4,941 research outputs found
Space environment robot vision system
A prototype twin-camera stereo vision system for autonomous robots has been developed at Goddard Space Flight Center. Standard charge coupled device (CCD) imagers are interfaced with commercial frame buffers and direct memory access to a computer. The overlapping portions of the images are analyzed using photogrammetric techniques to obtain information about the position and orientation of objects in the scene. The camera head consists of two 510 x 492 x 8-bit CCD cameras mounted on individually adjustable mounts. The 16 mm efl lenses are designed for minimum geometric distortion. The cameras can be rotated in the pitch, roll, and yaw (pan angle) directions with respect to their optical axes. Calibration routines have been developed which automatically determine the lens focal lengths and pan angle between the two cameras. The calibration utilizes observations of a calibration structure with known geometry. Test results show the precision attainable is plus or minus 0.8 mm in range at 2 m distance using a camera separation of 171 mm. To demonstrate a task needed on Space Station Freedom, a target structure with a movable I beam was built. The camera head can autonomously direct actuators to dock the I-beam to another one so that they could be bolted together
Platelet kinetics in the pulmonary microcirculation in vivo assessed by intravital microscopy
Growing evidence supports the substantial pathophysiological impact of platelets on the development of acute lung injury. Methods for studying these cellular mechanisms in vivo are not present yet. The aim of this study was to develop a model enabling the quantitative analysis of platelet kinetics and platelet-endothelium interaction within consecutive segments of the pulmonary microcirculation in vivo. New Zealand White rabbits were anesthetized and ventilated. Autologous platelets were separated from blood and labeled ex vivo with rhodamine 6G. After implantation of a thoracic window, microhemodynamics and kinetics of platelets were investigated by intravital microscopy. Velocities of red blood cells (RBCs) and platelets were measured in arterioles, capillaries and venules, and the number of platelets adhering to the microvascular endothelium was counted. Kinetics of unstimulated platelets was compared with kinetics of thrombin-activated platelets. Velocity of unstimulated platelets was comparable to RBC velocity in all vessel segments. Unstimulated platelets passed the pulmonary microcirculation without substantial platelet-endothelial interaction. In contrast, velocity of activated platelets was decreased in all vascular segments indicating platelet margination and temporal platelet-endothelium interaction. Thrombin-activated platelets adhered to arteriolar endothelium; in capillaries and venules adherence of platelets was increased 8-fold and 13-fold, respectively. In conclusion, using intravital microscopy platelet kinetics were directly analyzed in the pulmonary microcirculation in vivo for the first time. In contrast to leukocytes, no substantial platelet-endothelium interaction occurs in the pulmonary microcirculation without any further stimulus. In response to platelet activation, molecular mechanisms enable adhesion of platelets in arterioles and venules as well as retention of platelets within capillaries. Copyright (C) 2002 S. Karger AG, Basel
ISLAMIST TERRORIST ORGANIZATIONS IN AFRICA: A COMPARATIVE STUDY OF AL-SHABAAB AND BOKO HARAM
Terrorist activities have eroded the stability, development, and security of a growing number of African states.
The objective of this thesis is to better understand the terrorist groups Boko Haram and Al-Shabaab based on their strengths and weaknesses, and to identify their vulnerabilities in order to deduce their resilience to counterterrorism measures. The study also aims to shed light on the applied countermeasures. For this purpose, comparative case studies of two terrorist groups in Africa are presented, based on the available unclassified literature. The thesis adopts a qualitative approach to examine key elements of their organizational structures, ideologies, activities, and methods of recruitment and funding. In addition, the current counterterrorism efforts used on the African continent and their effectiveness are assessed.
The thesis identifies the exploitable vulnerabilities of the terrorist organizations as well as the ways in which they adapt in response to existing counterterrorism measures. Furthermore, it considers the relationship between centralized vs. decentralized organizational structures in the groups’ resilience to countermeasures. Based on the findings, it is clear that purely military approaches do not bring lasting solutions and need to be at least complemented by holistic measures. As such, the study is aimed at involved counterterrorism entities, the military, and scholars to improve the effectiveness of counterterrorism policies and measures.Oberstleutnant, German ArmyApproved for public release. Distribution is unlimited
Covariant Poisson equation with compact Lie algebras
The covariant Poisson equation for Lie algebra-valued mappings defined in
3-dimensional Euclidean space is studied using functional analytic methods.
Weighted covariant Sobolev spaces are defined and used to derive sufficient
conditions for the existence and smoothness of solutions to the covariant
Poisson equation. These conditions require, apart from suitable continuity,
appropriate local integrability of the gauge potentials and global weighted
integrability of the curvature form and the source. The possibility of
nontrivial asymptotic behaviour of a solution is also considered. As a
by-product, weighted covariant generalisations of Sobolev embeddings are
established.Comment: 31 pages, LaTeX2
New membership determination and proper motions of NGC 1817. Parametric and non-parametric approach
We have calculated proper motions and re-evaluated the membership
probabilities of 810 stars in the area of two NGC objects, NGC 1817 and NGC
1807. We have obtained absolute proper motions from 25 plates in the reference
system of the Tycho-2 Catalogue. The plates have a maximum epoch difference of
81 years; and they were taken with the double astrograph at Zo-Se station of
Shanghai Observatory, which has an aperture of 40 cm and a plate scale of 30
arcsec/mm. The average proper motion precision is 1.55 mas/yr. These proper
motions are used to determine the membership probabilities of stars in the
region, based on there being only one very extended physical cluster: NGC 1817.
With that aim, we have applied and compared parametric and non-parametric
approaches to cluster/field segregation. We have obtained a list of 169
probable member stars.Comment: 11 pages, 8 figures, A&A in pres
Pleniglacial sedimentation process reconstruction on laminated lacustrine sediments from lava-dammed Paleolake Alf, West Eifel Volcanic Field (Germany)
Critical behavior of colloid-polymer mixtures in random porous media
We show that the critical behavior of a colloid-polymer mixture inside a
random porous matrix of quenched hard spheres belongs to the universality class
of the random-field Ising model. We also demonstrate that random-field effects
in colloid-polymer mixtures are surprisingly strong. This makes these systems
attractive candidates to study random-field behavior experimentally.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let
Amplification of different marker sequences for identification of Agrobacterium vitis strains
Research Not
Non-existence of Ramanujan congruences in modular forms of level four
Ramanujan famously found congruences for the partition function like p(5n+4)
= 0 modulo 5. We provide a method to find all simple congruences of this type
in the coefficients of the inverse of a modular form on Gamma_{1}(4) which is
non-vanishing on the upper half plane. This is applied to answer open questions
about the (non)-existence of congruences in the generating functions for
overpartitions, crank differences, and 2-colored F-partitions.Comment: 19 page
- …