13,968 research outputs found
Jets associated with Z^0 boson production in heavy-ion collisions at the LHC
The heavy ion program at the LHC will present unprecedented opportunities to
probe hot QCD matter, that is, the quark gluon plasma (QGP). Among these
exciting new probes are high energy partons associated with the production of a
Z^0 boson, or Z^0 tagged jets. Once produced, Z^0 bosons are essentially
unaffected by the strongly interacting medium produced in heavy-ion collisions,
and therefore provide a powerful signal of the initial partonic energy and
subsequent medium induced partonic energy loss. When compared with theory,
experimental measurements of Z^0 tagged jets will help quantify the jet
quenching properties of the QGP and discriminate between different partonic
energy loss formalisms. In what follows, I discuss the advantages of tagged
jets over leading particles, and present preliminary results of the production
and suppression of Z^0 tagged jets in relativistic heavy-ion collisions at LHC
energies using the Guylassy-Levai-Vitev (GLV) partonic energy loss formalism.Comment: To appear in the proceedings of the 2010 Winter Workshop on Nuclear
Dynamics, which was held in Ocho Rios, Jamaica, mon
Cracks Cleave Crystals
The problem of finding what direction cracks should move is not completely
solved. A commonly accepted way to predict crack directions is by computing the
density of elastic potential energy stored well away from the crack tip, and
finding a direction of crack motion to maximize the consumption of this energy.
I provide here a specific case where this rule fails. The example is of a crack
in a crystal. It fractures along a crystal plane, rather than in the direction
normally predicted to release the most energy. Thus, a correct equation of
motion for brittle cracks must take into account both energy flows that are
described in conventional continuum theories and details of the environment
near the tip that are not.Comment: 6 page
Collective patterns arising out of spatio-temporal chaos
We present a simple mathematical model in which a time averaged pattern
emerges out of spatio-temporal chaos as a result of the collective action of
chaotic fluctuations. Our evolution equation possesses spatial translational
symmetry under a periodic boundary condition. Thus the spatial inhomogeneity of
the statistical state arises through a spontaneous symmetry breaking. The
transition from a state of homogeneous spatio-temporal chaos to one exhibiting
spatial order is explained by introducing a collective viscosity which relates
the averaged pattern with a correlation of the fluctuations.Comment: 11 pages (Revtex) + 5 figures (postscript
Experimental Signatures of Critically Balanced Turbulence in MAST
Beam Emission Spectroscopy (BES) measurements of ion-scale density
fluctuations in the MAST tokamak are used to show that the turbulence
correlation time, the drift time associated with ion temperature or density
gradients, the particle (ion) streaming time along the magnetic field and the
magnetic drift time are consistently comparable, suggesting a "critically
balanced" turbulence determined by the local equilibrium. The resulting
scalings of the poloidal and radial correlation lengths are derived and tested.
The nonlinear time inferred from the density fluctuations is longer than the
other times; its ratio to the correlation time scales as
, where ion collision rate/streaming rate.
This is consistent with turbulent decorrelation being controlled by a zonal
component, invisible to the BES, with an amplitude exceeding the drift waves'
by .Comment: 6 pages, 4 figures, submitted to PR
Quantum dot dephasing by edge states
We calculate the dephasing rate of an electron state in a pinched quantum
dot, due to Coulomb interactions between the electron in the dot and electrons
in a nearby voltage biased ballistic nanostructure. The dephasing is caused by
nonequilibrium time fluctuations of the electron density in the nanostructure,
which create random electric fields in the dot. As a result, the electron level
in the dot fluctuates in time, and the coherent part of the resonant
transmission through the dot is suppressed
Dimensionless Measures of Turbulent Magnetohydrodynamic Dissipation Rates
The magnetic Reynolds number R_M, is defined as the product of a
characteristic scale and associated flow speed divided by the microphysical
magnetic diffusivity. For laminar flows, R_M also approximates the ratio of
advective to dissipative terms in the total magnetic energy equation, but for
turbulent flows this latter ratio depends on the energy spectra and approaches
unity in a steady state. To generalize for flows of arbitrary spectra we define
an effective magnetic dissipation number, R_{M,e}, as the ratio of the
advection to microphysical dissipation terms in the total magnetic energy
equation, incorporating the full spectrum of scales, arbitrary magnetic Prandtl
numbers, and distinct pairs of inner and outer scales for magnetic and kinetic
spectra. As expected, for a substantial parameter range R_{M,e}\sim {O}(1) <<
R_M. We also distinguish R_{M,e} from {\tilde R}_{M,e} where the latter is an
effective magnetic Reynolds number for the mean magnetic field equation when a
turbulent diffusivity is explicitly imposed as a closure. That R_{M,e} and
{\tilde R}_{M,e} approach unity even if R_M>>1 highlights that, just as in
hydrodynamic turbulence,energy dissipation of large scale structures in
turbulent flows via a cascade can be much faster than the dissipation of large
scale structures in laminar flows. This illustrates that the rate of energy
dissipation by magnetic reconnection is much faster in turbulent flows, and
much less sensitive to microphysical reconnection rates compared to laminar
flows.Comment: 14 pages (including 2 figs), accepted by MNRA
Learning through social spaces: migrant women and lifelong learning in post-colonial London
This article shows how migrant women engage in learning through social spaces. It argues that such spaces are little recognised, and that there are multiple ways in which migrant women construct and negotiate their informal learning through socialising with other women in different informal modes. Additionally, the article shows how learning is shaped by the socio-political, geographical and multicultural context of living in London, outlining ways in which gendered and racialised identities shape, construct and constrain participation in lifelong learning. The article shows that one way in which migrant women resist (post)colonial constructions of difference is by engaging in informal and non-formal lifelong learning, arguing that the benefits are (at least) two-fold. The women develop skills (including language skills) but also use their informal learning to develop what is referred to in this article as 'relational capital'. The article concludes that informal lifelong learning developed through social spaces can enhance a sense of belonging for migrant women
Reâdefining the virtual reality dental simulator: Demonstrating concurrent validity of clinically relevant assessment and feedback
Introduction
Virtual reality (VR) dental simulators are gaining momentum as a useful tool to educate dental students. To date, no VR dental simulator exercise has been designed which is capable of reliably providing validated, meaningful clinical feedback to dental students. This study aims to measure the concurrent validity of the assessment, and the provision of qualitative feedback, pertaining to cavity preparations by VR dental simulators.
Methods
A cavity preparation exercise was created on a VR dental simulator, and assessment criteria for cavity preparations were developed. The exercise was performed 10 times in order to demonstrate a range of performances and for each, the simulator feedback was recorded. The exercises were subsequently threeâdimensionally printed and 12 clinical teachers were asked to assess the preparations according to the same criteria. Interârater reliability (IRR) between clinical teachers was measured using a freeâmarginal multirater kappa value. Clinical teacher assessment responses were compared with the VR simulator responses and percentage agreements calculated.
Results
IRR values for each exercise ranged from 0.39â0.77 (69.39â88.48%). The assessment of smoothness (Îșfree0.58, 78.79%) and ability to follow the outline (Îșfree0.56, 77.88%) demonstrated highest agreement between clinical teachers, whilst the assessment of undercut (Îșfree0.15, 57.58%) and depth (Îșfree 0.28, 64.09%) had the lowest agreement. The modal percentage agreement between clinical teachers and the VR simulator was, on average, 78% across all exercises.
Conclusion
The results of this study demonstrate that it is possible to provide reliable and clinically relevant qualitative feedback via a VR dental simulator. Further research should look to employ this technique across a broader range of exercises that help to develop other complex operative dental skills
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