1,966 research outputs found
"Se tennene!" : barnetegning - en skatt og et slags spor : en sosiokulturell analyse av barns tegneprosesser i barnehagen
Ways of talking about drawing practices
In this article, I explore how part of the culture historian professor Ernst Gombrichâs vocabulary can be used in two examples of todayâs drawing processes among children (age 9â12). His terms are related to their possible theoretical origin and placed in sociocultural understandings of human activityâand contrasted with other possible useful terms in a drawing-teaching context. How terms can encourage various teaching practices is then discusse
Police Criminal Charging Decisions: An Examination of Post-Arrest Decision-Making
Scholars have encouraged studies of police decision-making to move beyond the arrest decision into research that broadens the understanding of police behavior. The criminal charge placed by officers against offenders is largely an untouched area of study. Examining criminal charging decisions goes beyond simple dichotomous decisions, such as arrest, but instead explores the area of police leniency or punitiveness. Randomly constructed vignettes describing a domestic violence incident were given to officers from four agencies. Officers indicated the criminal charges they would likely list against an offender if they were to make an arrest. Serious criminal charges were often supported by additional, but less serious, charges. Victim injury and an uncooperative offender were related to the decision to charge a misdemeanor offense. There was a significant negative relationship between the number of charges listed and more experienced officers and officers working in smaller agencies. The implications of this study and directions for future research are discussed
Observation of Target Electron Momentum Effects in Single-Arm M\o ller Polarimetry
In 1992, L.G. Levchuk noted that the asymmetries measured in M\o ller
scattering polarimeters could be significantly affected by the intrinsic
momenta of the target electrons. This effect is largest in devices with very
small acceptance or very high resolution in laboratory scattering angle. We use
a high resolution polarimeter in the linac of the polarized SLAC Linear
Collider to study this effect. We observe that the inclusion of the effect
alters the measured beam polarization by -14% of itself and produces a result
that is consistent with measurements from a Compton polarimeter. Additionally,
the inclusion of the effect is necessary to correctly simulate the observed
shape of the two-body elastic scattering peak.Comment: 29 pages, uuencoded gzip-compressed postscript (351 kb). Uncompressed
postscript file (898 kb) available to DECNET users as
SLC::USER_DISK_SLC1:[MORRIS]levpre.p
Disordered Regimes of the one-dimensional complex Ginzburg-Landau equation
I review recent work on the ``phase diagram'' of the one-dimensional complex
Ginzburg-Landau equation for system sizes at which chaos is extensive.
Particular attention is paid to a detailed description of the spatiotemporally
disordered regimes encountered. The nature of the transition lines separating
these phases is discussed, and preliminary results are presented which aim at
evaluating the phase diagram in the infinite-size, infinite-time, thermodynamic
limit.Comment: 14 pages, LaTeX, 9 figures available by anonymous ftp to
amoco.saclay.cea.fr in directory pub/chate, or by requesting them to
[email protected]
Two-dimensional turbulence in magnetised plasmas
In an inhomogeneous magnetised plasma the transport of energy and particles
perpendicular to the magnetic field is in general mainly caused by quasi
two-dimensional turbulent fluid mixing. The physics of turbulence and structure
formation is of ubiquitous importance to every magnetically confined laboratory
plasma for experimental or industrial application. Specifically, high
temperature plasmas for fusion energy research are also dominated by the
properties of this turbulent transport. Self-organisation of turbulent vortices
to mesoscopic structures like zonal flows is related to the formation of
transport barriers that can significantly enhance the confinement of a fusion
plasma. This subject of great importance in research is rarely touched on in
introductory plasma physics or continuum dynamics courses. Here a brief
tutorial on 2D fluid and plasma turbulence is presented as an introduction to
the field, appropriate for inclusion in undergraduate and graduate courses.Comment: This is an author-created, un-copyedited version of an article
published in European Journal of Physics. IOP Publishing Ltd is not
responsible for any errors or omissions in this version of the manuscript or
any version derived from it. The definitive publisher authenticated version
is available online at doi: 10.1088/0143-0807/29/5/00
CMBPol Mission Concept Study: Foreground Science Knowledge and Prospects
We report on our knowledge of Galactic foregrounds, as well as on how a CMB
satellite mission aiming at detecting a primordial B-mode signal (CMBPol) will
contribute to improving it. We review the observational and analysis techniques
used to constrain the structure of the Galactic magnetic field, whose presence
is responsible for the polarization of Galactic emissions. Although our current
understanding of the magnetized interstellar medium is somewhat limited,
dramatic improvements in our knowledge of its properties are expected by the
time CMBPol flies. Thanks to high resolution and high sensitivity instruments
observing the whole sky at frequencies between 30 GHz and 850 GHz, CMBPol will
not only improve this picture by observing the synchrotron emission from our
galaxy, but also help constrain dust models. Polarized emission from
interstellar dust indeed dominates over any other signal in CMBPol's highest
frequency channels. Observations at these wavelengths, combined with
ground-based studies of starlight polarization, will therefore enable us to
improve our understanding of dust properties and of the mechanism(s)
responsible for the alignment of dust grains with the Galactic magnetic field.
