2,412 research outputs found
Simulation, modelling and development of the metris RCA
In partnership with Metris UK we discuss the utilisation of modelling and simulation methods in the development of a revolutionary 7-axis Robot CMM Arm (RCA). An offline virtual model is described, facilitating pre-emptive collision avoidance and assessment of optimal placement of the RCA relative to scan specimens. Workspace accessibility of the RCA is examined under a range of geometrical assumptions and we discuss the effects of arbitrary offsets resulting from manufacturing tolerances. Degeneracy is identified in the number of ways a given pose may be attained and it is demonstrated how a simplified model may be exploited to solve the inverse kinematics problem of finding the âcorrectâ set of joint angles. We demonstrate how the seventh axis may be utilised to avoid obstacles or otherwise awkward poses, giving the unit greater dexterity than traditional CMMs. The results of finite element analysis and static force modelling on the RCA are presented which provide an estimate of the forces exerted on the internal measurement arm in a range of poses
Characteristics, accuracy and reverification of robotised articulated arm CMMs
VDI article 2617 specifies characteristics to describe the accuracy of articulated arm coordinate measuring machines (AACMMs) and outlines procedures for checking them. However the VDI prescription was written with a former generation of machines in mind: manual arms exploiting traditional touch probe technologies. Recent advances in metrology have given rise to noncontact laser scanning tools and robotic automation of articulated arms â technologies which are not adequately characterised using the VDI specification. In this paper we examine the âguidelinesâ presented in VDI 2617, finding many of them to be ambiguous and open to interpretation, with some tests appearing even to be optional. The engineer is left significant flexibility in the execution of the test procedures and the manufacturer is free to specify many of the test parameters. Such flexibility renders the VDI tests of limited value and the results can be misleading. We illustrate, with examples using the Nikon RCA, how a liberal interpretation of the VDI guidelines can significantly improve accuracy characterisation and suggest ways in which to mitigate this problem.
We propose a series of stringent tests and revised definitions, in the same vein as VDI 2617 and similar US standards, to clarify the accuracy characterisation process. The revised methodology includes modified acceptance and reverification tests which aim to accommodate emerging technologies, laser scanning devices in particular, while maintaining the spirit of the existing and established standards. We seek to supply robust re-definitions for the accepted terms âzero pointâ and âuseful arm lengthâ, pre-supposing nothing about the geometry of the measuring device.
We also identify a source of error unique to robotised AACMMs employing laser scanners â the forward-reverse pass error. We show how eliminating this error significantly improves the repeatability of a device and propose a novel approach to the testing of probing error based on statistical uncertainty
Detection of Vibrationally Excited CO in IRC+10216
Using the Submillimeter Array we have detected the J=3-2 and 2-1 rotational
transitions from within the first vibrationally excited state of CO toward the
extreme carbon star IRC+10216 (CW Leo). The emission remains spatially
unresolved with an angular resolution of ~2" and, given that the lines
originate from energy levels that are ~3100 K above the ground state, almost
certainly originates from a much smaller (~10^{14} cm) sized region close to
the stellar photosphere. Thermal excitation of the lines requires a gas density
of ~10^{9} cm^{-3}, about an order of magnitude higher than the expected gas
density based previous infrared observations and models of the inner dust shell
of IRC+10216.Comment: Accepted for publication in ApJ Letter
Measuring nickel masses in Type Ia supernovae using cobalt emission in nebular phase spectra
The light curves of Type Ia supernovae (SNe Ia) are powered by the
radioactive decay of Ni to Co at early times, and the decay of
Co to Fe from ~60 days after explosion. We examine the evolution
of the [Co III] 5892 A emission complex during the nebular phase for SNe Ia
with multiple nebular spectra and show that the line flux follows the square of
the mass of Co as a function of time. This result indicates both
efficient local energy deposition from positrons produced in Co decay,
and long-term stability of the ionization state of the nebula. We compile 77
nebular spectra of 25 SN Ia from the literature and present 17 new nebular
spectra of 7 SNe Ia, including SN2014J. From these we measure the flux in the
[Co III] 5892 A line and remove its well-behaved time dependence to infer the
initial mass of Ni () produced in the explosion. We then examine
Ni yields for different SN Ia ejected masses ( - calculated
using the relation between light curve width and ejected mass) and find the
Ni masses of SNe Ia fall into two regimes: for narrow light curves (low
stretch s~0.7-0.9), is clustered near ~ 0.4 and
shows a shallow increase as increases from ~1-1.4; at high
stretch, clusters at the Chandrasekhar mass (1.4) while
spans a broad range from 0.6-1.2. This could constitute
evidence for two distinct SN Ia explosion mechanisms.Comment: 16 pages, 12 figures (main text), plus data tables in appendix.
Spectra released on WISeREP. Submitted to MNRAS, comments welcom
Large scale enzyme based xenobiotic identification for exposomics.
Advances in genomics have revealed many of the genetic underpinnings of human disease, but exposomics methods are currently inadequate to obtain a similar level of understanding of environmental contributions to human disease. Exposomics methods are limited by low abundance of xenobiotic metabolites and lack of authentic standards, which precludes identification using solely mass spectrometry-based criteria. Here, we develop and validate a method for enzymatic generation of xenobiotic metabolites for use with high-resolution mass spectrometry (HRMS) for chemical identification. Generated xenobiotic metabolites were used to confirm identities of respective metabolites in mice and human samples based upon accurate mass, retention time and co-occurrence with related xenobiotic metabolites. The results establish a generally applicable enzyme-based identification (EBI) for mass spectrometry identification of xenobiotic metabolites and could complement existing criteria for chemical identification
Submillimeter narrow emission lines from the inner envelope of IRC+10216
A spectral-line survey of IRC+10216 in the 345 GHz band has been undertaken
with the Submillimeter Array. Although not yet completed, it has already
yielded a fairly large sample of narrow molecular emission lines with
line-widths indicating expansion velocities of ~4 km/s, less than 3 times the
well-known value of the terminal expansion velocity (14.5 km/s) of the outer
envelope. Five of these narrow lines have now been identified as rotational
transitions in vibrationally excited states of previously detected molecules:
the v=1, J=17--16 and J=19--18 lines of Si34S and 29SiS and the v=2, J=7--6
line of CS. Maps of these lines show that the emission is confined to a region
within ~60 AU of the star, indicating that the narrow-line emission is probing
the region of dust-formation where the stellar wind is still being accelerated.Comment: 5 pages, 5 figures, Accepted for publication in Ap
Neutralino Dark Matter in Mirage Mediation
We study the phenomenology of neutralino dark matter (DM) in mirage mediation
scenario of supersymmetry breaking which results from the moduli stabilization
in some string/brane models. Depending upon the model parameters, especially
the anomaly to modulus mediation ratio determined by the moduli stabilization
mechanism, the nature of the lightest supersymmetric particle (LSP) changes
from Bino-like neutralino to Higgsino-like one via Bino-Higgsino mixing region.
For the Bino-like LSP, the standard thermal production mechanism can give a
right amount of relic DM density through the stop/stau-neutralino
coannihilation or the pseudo-scalar Higgs resonance process. We also examine
the prospect of direct and indirect DM detection in various parameter regions
of mirage mediation. Neutralino DM in galactic halo might be detected by near
future direct detection experiments in the case of Bino-Higgsino mixed LSP. The
gamma ray flux from Galactic Center might be detectable also if the DM density
profile takes a cuspy shape.Comment: One reference adde
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