1,714 research outputs found
Gravitational Microlensing of a Reverberating Quasar Broad Line Region - I. Method and Qualitative Results
The kinematics and morphology of the broad emission line region (BELR) of
quasars are the subject of significant debate. The two leading methods for
constraining BELR properties are microlensing and reverberation mapping. Here
we combine these two methods with a study of the microlensing behaviour of the
BELR in Q2237+0305, as a change in continuum emission (a "flare") passes
through it. Beginning with some generic models of the BELR - sphere, bicones,
disk - we slice in velocity and time to produce brightness profiles of the BELR
over the duration of the flare. These are numerically microlensed to determine
whether microlensing of reverberation mapping provides new information about
the properties of BELRs. We describe our method and show images of the models
as they are flaring, and the unlensed and lensed spectra that are produced.
Qualitative results and a discussion of the spectra are given in this paper,
highlighting some effects that could be observed. Our conclusion is that the
influence of microlensing, while not strong, can produce significant observable
effects that will help in differentiating the properties of BELRs.Comment: 17 pages, 14 low resolution figures, 1 table, accepted for MNRAS. v2:
Corrected velocities p16, 8 to 0.08, 9 to 0.0
In situ visualization by X-Ray computed tomography on sulfur stabilization and lithium polysulfides immobilization in S@HCS/MnOâ cathode
The lithium-sulfur (Li-S) batteries have high theoretical energy density, exceeding that of the lithium-ion batteries. However, their practical applications are hindered by the capacity decay due to lithium polysulfide shuttle effect and sulfur volume expansion. Here, we design a S@hollow carbon with porous shell/MnOx (S@HCS/MnOx) cathode to accommodate and immobilize sulfur and polysulfides, and develop a non-destructive technique X-ray computed tomography (X-ray CT) to in situ visualize the volume expansion of Li-S cathode. The designed cathode achieves a specific capacity of âŒ1100 mAh g-1 at 0.2âŻC with a fade rate of 0.18% per cycle over 300 cycles. The X-ray CT shows that only 16% volume expansion and 70% volume fraction of solid sulfur remaining in the S@HCS/MnOx cathode, superior to the commercial cathode with 40% volume expansion and 5% volume remaining of solid sulfur particles. This is the first reported visualization evidence for the effectiveness of hollow carbon structure in accommodating cathode volume expansion and immobilizing sulfur shuttling. X-ray CT can serve as a powerful in situ tool to trace the active materials and then feedback to the structure design, which helps develop efficient and reliable energy storage systems
Substructure in lensing clusters and simulations
We present high-resolution mass reconstructions for five massive
cluster-lenses spanning a redshift range from --0.57 utilising
archival {\it Hubble Space Telescope} ({\it HST}) data and applying
galaxy-galaxy lensing techniques. These detailed mass models were obtained from
the observations by combining constraints from the strong and weak lensing
regimes. We ascribe local weak distortions in the shear maps to perturbations
induced by the presence of galaxy haloes around individual bright early-type
cluster member galaxies. This technique constrains the mass enclosed within an
aperture for these subhaloes. We are sensitive to a specific mass range for
these subhaloes, -- 10^{12.5} \msun, which we associate with
galaxy-scale subhaloes. Adopting a parametric model for the subhaloes, we also
derive their velocity dispersion function and the aperture radius function. The
mass spectrum of substructure in the inner regions of the observed clusters is
directly compared with that in simulated clusters extracted from the {\it
Millennium Simulation}. The massfunction, aperture radii and velocity
dispersion function are compared in detail. Overall, we find good agreement
between the distribution of substructure properties retrieved using the lensing
analysis and those obtained from the simulation (truncated abstract).Comment: 15 pages, 5 figures, 2 tables, in press MNRA
Radio frequency channel characterization for energy harvesting in factory environments
This thesis presents ambient energy data obtained from a measurement campaign carried out at an automobile plant. At the automobile plant, ambient light, ambient temperature
and ambient radio frequency were measured during the day time over two days. The measurement results showed that ambient light generated the highest DC power. For plant and operation managers at the automobile plant, the measurement data can be used in system design considerations for future energy harvesting wireless sensor nodes at the plant.
In addition, wideband measurements obtained from a machine workshop are presented in this thesis. The power delay profile of the wireless channel was obtained by using a frequency domain channel sounding technique. The measurements were compared with
an equivalent ray tracing model in order to validate the suitability of the commercial propagation software used in this work.
Furthermore, a novel technique for mathematically recreating the time dispersion created by factory inventory in a radio frequency channel is discussed. As a wireless receiver
design parameter, delay spread characterizes the amplitude and phase response of the radio channel. In wireless sensor devices, this becomes paramount, as it determines the
complexity of the receiver. In reality, it is sometimes difficult to obtain full detail floor plans of factories for deterministic modelling or carry out spot measurements during
building construction. As a result, radio provision may be suboptimal. The method presented in this thesis is based on 3-D fractal geometry. By employing the fractal overlaying algorithm presented, metallic objects can be placed on a floor plan so as to
obtain similar radio frequency channel effects. The environment created using the fractal approach was used to estimate the amount of energy a harvesting device can accumulate
in a University machine workshop space
Recent Developments in Numerical Electron Optics
The familiar methods for the numerical calculation of fields in electron optical devices are outlined briefly. for the solution of self- adjoint elliptic differential equations in orthogonal curvilinear coordinate systems a favourable ninepoint discretization is worked out which can be applied favourably e.g. to spherical mesh grids. The field calculation in magnetic deflection systems by means of an integral equation method is also highly advantageous. The methods for the field calculation can be still more improved by means of suitable hybrid procedures.
A second and shorter contribution is concerned with ray tracing and aberrations. Some favourable numerically stable new forms of the ray equation are derived and thereafter a new simple method for the determination of aberrations is outlined
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