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High-speed multi-dimensional relative navigation for uncooperative space objects
This work proposes a high-speed Light Detection and Ranging (LIDAR) based navigation architecture that is appropriate for uncooperative relative space navigation applications. In contrast to current solutions that exploit 3D LIDAR data, our architecture transforms the odometry problem from the 3D space into multiple 2.5D ones and completes the odometry problem by utilizing a recursive filtering scheme. Trials evaluate several current state-of-the-art 2D keypoint detection and local feature description methods as well as recursive filtering techniques on a number of simulated but credible scenarios that involve a satellite model developed by Thales Alenia Space (France). Most appealing performance is attained by the 2D keypoint detector Good Features to Track (GFFT) combined with the feature descriptor KAZE, that are further combined with either the H∞ or the Kalman recursive filter. Experimental results demonstrate that compared to current algorithms, the GFTT/KAZE combination is highly appealing affording one order of magnitude more accurate odometry and a very low processing burden, which depending on the competitor method, may exceed one order of magnitude faster computation
ILIAD Testing; and a Kalman Filter for 3-D Pose Estimation
This report presents the results of a two-part project. The first part presents results of performance assessment tests on an Internet Library Information Assembly Data Base (ILIAD). It was found that ILLAD performed best when queries were short (one-to-three keywords), and were made up of rare, unambiguous words. In such cases as many as 64% of the typically 25 returned documents were found to be relevant. It was also found that a query format that was not so rigid with respect to spelling errors and punctuation marks would be more user-friendly. The second part of the report shows the design of a Kalman Filter for estimating motion parameters of a three dimensional object from sequences of noisy data derived from two-dimensional pictures. Given six measured deviation values represendng X, Y, Z, pitch, yaw, and roll, twelve parameters were estimated comprising the six deviations and their time rate of change. Values for the state transiton matrix, the observation matrix, the system noise covariance matrix, and the observation noise covariance matrix were determined. A simple way of initilizing the error covariance matrix was pointed out
Using Instanton Theory to Study Quantum Effects in Photosensitization
Electronic excitation is usually accomplished using light (photoexcitation) and is a key step in a vast number of important physical and biological processes. However, in instances where photoexcitation is not possible, a photosensitizer can excite the target molecule in a process called photosensitization. Unfortunately, full details of its mechanism are still unknown. This perspective gives an overview of the current understanding of photosensitization and describes how instanton theory can be used to fill the gaps, especially with regard tothe importance of quantum tunnelling effects
On the Nature of Incompressible Magnetohydrodynamic Turbulence
A novel model of incompressible magnetohydrodynamic turbulence in the
presence of a strong external magnetic field is proposed for explanation of
recent numerical results. According to the proposed model, in the presence of
the strong external magnetic field, incompressible magnetohydrodynamic
turbulence becomes nonlocal in the sense that low frequency modes cause
decorrelation of interacting high frequency modes from the inertial interval.
It is shown that the obtained nonlocal spectrum of the inertial range of
incompressible magnetohydrodynamic turbulence represents an anisotropic
analogue of Kraichnan's nonlocal spectrum of hydrodynamic turbulence. Based on
the analysis performed in the framework of the weak coupling approximation,
which represents one of the equivalent formulations of the direct interaction
approximation, it is shown that incompressible magnetohydrodynamic turbulence
could be both local and nonlocal and therefore anisotropic analogues of both
the Kolmogorov and Kraichnan spectra are realizable in incompressible
magnetohydrodynamic turbulence.Comment: Physics of Plasmas (Accepted). A small chapter added about 2D MHD
turbulenc
X-ray emission from PSR B1800-21, its wind nebula, and similar systems
We detected X-ray emission from PSR B1800-21 and its synchrotron nebula with
the Chandra X-ray Observatory. The pulsar's observed flux is (1.4+/-0.2)
10^{-14} ergs cm^{-2} s^{-1} in the 1-6 keV band. The spectrum can be described
by a two-component PL+BB model, suggesting a mixture of thermal and
magnetospheric emission. For a plausible hydrogen column density n_{H}=1.4
10^{22} cm^{-2}, the PL component has a slope Gamma=1.4+/-0.6 and a luminosity
L_{psr}^{nonth}=4 10^{31}(d/4 kpc)^2 ergs s^{-1}. The properties of the thermal
