We present first-principles approaches based on density functional theory for calculating positron states and annihilation characteristics in condensed matter. The treatment of the electron-positron correlation effects (the enhancement of the electron density at the positron with respect to mean-field density) is shown to play a crucial role when calculating the annihilation rates. A generalize...

The presence of dark matter in the halo of our galaxy could be revealed through indirect detection of annihilation products. Dark matter annihilation is one of the possible interpretations of the recent measured excesses in positron and electron fluxes, once boost factors of the order of 10 or more are taken into account. Such boost factors are actually achievable through the velocity-dependent...

We develop general expressions for the raising and lowering operators that belong to the orthogonal polynomials of hypergeometric type with discrete and continuous variable. We construct the creation and annihilation operators that correspond to the normalized polynomials and study their algebraic properties in the case of the Kravchuk/Hermite Meixner/Laguerre polynomials. 1. Introduction. In a...

nowadays, tube bonding in vehicles structure is noticeably considered by many researches. in this paper, local tube compression process by a rubber ring has been studied. firstly, simulation of the process was performed by fem. then, experimental test has been carried out to validate the numerical results. numerical and experimental results were compared showing a good agreement. in the second ...

The restricted solid-on-solid models in the anti-ferromagnetic regime is studied in the framework of quantum affine algebras. Following the line developed recently for vertex models, a representation theoretical picture is presented for the structure of the space of states. The local operators and the creation/annihilation operators of quasi-particles are defined using vertex operators, and the...

a set $s$ of vertices in a graph $g$ is a dominating set if every vertex of $v-s$ is adjacent to some vertex in $s$. the domination number $gamma(g)$ is the minimum cardinality of a dominating set in $g$. the annihilation number $a(g)$ is the largest integer $k$ such that the sum of the first $k$ terms of the non-decreasing degree sequence of $g$ is at most the number of edges in $g$. in this p...

Abstract Positron Annihilation Spectroscopy (PAS) is a non-destructive technique used mostly in material science for studying open spaces/free volumes materials. In this work, several different nuclear materials originating from the fuel cycle or round-robin exercises are analyzed by PAS. Our goal was, as first test of applicability, to check whether potentially suitable forensic examination or...

We have measured the momentum distribution of the electron-positron annihilating pair in diamond as a function of crystallographic orientation, using the Doppler broadening technique of positron annihilation spectroscopy. A 1% variation in the longitudinal projection of the momentum distribution was observed as the sample was rotated about the (110) axis. This anisotropic distribution shows an ...