CMBPol will also shed new light on observations that are presently not well
understood. Morphological studies of anomalous dust and synchrotron emissions
will indeed constrain their natures and properties, while searching for
fluctuations in the emission from heliospheric dust will test our understanding
of the circumheliospheric interstellar medium. Finally, acquiring more
information on the properties of extra-Galactic sources will be necessary in
order to maximize the cosmological constraints extracted from CMBPol's
observations of CMB lensing. (abridged)Comment: 43 pages, 7 figures, 2 table
Formation of CO2 on a carbonaceous surface: a quantum chemical study
The formation of CO2 in the gas phase and on a polyaromatic hydrocarbon surface (coronene) via three possible pathways is investigated with density functional theory. Calculations show that the coronene surface catalyses the formation of CO2 on model grain surfaces. The addition of O-3 to CO is activated by 2530 K in the gas phase. This barrier is lowered by 253 K for the Eley-Rideal mechanism and 952 K for the hot-atom mechanism on the surface of coronene. Alternative pathways for the formation of CO2 are the addition of O-3 to the HCO radical, followed by dissociation of the HCO2 intermediate. The O + HCO addition is barrierless in the gas phase and on the surface and is more than sufficiently exothermic to subsequently cleave the H-C bond. The third mechanism, OH + CO addition followed by H removal from the energized HOCO intermediate, has a gas-phase exit barrier that is 1160 K lower than the entrance barrier. On the coronene surface, however, both barriers are almost equal. Because the HOCO intermediate can also be stabilized by energy dissipation to the surface, it is anticipated that for the surface reaction the adsorbed HOCO could be a long-lived intermediate. In this case, the stabilized HOCO intermediate could react, in a barrierless manner, with a hydrogen atom to form H-2 + CO2, HCO2H, or H2O + CO
Automated prediction of catalytic mechanism and rate law using graph-based reaction-path sampling
In a recent article [J. Chem. Phys., 143, 094106 (2015)], we have introduced a novel graph-based sampling scheme which can be used to generate chemical reaction paths in many-atom systems in an efficient and highly-automated manner. The main goal of this work is to demonstrate how this approach, when combined with direct kinetic modelling, can be used to determine the mechanism and phenomenological rate law of a complex catalytic cycle, namely cobalt-catalyzed hydroformylation of ethene. Our graph-based sampling scheme generates 31 unique chemical products and 32 unique chemical reaction pathways; these sampled structures and reaction paths en- able automated construction of a kinetic network model of the catalytic system when combined with density functional theory (DFT) calculations of free energies and resul- tant transition-state theory rate constants. Direct simulations of this kinetic network across a range of initial reactant concentrations enables determination of both the re- action mechanism and the associated rate law in an automated fashion, without the need for either pre-supposing a mechanism or making steady-state approximations in kinetic analysis. Most importantly, we find that the reaction mechanism which emerges from these simulations is exactly that originally proposed by Heck and Breslow; fur- thermore, the simulated rate law is also consistent with previous experimental and computational studies, exhibiting a complex dependence on carbon monoxide pres- sure. While the inherent errors of using DFT simulations to model chemical reactivity limit the quantitative accuracy of our calculated rates, this work confirms that our automated simulation strategy enables direct analysis of catalytic mechanisms from first principles
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