6,948 research outputs found
Performance Improvement of QPSK Signal Predetection EGC Diversity Receiver
This paper proposes a modification of quadrature phase-shift-keying (QPSK) signal diversity reception with predetection equal gain combiner (EGC). The EGC combining is realized by using the constant modulus algorithm (CMA). Carrier synchronization is performed by the phase locked loop (PLL). Comparative analysis of the modified and ordinary diversity receiver in the presence of carrier frequency offset in the additive white Gaussian noise (AWGN) channel, as well as in Rician fading channel is shown. The proposed diversity receiver allows significant frequency offset compared to the diversity receiver that uses only PLL, and the error probability of the proposed receiver is very close to the error probability of the receiver with only PLL and zero frequency offset. The functionality of the proposed diversity receiver, as well as its properties is experimentally verified on a system based on universal software radio peripheral (USRP) hardware. The performed comparison confirms the expected behavior of the system
Symmetry Based Properties of the Transition Metal Dichalcogenide Nanotubes
The full geometrical symmetry groups (the line groups) of the monolayered,
2Hb and 3R polytypes of the inorganic MoS2 and WS2 micro- and nanotubes of
arbitrary chirality are found. This is used to find the coordinates of the
representative atoms sufficient to determine completely geometrical structure
of tubes. Then some physical properties which can be deduced from the symmetry
are discussed: electron band degeneracies, selection rules, general forms of
the second rank tensors and potentials, phonon spectra.Comment: 6 pages 1 figur
Inelastic collisions of relativistic electrons with atomic targets assisted by a laser field
We consider inelastic collisions between relativistic electrons and atomic
targets assisted by a low-frequency laser field in the case when this field is
still much weaker than the typical internal fields in the target. Concentrating
on target transitions we show that they can be substantially affected by the
presence of the laser field. This may occur either via strong modifications in
the motion of the relativistic electrons caused by the electron-laser
interaction or via the Compton effect when the incident electrons convert laser
photon(s) into photons with frequencies equal to target transition frequencies.Comment: 4 pages, 2 figure
Evolution of multi-gap superconductivity in the atomically thin limit: Strain-enhanced three-gap superconductivity in monolayer MgB
Starting from first principles, we show the formation and evolution of
superconducting gaps in MgB at its ultrathin limit. Atomically thin MgB
is distinctly different from bulk MgB in that surface states become
comparable in electronic density to the bulk-like - and -bands.
Combining the ab initio electron-phonon coupling with the anisotropic
Eliashberg equations, we show that monolayer MgB develops three distinct
superconducting gaps, on completely separate parts of the Fermi surface due to
the emergent surface contribution. These gaps hybridize nontrivially with every
extra monolayer added to the film, owing to the opening of additional coupling
channels. Furthermore, we reveal that the three-gap superconductivity in
monolayer MgB is robust over the entire temperature range that stretches up
to a considerably high critical temperature of 20 K. The latter can be boosted
to 50 K under biaxial tensile strain of 4\%, which is an enhancement
stronger than in any other graphene-related superconductor known to date.Comment: To appear in Phys. Re
Irreducible Representations of Diperiodic Groups
The irreducible representations of all of the 80 diperiodic groups, being the
symmetries of the systems translationally periodical in two directions, are
calculated. To this end, each of these groups is factorized as the product of a
generalized translational group and an axial point group. The results are
presented in the form of the tables, containing the matrices of the irreducible
representations of the generators of the groups. General properties and some
physical applications (degeneracy and topology of the energy bands, selection
rules, etc.) are discussed.Comment: 30 pages, 5 figures, 28 tables, 18 refs, LaTex2.0
Control of Intense Laser- Atom Processes With Strong Static Fields
Atomic processes in the presence of intense fields continue to attract a great deal of attention [1-3]. Key goals of research in this area are to increase the intensities and frequencies of coherent light produced in these processes. In two recent works [4,5] we have demonstrated theoretically the possibility of controlling intense laser-atom interaction processes by employing strong, but experimentally feasible, static electric or magnetic fields. Thus, in Ref. [4] we demonstrated how a strong static electric field may induce a high-energy plateau for scattered x-ray photons in laser-assisted, x-ray-atom scattering in which the incident x-rays were assumed to have an energy of 50 eV. The scattered x-rays were shown to have energies up to well over 200 eV, making such a process an attractive one for realizing coherent x-rays in the water window [between the K shell absorption edges of C (284 eV) and 0 (532 eV)], which would have important applications to imaging living biological structures by means of x-ray holography [6]. In Ref. [5], we demonstrated control of high-harmonic generation (HHG) by a linearly polarized laser field using a uniform static magnetic field parallel to the laser polarization. We predicted that particular values of the magnetic field can increase harmonic intensities by orders of magnitude. Our classical orbit calculations showed that these magnetic-field-induced intensity revivals occur when the return time for laserdriven motion of the electron back to the origin is a multiple of the cyclotron period for motion perpendicular to the laser polarization direction. We present here further results [7-9] on using strong electric and magnetic fields to control these two intense laser-atom processes
UWB System Performance Improvement Using Smart Interference Rejection Filter
In this paper we proposed a smart interference rejection filter in TH-PPM UWB system, which improves the system\'s error probability for an order of magnitude in case of high power OFDM interference. The smart filter is based on an adaptive transversal filter. Based on the fulfillment of certain conditions, the filter activates or deactivates some parts of it
THE BEHAVIOUR OF MUSCLES IN EXTERNAL INSTANTANEOUS FORCE FIELDS
The purpose of this study is to analyze the behaviour of muscles in an external instantaneous force field. A model is presented which provides a qualitative assessment of what occurs when muscles react to a strong strike or a sudden jerk.
In the context of the model, it has been noticed that fine muscles reacted to a strike or jerk differently to massive muscles
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