7,814 research outputs found
Decolonizing the Curriculum and the University:A Panel Discussion with Rolando Vasquez, Layal Ftouni and Toni Pape, 31 March 2021
This panel was made possible by the collaborative efforts of editors of Junctions and an intern from Transmission in Motion, both spaces being initiatives by Utrecht University. While emerging from independent curiosities around decolonial thought and practice, specifically related to the movement in the educational sector (more commonly recognised as Decolonizing the Curriculum, a subset of Decolonizing the University movement) this collaborative panel aims to have as starting point the ideology, better articulated Walter D. Mignolo and Catherine E. Walsh, as a relational practise which requires the recognition of one’s position as their entry point. In their words (2018), decolonial thinking and practice embodies (or should embody) situatedness, “…the ways that different local histories and embodied conceptions and practices of decoloniality, including our own, can enter into conversations and build understandings that both cross geopolitical locations and colonial differences and contest the totalizing claims and political-epistemic violence of modernity” (Walsh and Mignolo 2018, 1). We understand this as a way to contextualise decolonial theory and practice within educational spaces in the Netherlands, so as not to risk transforming it into an empty metaphor. To contextualise theory and practice also requires an understanding of how Decolonial Work is spoken about and practised in specific institutional spaces. With that in mind, we invited Layal Ftouni, Toni Pape and Rolando Vazquez Melken to discuss the limits of what we allow ourselves to think, talk, imagine, make and do in relation to the discourse of decolonization
Time and duration of chondrule formation: Constraints from 26Al-26Mg ages of individual chondrules
Chondrules from unequilibrated ordinary and carbonaceous chondrites belong to the oldest and most primitive materials from the early solar system and record chemical and isotopic signatures relating to their formation and evolution. These signatures allow tracing protoplanetary disk processes that eventually led to the formation of planetary building blocks and rocky planets. 26Al-26Mg ages based on mineral-mesostasis isochrons of 31 porphyritic ferromagnesian chondrules, that belong mainly to type-II, constrain the time of chondrule melting prior to incorporation into the respective chondrite parent bodies. For this study chondrules from the unequilibrated L, L(LL) and LL ordinary chondrites (UOCs) NWA 5206, NWA 8276, MET 96503, MET 00452, MET 00526, NWA 7936 and QUE 97008 were selected, which are of petrologic types 3.00-3.15 and were thus least metamorphosed after formation. Magnesium and Al isotopes were measured in-situ by Secondary Ion Mass Spectrometry (SIMS) using a CAMECA 1280 ims. 26Mg excess from in-situ decay of 26Al correlating with 27Al/24Mg has been detected in the mesostasis of all but one chondrule. The initial Al isotopic compositions (26Al/27Al)0 and 26Mg/24Mg ratios (d26Mg*0) deduced from internal mineral isochron regressions range from (9.5 ± 2.8) × 10-6 to (3.1 ± 1.2) × 10-6 and -0.020 ± 0.028‰ to 0.011 ± 0.039‰, respectively. The corresponding chondrule ages (∆tCAI), calculated relative to calcium-aluminum-rich inclusions (CAIs) using the canonical 26Al/27Al = (5.23 ± 0.13) × 10-5, are between 1.76_(-0.27)^(+0.36) and 2.92_(-0.34)^(+0.51) Ma and date the melt formation and thus primary chondrule formation from dust-like precursors or reprocessing of older chondrules. The age range agrees with those acquired with different short-lived chronometers and with published 26Al-26Mg ages, the majority of which were obtained for chondrules from the Bishunpur and Semarkona meteorites, although no chondrule with (26Al/27Al)0 > 10-5 was found. Chondrules in single chondrite samples or between different chondrite groups show no distinct age distributions. The initial 26Al/27Al of the oldest chondrules in the L(LL)/LL and L chondrite samples are identical within their 1σ uncertainties and yield a mean age of 1.99_(-0.08)^(+0.08) Ma and 1.81_(-0.10)^(+0.11) Ma, respectively. The oldest chondrules from six of the seven studied samples record a mean age of 1.94_(-0.06)^(+0.07) Ma. Since heating events in the protoplanetary disk could have partially reset the Al-Mg systematics in pre-existing chondrules and this would have shifted recorded 26Al-26Mg ages toward younger dates, the oldest mean age of 1.81_(-0.10)^(+0.11) Ma recorded in L chondrite chondrules is interpreted to date the rapid and punctuated onset of chondrule formation. The density distribution of chondrule ages from this study, which comprises the largest single dataset of OC chondrule ages, combined with published ages for chondrules from ordinary and carbonaceous chondrites reveals major age peaks for OC chondrules at 2.0 and 2.3 Ma. Chondrules in ordinary and carbonaceous chondrites formed almost contemporaneously (with a possible distinction between CC groups) in two chemically distinct reservoirs, probably in density-enriched regions at the edges of Jupiter’s orbit. The young formation ages of chondrules suggest that they do not represent precursors but rather by-products of planetesimal accretion
Process design for 5-axis ball end milling using a real-time capable dynamic material removal simulation
For repairing turbine blades or die and mold forms, additive manufacturing processes are commonly used to build-up new material to damaged sections. Afterwards, a subsequent re-contouring process such as 5-axis ball end milling is required to remove the excess material restoring the often complex original geometries. The process design of the re-contouring operation has to be done virtually, because the individuality of the repair cases prevents actual running-in processes. Hard-to-cut materials e.g. titanium or nickel alloys, parts prone to vibration and long tool holders complicate the repair even further. Thus, a fast and flexible material removal simulation is needed. The simulation has to predict suitable processes focusing shape deviations under consideration of process stability for arbitrary complex engagement conditions. In this paper, a dynamic multi-dexel based material removal simulation is presented, which is able to predict high-resolution surface topography and stable parameters for arbitrary processes such as 5-axis ball end milling. In contrast to other works, the simulation is able to simulate an unstable process using discrete cutting edges in real-time. © 2020, The Author(s)
