1,440 research outputs found
RF system model for In-band full duplex communications
Abstract. In recent years by increasing the demands for communication services various technologies are examined in order to improve the throughput and spectrum efficiency of the wireless communication systems. For improving the performance a communication network, system deficiencies such as transmitter and receiver impairments need to be removed or compensated. One way to improve the network efficiency is to employ full duplex technology. Full duplex technology doubles the network capacity compared to the case when typical frequency division duplexing (FDD) or time division duplexing (TDD) are employed in a transceiver design.
Although full duplex (FD) technology has enhanced the performance of the radio communication devices, the main challenge in full duplex communication is the leaking self-interference signal from the transmitter to the receiver. Different methods are employed to suppress the self-interference signal in digital and analog domains which are categorized as passive or active cancellations. These techniques are discussed in this thesis in order to understand from which point in the propagation path, the required signal for cancellation can be taken and how those techniques are employed in digital and analog domains. For having a good self-interference cancellation (SIC) both analog and digital cancellation techniques are needed since typical digital suppression method is low complex and somewhat limited.
In this thesis, first we start with discussing about the full duplex technology and the reason why it has become popular in recent years and later full duplex deficiencies are examined. In the following chapters different cancellation methods are introduced and some results are provided in Chapter 5
Fermat's principle in quantum gravitational optics
Interactions incorporating the vacuum polarization effects in curved
backgrounds modify the null cone structure in such a way that the photon
trajectories would not be the space-time geodesics anymore. The gravitational
birefringence introduced as a direct consequence of these effects, will allow
shifts in the photon velocities leading to polarization dependent superluminal
propagation. Taking these effects into account we study Fermat's principle in
the context of the 1+3 (threading) formulation of the space-time decomposition.
We find an expression for the modified spacetime refractive index and show it
is proportional to the light cone correction to the first order. Consequences
of this modification on polarization sum rules and spatial light paths are
considered.Comment: 13 Pages, REVTex format, section on gravitomagnetic monopoles is
removed along with its references, new references adde
Boundary layer simulator improvement
Boundary Layer Integral Matrix Procedure (BLIMPJ) has been identified by the propulsion community as the rigorous boundary layer program in connection with the existing JANNAF reference programs. The improvements made to BLIMPJ and described herein have potential applications in the design of the future Orbit Transfer Vehicle engines. The turbulence model is validated to include the effects of wall roughness and a way is devised to treat multiple smooth-rough surfaces. A prediction of relaminarization regions is examined as is the combined effects of wall cooling and surface roughness on relaminarization. A turbulence model to represent the effects of constant condensed phase loading is given. A procedure is described for thrust decrement calculation in thick boundary layers by coupling the T-D Kinetics Program and BLIMPJ and a way is provided for thrust loss optimization. Potential experimental studies in rocket nozzles are identified along with the required instrumentation to provide accurate measurements in support of the presented new analytical models
Simulation of Acoustic Black Hole in a Laval Nozzle
A numerical simulation of fluid flows in a Laval nozzle is performed to
observe formations of acoustic black holes and the classical counterpart to
Hawking radiation under a realistic setting of the laboratory experiment. We
determined the Hawking temperature of the acoustic black hole from obtained
numerical data. Some noteworthy points in analyzing the experimental data are
clarified through our numerical simulation.Comment: 26 pages, published versio
Evolution of the Magnetized, Neutrino-Cooled Accretion Disk in the Aftermath of a Black Hole Neutron Star Binary Merger
Black hole-torus systems from compact binary mergers are possible engines for
gamma-ray bursts (GRBs). During the early evolution of the post-merger remnant,
the state of the torus is determined by a combination of neutrino cooling and
magnetically-driven heating processes, so realistic models must include both
effects. In this paper, we study the post-merger evolution of a magnetized
black hole-neutron star binary system using the Spectral Einstein Code (SpEC)
from an initial post-merger state provided by previous numerical relativity
simulations. We use a finite-temperature nuclear equation of state and
incorporate neutrino effects in a leakage approximation. To achieve the needed
accuracy, we introduce improvements to SpEC's implementation of
general-relativistic magnetohydrodynamics (MHD), including the use of
cubed-sphere multipatch grids and an improved method for dealing with
supersonic accretion flows where primitive variable recovery is difficult. We
find that a seed magnetic field triggers a sustained source of heating, but its
thermal effects are largely cancelled by the accretion and spreading of the
torus from MHD-related angular momentum transport. The neutrino luminosity
peaks at the start of the simulation, and then drops significantly over the
first 20\,ms but in roughly the same way for magnetized and nonmagnetized
disks. The heating rate and disk's luminosity decrease much more slowly
thereafter. These features of the evolution are insensitive to grid structure
and resolution, formulation of the MHD equations, and seed field strength,
although turbulent effects are not fully convergedComment: 17 pages, 18 figure
A single layer deposition of Li-doped mesoporous TiO<sub>2</sub> beads for low-cost and efficient dye-sensitized solar cells
A shortened version of the Dementia Drivers’ Screening Assessment
Introduction: Cognitive tests are used to inform recommendations about the safety of people with dementia to continue driving. The Dementia Drivers’ Screening Assessment (DDSA) is a neuropsychological battery designed to assist in this process. However, it is lengthy to administer and requires materials from various test batteries.
Aims: The primary aim of this study was to develop a shortened version of the DDSA for individuals with dementia.
Methods: Data on participants with dementia from two studies were analysed. These participants were all drivers with dementia who were identified by community mental health teams and psychiatrists. Each participant was assessed on the DDSA and also assessed on-road by an ‘approved driving instructor’ using the Nottingham Neurological Driving Assessment.
Results: This study analysed 102 participants, who had a mean age of 74.0 (SD=7.7) years and of whom 80 (78%) were men. Twenty three drivers were judged to be unsafe and 79 safe. The agreement between the short version and on-road assessment was 79%. The assessment was better at detecting safe drivers than unsafe drivers.
Conclusion: The findings suggested that the shortened DDSA is suitable for participants who are unable or do not wish to undergo lengthier assessment
Separability of Rotational Effects on a Gravitational Lens
We derive the deflection angle up to due to a Kerr gravitational
lens with mass and specific angular momentum . It is known that at the
linear order in and the Kerr lens is observationally equivalent to the
Schwarzschild one because of the invariance under the global translation of the
center of the lens mass. We show, however, nonlinear couplings break the
degeneracy so that the rotational effect becomes in principle separable for
multiple images of a single source. Furthermore, it is distinguishable also for
each image of an extended source and/or a point source in orbital motion. In
practice, the correction at becomes for the
supermassive black hole in our galactic center. Hence, these nonlinear
gravitational lensing effects are too small to detect by near-future
observations.Comment: 12 pages (RevTeX); accepted for publication in Phys. Rev.
Gravitational lensing by stars with angular momentum
Gravitational lensing by spinning stars, approximated as homogeneous spheres,
is discussed in the weak field limit. Dragging of inertial frames, induced by
angular momentum of the deflector, breaks spherical symmetry. I examine how the
gravito-magnetic field affects image positions, caustics and critical curves.
Distortion in microlensing-induced light curves is also considered.Comment: 9 pages, 9 figures; to appear in MNRA
- …