Bi4Ti3O12
The x-ray photoelectron valence band spectrum and x-ray emission valence-band
spectra (Ti K _beta_5, Ti L_alpha, O K_alpha) of Bi4Ti3O12 are presented
(analyzed in the common energy scale) and interpreted on the basis of a
band-structure calculation for an idealized I4/mmm structure of this material.Comment: 6 pages + 7 PostScript figures, RevTex3.0, to be published in
Phys.Rev.B52 (Oct.95). Figures also available via anonymous ftp at
ftp://ftp.physik.uni-osnabrueck.de/pub/apostnik/BiTiO
Religious Identity, Religious Attendance, and Parental Control
Using a national sample of adolescents aged 10–18 years and their parents (N = 5,117), this article examines whether parental religious identity and religious participation are associated with the ways in which parents control their children. We hypothesize that both religious orthodoxy and weekly religious attendance are related to heightened levels of three elements of parental control: monitoring activities, normative regulations, and network closure. Results indicate that an orthodox religious identity for Catholic and Protestant parents and higher levels of religious attendance for parents as a whole are associated with increases in monitoring activities and normative regulations of American adolescents
Mandibular Actinomyces osteomyelitis complicating florid cemento-osseous dysplasia: case report
Influence of maternal denomination, God concepts and child-rearing practices on young children's God concepts
Thermal conductivity of high- T c superconductors
This paper reviews existing data on the thermal conductivity of high- T c superconductors. Included are discussions of pristine polycrystalline high- T c ceramics, single crystal specimens, and high- T c materials structurally modified by substitution or by radiation damage. The thermal conductivity of high- T c superconductors is compared with that of conventional superconductors, and dramatic differences are found between the two families. Mechanisms of thermal conductivity applicable to high- T c perovskites are discussed and implications for theories of high- T c superconductivity are noted.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45121/1/10948_2004_Article_BF00617463.pd
Możliwości wytwarzania kompozytowych warstw powierzchniowych wzmacnianych twardymi cząstkami ceramicznymi przy użyciu napawania laserowego
The paper presents research results of metal matrix composite coatings produced on S355 steel using laser cladding. Two powder mixtures Stellite-6/30% B4C and Stellite-6/30% SiC were used. The aim of this study was to determine the applicability of these materials in the production of composite coatings having a microstructure similar to sintered carbides. Applied carbides were characterized by very high hardness (B4C -3800 HV, SiC -2500 HV) and a high melting point (B4C -2763°C, SiO -2730°C).Such parameters are conducive to formation of coatings with composite microstructure. The purpose of analyzed process consisted in complete melting of matrix material, partial melting of reinforcing particles and minimal melting of substrate material. This effect has been achieved to a limited extent.Przedstawiono wyniki badań kompozytowych warstw powierzchniowych wytwarzanych na stali S355przy użyciu proszkowego napawania laserowego. Zastosowano dwie mieszaniny proszkowe Stellite-6/30%B4C oraz Stellite-6/30%SiC.Celem badań było określenie możliwości zastosowania tego rodzaju materiałów do wytwarzania kompozytowych warstw powierzchniowych o mikrostrukturze zbliżonej do węglików spiekanych. Zastosowane węgliki charakteryzowały się bardzo dużą twardością (B4C -3800 HV, SiC -2500 HV) oraz wysoką temperaturą topnienia (B4C -2763°C, SiC -2730°C). Takie parametry sprzyjają wytworzeniu warstwy o budowie kompozytowej. Celem badanego w pracy procesu było całkowite przetopienie materiału osnowy, częściowe cząstek fazy wzmacniającej oraz minimalne materiału podłoża. Efekt ten został osiągnięty w ograniczonym zakresie
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