721 research outputs found
Development of a truss joint for robotic assembly of space structures
This report presents the results of a detailed study of mechanical fasteners which were designed to facilitate robotic assembly of structures. Design requirements for robotic structural assembly were developed, taking into account structural properties and overall system design, and four candidate fasteners were designed to meet them. These fasteners were built and evaluated in the laboratory, and the Hammer-Head joint was chosen as superior overall. It had a high reliability of fastening under misalignments of 2.54 mm (0.1 in) and 3 deg, the highest end fixity (2.18), the simplest end effector, an integral capture guide, good visual verification, and the lightest weight (782 g, 1.72 lb). The study found that a good design should incorporate chamfers sliding on chamfers, cylinders sliding on chamfers, and hard surface finishes on sliding surfaces. The study also comments on robot flexibility, sag, hysteresis, thermal expansion, and friction which were observed during the testing
Robot-friendly connector
Robot friendly connectors, which, in one aspect, are truss joints with two parts, a receptacle and a joint, are presented. The joints have a head which is loosely inserted into the receptacle and is then tightened and aligned. In one aspect, the head is a rounded hammerhead which initially is enclosed in the receptacle with sloppy fit provided by the shape, size, and configuration of surfaces on the head and on the receptacle
Overview of the NASA Docking System (NDS) and the International Docking System Standard (IDSS)
The NASA/JSC Engineering Directorate has been developing the technology for a Low Impact Docking System (LIDS) for many years. LIDS had been chosen to be the Constellation Program baseline. In February 2009, the International Space Station (ISS) Multilateral control Board (MCB) began an initiative to develop an International Docking System Standard (IDSS) to facilitate greater international cooperation in space and enable emergency crew rescue missions. Discussions as to whether the LIDS could be made compatible with the IDSS were under way. With the cancellation of the Constellation Program, NASA made a policy decision to convert both of the docking ports on the United States On-orbit Segment (USOS) to IDSS ports and NASA moved the LIDS project under the ISS Program. LIDS was redesigned to become the NASA implementation of the emerging IDSS, and its name was changed to the NASA Docking System (NDS). The NDS design will be certified as a gblack box h which can be integrated onto vehicles planning to dock to the ISS IDSS ports. This presentation will discuss the evolution of the IDSS from both the LIDS and the Androgynous Peripheral Assembly System (APAS) and outline the interface requirements which are given in the IDSS Interface Definition Document (IDD). It also will give an overview of the current NDS design, and touch on ISS plans for converting its docking ports to be IDSS compliant
Fourier transform based procedure for investigations on the grid frequency signal
The continuous growth of PV and wind sources makes the inertia of power systems decrease and creates larger frequency deviations. Frequency oscillation is a stochastic signal and, consequently, it could be complex to compare the effectiveness of different control approaches devoted to manage this problem. In this paper a Fourier transform procedure is proposed in order to define a standard frequency oscillation and to set up the dynamic model of the electric grid. The final goal is to numerically simulate a realistic transient behavior; using this grid, such a model results to be the ideal starting point for evaluating the effectiveness of different possible approaches to manage the energy balance problem
Structure of the magnetoionic medium around the FR Class I radio galaxy 3C 449
The goal of this work is to constrain the strength and structure of the
magnetic field associated with the environment of the radio source 3C 449,
using observations of Faraday rotation, which we model with a structure
function technique and by comparison with numerical simulations. We assume that
the magnetic field is a Gaussian, isotropic random variable and that it is
embedded in the hot intra-group plasma surrounding the radio source. For this
purpose, we present detailed rotation measure images for the polarized radio
source 3C 449, previously observed with the Very Large Array at seven
frequencies between 1.365 and 8.385 GHz. We quantify the statistics of the
magnetic-field fluctuations by deriving rotation measure structure functions,
which we fit using models derived from theoretical power spectra. We quantify
the errors due to sampling by making multiple two-dimensional realizations of
the best-fitting power spectrum.We also use depolarization measurements to
estimate the minimum scale of the field variations. We then make
three-dimensional models with a gas density distribution derived from X-ray
observations and a random magnetic field with this power spectrum. Under these
assumptions we find that both rotation measure and depolarization data are
consistent with a broken power-law magnetic-field power spectrum, with a break
at about 11 kpc and slopes of 2.98 and 2.07 at smaller and larger scales
respectively. The maximum and minimum scales of the fluctuations are around 65
and 0.2 kpc, respectively. The average magnetic field strength at the cluster
centre is 3.5 +/-1.2 micro-G, decreasing linearly with the gas density within
about 16 kpc of the nucleus.Comment: 19 pages; 14 figures; accepted for publication on A&A. For a high
quality version use ftp://ftp.eso.org/pub/general/guidetti
Jet triggered Type Ia supernovae in radio-galaxies?
We report the serendipitous discovery of a supernova (SN) in the nearby
radio-galaxy 3C 78. Observations obtained with the STIS spectrograph on board
the Hubble Space Telescope show, at a distance of 0.54 arcsec (300 pc) from the
galaxy nucleus, a second bright source, not present in previous images. As this
source was fortuitously covered by the spectrograph slit its spectrum was
obtained and it is characteristic of a Type Ia SN. This SN is closely aligned
with the radio-jet of 3C 78. Analysis of historical records shows that such a
close association between jet and supernova occurred in 6 of the 14 reported
SNe in radio-galaxies. The probability that this results from a random
distribution of SN in the host galaxy is less than 0.05%. We then argue that
jets might trigger supernova explosions.Comment: 9 pages, 3 figures, 1 table, to appear in ApJL, 20 Jul 200
A homogeneização de gêneros literários nos filmes de Walt Disney
Este artigo é o desenvolvimento de um trabalho já apresentado anteriormente, que pretende estudar o processo de adaptação de obras literárias consagradas em filmes de animação do estúdio Walt Disney, mostrando como essas obras, de diferentes gêneros literários, com diferentes características, acabam por ser moldadas de uma forma homogênea para que se tornem obras típicas da empresa em questão. Serão descritos os gêneros literários considerados, o conto de fadas e o romance do século XIX, bem como um rápido resumo da obra original e do filme adaptado, para que se possa fazer um paralelo entre eles. Este é um recorte do trabalho original, para que ele possa se enquadrar nos moldes dessa publicação proposta
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