The Sensitivity of Auditory-Motor Representations to Subtle Changes in Auditory Feedback While Singing
Singing requires accurate control of the fundamental frequency (F0) of the voice. This study examined trained singers’ and untrained singers’ (nonsingers’) sensitivity to subtle manipulations in auditory feedback and the subsequent effect on the mapping between F0 feedback and vocal control. Participants produced the consonant-vowel /ta/ while receiving auditory feedback that was shifted up and down in frequency. Results showed that singers and nonsingers compensated to a similar degree when presented with frequency-altered feedback (FAF); however, singers’ F0 values were consistently closer to the intended pitch target. Moreover, singers initiated their compensatory responses when auditory feedback was shifted up or down 6 cents or more, compared to nonsingers who began compensating when feedback was shifted up 26 cents and down 22 cents. Additionally, examination of the first 50 ms of vocalization indicated that participants commenced subsequent vocal utterances, during FAF, near the F0 value on previous shift trials. Interestingly, nonsingers commenced F0 productions below the pitch target and increased their F0 until they matched the note. Thus, singers and nonsingers rely on an internal model to regulate voice F0, but singers’ models appear to be more sensitive in response to subtle discrepancies in auditory feedback
ICP-SFMS search for long-lived naturally-occurring heavy, superheavy and superactinide nuclei compared to AMS experiments
Negative results obtained in AMS searches by Dellinger et al. on mostly
unrefined ores have led them to conclude that the very heavy long-lived species
found in chemically processed samples with ICP-SFMS by Marinov et al. are
artifacts. We argue that it may not be surprising that results obtained from
small random samplings of inhomogeneous natural minerals would contrast with
concentrations found in homogeneous materials extracted from large quantities
of ore. We also point out that it is possible that the groups of counts at
masses 296 and 294 seen by Dellinger et al. could be, within experimental
uncertainties, due to Rg and eka-Bi in long-lived isomeric
states. In such case, the experiments of Dellinger et al. lend support to the
experiments of Marinov et al.Comment: 2 pages. Accepted for publication in Int. J. Mod. Phys.
Existence of long-lived isotopes of a superheavy element in natural Au
Evidence for the existence of long-lived isotopes with atomic mass numbers
261 and 265 and abundance of (1-10)x10 relative to Au has been found in
a study of natural Au using an inductively coupled plasma - sector field mass
spectrometer. The measured masses fit the predictions made for the masses of
Rg and Rg (Z=111) and for some isotopes of nearby elements.
The possibility that these isotopes belong to the recently discovered class
of long-lived high spin super- and hyperdeformed isomeric states is discussed.Comment: 4 pages, 3 figures, 2 table
Updated Post-WMAP Benchmarks for Supersymmetry
We update a previously-proposed set of supersymmetric benchmark scenarios,
taking into account the precise constraints on the cold dark matter density
obtained by combining WMAP and other cosmological data, as well as the LEP and
b -> s gamma constraints. We assume that R parity is conserved and work within
the constrained MSSM (CMSSM) with universal soft supersymmetry-breaking scalar
and gaugino masses m_0 and m_1/2. In most cases, the relic density calculated
for the previous benchmarks may be brought within the WMAP range by reducing
slightly m_0, but in two cases more substantial changes in m_0 and m_1/2 are
made. Since the WMAP constraint reduces the effective dimensionality of the
CMSSM parameter space, one may study phenomenology along `WMAP lines' in the
(m_1/2, m_0) plane that have acceptable amounts of dark matter. We discuss the
production, decays and detectability of sparticles along these lines, at the
LHC and at linear e+ e- colliders in the sub- and multi-TeV ranges, stressing
the complementarity of hadron and lepton colliders, and with particular
emphasis on the neutralino sector. Finally, we preview the accuracy with which
one might be able to predict the density of supersymmetric cold dark matter
using collider measurements.Comment: 43 pages LaTeX, 13 eps figure
An open environment for development of manufacturing applications on vf-OS
Innovative methodologies for development promote strong involvement of the development community and the developers' engagement. This chapter describes a novel environment that was envisioned for this purpose, involved in the scope of the H2020 European Project virtual factory Open Operating System (vf‐OS). The purpose of the H2020 vf‐OS European Project is to provide manufacturing businesses with an open Operating System that will allow them to create, develop, build and load applications that span and cover the whole manufacturing operation and process. The vf‐OAK software development kit (SDK) is a centralized environment for the development of applications and, generically, for centralized access to the vf‐OS assets and functionalities. The SDK for vApps has a process interpreter which can transform the results from the Process Designer tool to JavaScript language. The vf‐OS System Dashboard is a runtime, central dashboard and task manager, aimed at monitoring, warning, configuring, and adapting system resources.info:eu-repo/semantics/acceptedVersio
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