Search results for "Sip"
showing 10 items of 1280 documents
Maximum Lifetime of the Wireless Sensor Network and the Gossip Problem
2018
In the gossip problem each node of the graph G possesses a unique piece of information - the gossip message. A sequence of one-way or two-way communications between pair of nodes is made to spread the messages so that any node of the graph knows all the gossips. The question is, what is the minimum number of calls between pairs of nodes needed to exchange all gossip messages? The solution to the two-way communication gossip problem is that \(2N-4\) calls (\(N\ge 4\)) suffice if and only if the graph contains a four cycle subgraph. For one-way communication problem the classical results states that in a strongly connected graph \(2N-2\) calls (\(N\ge 4\)) suffice. In this paper we consider t…
Realistic investigations of correlated electron systems with LDA + DMFT
2006
Conventional band structure calculations in the local density approximation (LDA) [1–3] are highly successful for many materials, but miss important aspects of the physics and energetics of strongly correlated electron systems, such as transition metal oxides and f-electron systems displaying, e.g., Mott insulating and heavy quasiparticle behavior. In this respect, the LDA + DMFT approach which merges LDA with a modern many-body approach, the dynamical mean-field theory (DMFT), has proved to be a breakthrough for the realistic modeling of correlated materials. Depending on the strength of the electronic correlation, a LDA + DMFT calculation yields the weakly correlated LDA results, a strong…
Roton-roton crossover in strongly correlated dipolar Bose-nonstnon condensates
2011
We study the pair correlations and excitations of a dipolar Bose gas layer. The anisotropy of the dipole-dipole interaction allows us to tune the strength of pair correlations from strong to weak perpendicular and weak to strong parallel to the layer by increasing the perpendicular trap frequency. This change is accompanied by a roton-roton crossover in the spectrum of collective excitations, from a roton caused by the head-to-tail attraction of dipoles to a roton caused by the side-by-side repulsion, while there is no roton excitation for intermediate trap frequencies. We discuss the nature of these two kinds of rotons and the relation to instabilities of dipolar Bose gases. In both regime…
Fermion Condensation in Finite Systems
2014
Here we consider another example of systems, in which fermion condensation takes place. These are what is called finite Fermi systems, i.e. systems with finite number of fermions, contrary to a solid, where the number of electrons is practically infinite. An example of a finite Fermi system is an atomic nucleus, having finite number of nucleons, protons and neutrons, which are fermions. Here we show that the fermion condensation manifests itself in finite Fermi systems as a forced merger of all, discreet for finite systems, single-particle levels, lying near the Fermi surface. On the first sight, this merger contradicts the standard Landau quasiparticle picture. Nevertheless, similar to inf…
The electron gas with short coherence length pairs: how to approach the stronger coupling limit?
2001
Abstract The attractive Hubbard model is investigated in 2D using a T -matrix approach. In a self-consistent calculation pairs as infinite lifetime Bosons only exist in the atomic limit and therefore a Fermi surface can be investigated also in the stronger coupling regime. A heavy quasiparticle peak with a weak dispersion crosses the Fermi surface at k F whereas light, single particle excitations do only exist far away from the Fermi surface. At low temperatures there seem to exist different self-consistent solutions. In one of them a pseudogap opens even in the integrated density of states. In the present work accurate k -dependent and k -integrated spectral quantities for a 2D finite latt…
Laser-induced collective excitations in a two-component Fermi gas
2002
We consider the linear density response of a two-component (superfluid) Fermi gas of atoms when the perturbation is caused by laser light. We show that various types of laser excitation schemes can be transformed into linear density perturbations, however, a Bragg spectroscopy scheme is needed for transferring energy and momentum into a collective mode. This makes other types of laser probing schemes insensitive for collective excitations and therefore well suited for the detection of the superfluid order parameter. We show that for the special case when laser light is coupled between the two components of the Fermi gas, density response is always absent in a homogeneous system.
Hartree-Fock-Bogoliubov theory of polarized Fermi systems
2008
Condensed Fermi systems with an odd number of particles can be described by means of polarizing external fields having a time-odd character. We illustrate how this works for Fermi gases and atomic nuclei treated by density functional theory or Hartree-Fock-Bogoliubov (HFB) theory. We discuss the method based on introducing two chemical potentials for different superfluid components, whereby one may change the particle-number parity of the underlying quasiparticle vacuum. Formally, this method is a variant of non-collective cranking, and the procedure is equivalent to the so-called blocking. We present and exemplify relations between the two-chemical-potential method and the cranking approxi…
Persistent currents in a circular array of Bose-Einstein condensates
2002
A ring-shaped array of Bose-Einstein condensed atomic gases can display circular currents if the relative phase of neighboring condensates becomes locked to certain values. It is shown that, irrespective of the mechanism responsible for generating these states, only a restricted set of currents are stable, depending on the number of condensates, on the interaction and tunneling energies, and on the total number of particles. Different instabilities due to quasiparticle excitations are characterized and possible experimental setups for testing the stability prediction are also discussed.
Decoherence of the Exciton and Decay of the Excitonic Polaron in Quantum Dots
2005
Bulk-phonon mechanisms of decoherence of an exciton confined in a quantum dot (QD) are considered in order to establish time limitations for the coherent control of the exciton with relevance to its application in quantum information processing. These are the formation and decay of the excitonic polaron. The estimations of characteristic dephasing times for the InAs/GaAs QD are discussed.
Quasiparticles and quantum phase transition in universal low-temperature properties of heavy-fermion metals
2006
We demonstrate, that the main universal features of the low temperature experimental $H-T$ phase diagram of CeCoIn5 and other heavy-fermion metals can be well explained using Landau paradigm of quasiparticles. The main point of our theory is that above quasiparticles form so-called fermion-condensate state, achieved by a fermion condensation quantum phase transition (FCQPT). When a heavy fermion liquid undergoes FCQPT, the fluctuations accompanying above quantum critical point are strongly suppressed and cannot destroy the quasiparticles. The comparison of our theoretical results with experimental data on CeCoIn5 have shown that the electronic system of above substance provides a unique opp…