Search results for "MEG"

Prediction of compound channel secondary flows using anisotropic turbulence models

2014

Hyperfine interaction in the Autler-Townes effect: The formation of bright, dark, and chameleon states

2017

This paper is devoted to clarifying the implications of hyperfine (HF) interaction in the formation of adiabatic (i.e., ``laser-dressed'') states and their expression in the Autler-Townes (AT) spectra. We first use the Morris-Shore model [J. R. Morris and B. W. Shore, Phys. Rev. A 27, 906 (1983)] to illustrate how bright and dark states are formed in a simple reference system where closely spaced energy levels are coupled to a single state with a strong laser field with the respective Rabi frequency ${\mathrm{\ensuremath{\Omega}}}_{S}$. We then expand the simulations to realistic hyperfine level systems in Na atoms for a more general case when non-negligible HF interaction can be treated as…

The MEGA project

2004

Abstract We describe the development of a new telescope for Medium Energy Gamma-Ray Astronomy (MEGA) for the energy band 0.4–50 MeV. As a successor to COMPTEL and EGRET (low energies), MEGA aims to improve the sensitivity for astronomical sources by at least an order of magnitude. It could thus fill the severe sensitivity gap between scheduled or operating hard-X-ray and high-energy γ-ray missions and open the way for a future Advanced Compton Telescope. MEGA records and images γ-rays by completely tracking Compton and Pair creation events in a stack of double sided Si-strip track detectors surrounded by a pixelated CsI calorimeter. A scaled down prototype has been built and calibrations us…

Approximation of the Maxwell equations in anisotropic inhomogeneous media

1996

Let Ω ∈ L be in ℝ 2. We consider the initial-boundary value problem $$ \begin{array}{l}rot\,E\left( {x,t} \right) + \mu \left( x \right)\frac{\partial }{{\partial t}}H\left( {x,t} \right) = J\left( {x,t} \right), \\\left( {x,t} \right) \in \Omega \, \times \,(0,T], \\curl\,H\left( {x,t} \right) - \varepsilon \left( {\frac{\partial }{{\partial t}}} \right)E\left( {x,t} \right) = k\left( {x,t} \right), \\n \wedge E\left( {x,t} \right) = 0, \\\left( {x,t} \right) \in \partial \Omega \, \times \,(0,T], \\\left( {E\left( {x,0} \right),H\left( {x,0} \right)} \right) = \left( {{E_0}\left( x \right),\,{H_0}\left( x \right)} \right), \\x \in \bar \Omega \\\end{array} $$ (13.1) .

Nonlinear anisotropic heat conduction in a transformer magnetic core

1996

In this chapter we deal with a quasilinear elliptic problem whose classical formulation reads: Find \( u \in {C^1}\left( {\bar \Omega } \right) \) such that u|Ω ∈ C 2(Ω) and $$ - div\left( {A\left( { \cdot ,u} \right)grad\;u} \right) = f\quad in\;\Omega $$ (9.1) $$ u = \bar u\quad on\;{\Gamma _1} $$ (9.2) $$ \alpha u + {n^T}A\left( { \cdot ,u} \right)grad\;u = g\quad on\;{\Gamma _2} $$ (9.3) where Ω ∈ L, n = (n 1, ..., n d ) T is the outward unit normal to ∂Ω, d ∈ {1, 2, ...,}, Γ1 and Γ2 are relatively open sets in the boundary ∂Ω, \({\overline \Gamma _1} \cup {\overline \Gamma _2} = \partial \Omega ,\,{\Gamma _1} \cap {\Gamma _2} = \phi\), \( A = \left( {{a_{ij}}} \right)_{i,j = 1}^d \) is…

Coulomb blockade in one-dimensional arrays of high-conductance tunnel junctions

2000

Properties of one-dimensional (1D) arrays of low Ohmic tunnel junctions (i.e. junctions with resistances comparable to, or less than, the quantum resistance $R_{\rm q}\equiv h/e^2\approx 25.8$ k$\Omega$) have been studied experimentally and theoretically. Our experimental data demonstrate that -- in agreement with previous results on single- and double-junction systems -- Coulomb blockade effects survive even in the strong tunneling regime and are still clearly visible for junction resistances as low as 1 k$\Omega$. We have developed a quasiclassical theory of electron transport in junction arrays in the strong tunneling regime. Good agreement between the predictions of this theory and the …

Phenomenological description of counterflow superfluid turbulence in rotating containers

2004

In this paper a simple equation for the vortex line density describing some of the most relevant observed effects in counterflow superfluid turbulence in ${}^{4}\mathrm{He}$ in the presence of rotation is proposed. This model is based on a generalization of Vinen's equation which incorporates as additional quantity the angular velocity \ensuremath{\Omega}.

Harmonic Vibrational Excitations in Disordered Solids and the "Boson Peak"

1998

We consider a system of coupled classical harmonic oscillators with spatially fluctuating nearest-neighbor force constants on a simple cubic lattice. The model is solved both by numerically diagonalizing the Hamiltonian and by applying the single-bond coherent potential approximation. The results for the density of states $g(\omega)$ are in excellent agreement with each other. As the degree of disorder is increased the system becomes unstable due to the presence of negative force constants. If the system is near the borderline of stability a low-frequency peak appears in the reduced density of states $g(\omega)/\omega^2$ as a precursor of the instability. We argue that this peak is the anal…

Momentum structure of the self-energy and its parametrization for the two-dimensional Hubbard model

2016

We compute the self-energy for the half-filled Hubbard model on a square lattice using lattice quantum Monte Carlo simulations and the dynamical vertex approximation. The self-energy is strongly momentum dependent, but it can be parametrized via the non-interacting energy-momentum dispersion $\varepsilon_{\mathbf{k}}$, except for pseudogap features right at the Fermi edge. That is, it can be written as $\Sigma(\varepsilon_{\mathbf{k}},\omega)$, with two energy-like parameters ($\varepsilon$, $\omega$) instead of three ($k_x$, $k_y$ and $\omega$). The self-energy has two rather broad and weakly dispersing high energy features and a sharp $\omega= \varepsilon_{\mathbf{k}}$ feature at high tem…

Microscopic dynamics of molecular liquids and glasses: Role of orientations and translation-rotation coupling

2001

We investigate the dynamics of a fluid of dipolar hard spheres in its liquid and glassy phase, with emphasis on the microscopic time or frequency regime. This system shows rather different glass transition scenarios related to its rich equilibrium behavior which ranges from a simple hard sphere fluid to a long range ferroelectric orientational order. In the liquid phase close to the ideal glass transition line and in the glassy regime a medium range orientational order occurs leading to a softening of an orientational mode. To investigate the role of this mode we use the molecular mode-coupling equations to calculate the spectra $\phi_{lm}^{\prime \prime}(q,\omega)$ and $\chi _{lm}''(q,\ome…