Search results for "microwave"
showing 10 items of 693 documents
Partition function based analysis of cosmic microwave background maps
1999
We present an alternative method to analyse cosmic microwave background (CMB) maps. We base our analysis on the study of the partition function. This function is used to examine the CMB maps, making use of the different information embedded at different scales and moments. Using the partition function in a likelihood analysis in two dimensions (Qrms-PS, n), we find the best-fitting model to the best data available at present (the COBE–DMR 4 years data set). By means of this analysis we find a maximum in the likelihood function for n=1.8-0.65+0.35 and Qrms-PS = 10-2.5+3μ K (95 per cent confidence level) in agreement with the results of other similar analyses [Smoot et al. (1 yr), Bennet et a…
The evolution of the large-scale emission in Fanaroff-Riley type I jets
2011
Recent observations in X-rays and gamma-rays of nearby Fanaroff-Riley type I (FR I) radio galaxies have raised the question of the origin of the emission detected in the termination structures of their jets. The study of these structures can give information on the conditions for particle acceleration and radiation at the front shocks. In addition, an evolutionary scenario can help to disentangle the origin of the detected X-ray emission in young FR I sources, like some gigahertz peaked spectrum active galactic nuclei. This work focuses on the nature and detectability of the radiation seen from the termination regions of evolving FR I jets. We use the results of a relativistic, two-dimensio…
Complex temperature dependence of coupling and dissipation of cavity magnon polaritons from millikelvin to room temperature
2018
Hybridized magnonic-photonic systems are key components for future information processing technologies such as storage, manipulation or conversion of data both in the classical (mostly at room temperature) and quantum (cryogenic) regime. In this work, we investigate a YIG sphere coupled strongly to a microwave cavity over the full temperature range from $290\,\mathrm{K}$ down to $30\,\mathrm{mK}$. The cavity-magnon polaritons are studied from the classical to the quantum regime where the thermal energy is less than one resonant microwave quanta, i.e. at temperatures below $1\,\mathrm{K}$. We compare the temperature dependence of the coupling strength $g_{\rm{eff}}(T)$, describing the streng…
Ray-tracing through N-body simulations and CMB anisotropy estimations
2007
The fully nonlinear evolution of galaxy clusters and substructures –given by N-body simulations– is used to simulate maps of the Rees-Sciama (RS) effect. The universe is covered by simulation boxes and photons move across them. A recent technique for ray-tracing through N-body simulations is described in detail and implemented. It is based on the existence of preferred directions (to move photons through the boxes), and also on the use of an appropriate cutoff. By the moment, only small RS maps (around 2×2) have been obtained with this technique. We justify that our ray-tracing procedure is also appropriate in the case of large simulation cubes (∼ 1000 Mpc per edge), where high enough resol…
Gravitational Waves from an Axion-Dark Photon System: A Lattice Study
2021
In this work, we present a lattice study of an axion - dark photon system in the early Universe and show that the stochastic gravitational wave (GW) background produced by this system may be probed by future GW experiments across a vast range of frequencies. The numerical simulation on the lattice allows us to take into account non-linear backreaction effects and enables us to accurately predict the final relic abundance of the axion or axion-like particle (ALP) as well as its inhomogeneities, and gives a more precise prediction of the GW spectrum. Importantly, we find that the GW spectrum has more power at high momenta due to $2\rightarrow1$ processes. Furthermore, we find the degree of po…
Lens Effect and CMB Anisotropies: Simulations
2003
Cosmological structures deviate the photons of the Cosmic Microwave Background (CMB). The resulting deviations can be calculated moving photons in the gravitational field of realistic lens distributions obtained from numerical simulations. The main goal of this paper is answering the following question: Which types of numerical simulations are appropriate to study angular CMB deformations caused by lensing?
Doppler-free two-photon spectrum of SF_6 for metrological purposes
1998
We report on our systematic investigation of strong Doppler-free two-photon absorption in the middle infrared. The absorption frequencies for two counterpropagating waves of identical frequencies are predicted. Five of these transitions were observed with sub-Doppler resolution with a sideband CO(2) laser and were measured with 10-kHz accuracy. Knowledge of these strong two-photon absorptions frequencies will allow the improvement of secondary frequency standards in the infrared.
A dynamical dark energy model with a given luminosity distance
2011
It is assumed that the current cosmic acceleration is driven by a scalar field, the Lagrangian of which is a function of the kinetic term only, and that the luminosity distance is a given function of the red-shift. Upon comparison with Baryon Acoustic Oscillations (BAOs) and Cosmic Microwave Background (CMB) data the parameters of the models are determined, and then the time evolution of the scalar field is determined by the dynamics using the cosmological equations. We find that the solution is very different than the corresponding solution when the non-relativistic matter is ignored, and that the universe enters the acceleration era at larger red-shift compared to the standard $\Lambda CD…
Nonstationary oscillations in gyrotrons
2001
The onset of stochastic oscillations in gyrotrons is studied by means of the self-consistent theory describing nonstationary processes. Complicated alternating sequences of regions of stationary, automodulation, and chaotic oscillations are found in the plane of the generalized gyrotron variables: cyclotron resonance mismatch and dimensionless current. The results of the investigations are important in connection with attempts to increase the output power of gyrotrons by raising the current.
High selective H-plane TE dual mode cavity filter design by using nonresonating nodes
2013
The design of H-plane TE dual mode cavity filters using models containing nonresonating nodes is presented. From the models a coupling matrix is derived and decomposed into submatrices, each representing a subcircuit. The optimization and cascading of subcircuits represents a good starting point for the global optimization. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:161–166, 2014