component (kT=0.1-0.3 keV, L^{bol}=10^{31}-10^{33} ergs s^{-1}) are very poorly
constrained because of the strong interstellar absorption. The compact,
7''\times4'', inner pulsar-wind nebula (PWN), elongated perpendicular to the
pulsar's proper motion, is immersed in a fainter asymmetric emission. The
observed flux of the PWN is (5.5+/-0.6) 10^{-14} ergs cm^{-2} s^{-1} in the 1-8
keV band. The PWN spectrum fits by a PL model with Gamma=1.6+/-0.3, L=1.6
10^{32} (d/4 kpc})^2 ergs s^{-1}. The shape of the inner PWN suggests that the
pulsar moves subsonically and X-ray emission emerges from a torus associated
with the termination shock in the equatorial pulsar wind. The inferred
PWN-pulsar properties (e.g., the PWN X-ray efficiency, L_{pwn}/\dot{E}~10^{-4};
the luminosity ratio, L_{pwn}/L_{psr}^{nonth}=4; the pulsar wind pressure at
the termination shock, p_s=10^{-9} ergs cm^{-3}) are very similar to those of
other subsonically moving Vela-like objects detected with Chandra
(L_{pwn}/\dot{E}=10^{-4.5}-10^{-3.5}, L_{pwn}/L_{psr}^{nonth}~5,
p_s=10^{-10}-10^{-8} ergs cm^{-1}).Comment: 11 pages, 10 figures, 2 tables; submitted to ApJ. Version with the
high-resolution figures is available at
http://www.astro.psu.edu/users/green/B1800/B1800_ApJ.pd
Curriculum construction and custom publishing - an academic perspective
Increasingly, changes in the policies of university, government and professional bodies demand that subject and course design are role or outcome driven with articulated graduate attributes. This has had an immediate impact on both the academics designing subjects and the publishers responding to their needs with customized resources or 'custom publishing'
Thermogravimetric analysis of aluminised E-glass fibre reinforced unsaturated polyester composites
Novel aluminised E-glass fibre reinforced unsaturated polyester composites, originally formulated for enhanced thermal and electrical shielding properties were evaluated in terms of their thermal performance. The thermal degradation of these specimens was analysed using a thermogravimetric analyser (TGA). The samples were heated from ambient temperature to 500 °C at a heating rate of 20 °C/min. All specimens were decomposed under dry nitrogen (N2) at a flow rate of 40 ml/min to yield gases and solid char. Aluminised E-glass composites were compared alongside the unmetallised E-glass and unreinforced composite. The major weight loss occurred between 200 and 400 °C. The unreinforced polyester had a maximum weight loss, 1.25%/°C, occurring at 360 °C. For the aluminised and unmetallised E-glass composites, the maximum rate of weight loss was 0.34 and 0.55%/°C, respectively. Experimental results show the degradation of the aluminised E-glass composites obtained from TGA tests is higher compared to those of unmetallised E-glass fibre and unreinforced polyester composite. This improvement is correlated to the aluminium coating.http://www.sciencedirect.com/science/article/B6TXX-4M2WP4H-2/1/bef16e64695f47cabc7a3f55ce5b745
Geometry and violent events in turbulent pair dispersion
The statistics of Lagrangian pair dispersion in a homogeneous isotropic flow
is investigated by means of direct numerical simulations. The focus is on
deviations from Richardson eddy-diffusivity model and in particular on the
strong fluctuations experienced by tracers. Evidence is obtained that the
distribution of distances attains an almost self-similar regime characterized
by a very weak intermittency. The timescale of convergence to this behavior is
found to be given by the kinetic energy dissipation time measured at the scale
of the initial separation. Conversely the velocity differences between tracers
are displaying a strongly anomalous behavior whose scaling properties are very
close to that of Lagrangian structure functions. These violent fluctuations are
interpreted geometrically and are shown to be responsible for a long-term
memory of the initial separation. Despite this strong intermittency, it is
found that the mixed moment defined by the ratio between the cube of the
longitudinal velocity difference and the distance attains a statistically
stationary regime on very short timescales. These results are brought together
to address the question of violent events in the distribution of distances. It
is found that distances much larger than the average are reached by pairs that
have always separated faster since the initial time. They contribute a
stretched exponential behavior in the tail of the inter-tracer distance
probability distribution. The tail approaches a pure exponential at large
times, contradicting Richardson diffusive approach. At the same time, the
distance distribution displays a time-dependent power-law behavior at very
small values, which is interpreted in terms of fractal geometry. It is argued
and demonstrated numerically that the exponent converges to one at large time,
again in conflict with Richardson's distribution.Comment: 21 page
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