102,702 research outputs found
Narrative in design development
This paper describes the value of narrative used with ideation tools in aiding the rapid production of product concepts and designs for masters students of graphics, fine art, product and industrial design. The ideation tools used alongside narrative included elements of divergent and convergent thinking in combination with reverse engineering and functional analysis, and practical prototyping using a range of readily adapted artefacts. Narrative was introduced and used by the students in order to ensure the development of a context and purpose for the product, artefact or system developed or proposed and to stimulate original product concepts, ideas and thinking. The concept of narrative is familiar in design. Here however the concept was reinforced using structures associated with fictional narrative. Reverse engineering exploring the deconstruction and identification of function for each component in a product was used to aid students ensure practicality in their idea implementation. This paper describes positive experiences resulting from this activity, with a particular focus on the value of narrative in developing robust concepts. The use of physical prototyping provided tangible and instant feedback for divergent and convergent phases of idea development
Nonsymmorphic symmetry-required band crossings in topological semimetals
We show that for two-band systems nonsymmorphic symmetries may enforce the
existence of band crossings in the bulk, which realize Fermi surfaces of
reduced dimensionality. We find that these unavoidable crossings originate from
the momentum dependence of the nonsymmorphic symmetry, which puts strong
restrictions on the global structure of the band configurations. Three
different types of nonsymmorphic symmetries are considered: (i) a unitary
nonsymmorphic symmetry, (ii) a nonsymmorphic magnetic symmetry, and (iii) a
nonsymmorphic symmetry combined with inversion. For nonsymmorphic symmetries of
the latter two types, the band crossings are located at high-symmetry points of
the Brillouin zone, with their exact positions being determined by the algebra
of the symmetry operators. To characterize these band degeneracies we introduce
a \emph{global} topological charge and show that it is of type,
which is in contrast to the \emph{local} topological charge of Fermi points in,
say, Weyl semimetals. To illustrate these concepts, we discuss the -flux
state as well as the SSH model at its critical point and show that these two
models fit nicely into our general framework of nonsymmorphic two-band systems.Comment: 6.5 pages, 4 figure
Accurate Modelling of Left-Handed Metamaterials Using Finite-Difference Time-Domain Method with Spatial Averaging at the Boundaries
The accuracy of finite-difference time-domain (FDTD) modelling of left-handed
metamaterials (LHMs) is dramatically improved by using an averaging technique
along the boundaries of LHM slabs. The material frequency dispersion of LHMs is
taken into account using auxiliary differential equation (ADE) based dispersive
FDTD methods. The dispersive FDTD method with averaged permittivity along the
material boundaries is implemented for a two-dimensional (2-D) transverse
electric (TE) case. A mismatch between analytical and numerical material
parameters (e.g. permittivity and permeability) introduced by the time
discretisation in FDTD is demonstrated. The expression of numerical
permittivity is formulated and it is suggested to use corrected permittivity in
FDTD simulations in order to model LHM slabs with their desired parameters. The
influence of switching time of source on the oscillation of field intensity is
analysed. It is shown that there exists an optimum value which leads to fast
convergence in simulations.Comment: 17 pages, 7 figures, submitted to Journal of Optics A Nanometa
special issu
Analytical considerations of flow boiling heat transfer in metal-foam filled tubes
Flow boiling in metal-foam filled tube was analytically investigated based on a modified microstructure model, an original boiling heat transfer model and fin analysis for metal foams. Microstructure model of metal foams was established, by which fiber diameter and surface area density were precisely predicted. The heat transfer model for flow boiling in metal foams was based on annular pattern, in which two phase fluid was composed by vapor region in the center of the tube and liquid region near the wall. However, it was assumed that nucleate boiling performed only in the liquid region. Fin analysis and heat transfer network for metal foams were integrated to obtain the convective heat transfer coefficient at interface. The analytical solution was verified by its good agreement with experimental data. The parametric study on heat transfer coefficient and boiling mechanism was also carried out
The non-linear evolution of bispectrum from the scale-free N-body simulation
We have accurately measured the bispectrum for four scale-free models of
structure formation with the spectral index , 0, -1, and -2. The
measurement is based on a new method that can effectively eliminate the alias
and numerical artifacts, and reliably extend the analysis into the strongly
non-linear regime. The work makes use of a set of state-of-the art N-body
simulations that have significantly increased the resolution range compared
with the previous studies on the subject. With these measured results, we
demonstrated that the measured bispectrum depends on the shape and size of
-triangle even in the strongly nonlinear regime. It increases with
wavenumber and decreases with the spectral index. These results are in contrast
with the hypothesis that the reduced bispectrum is a constant in the strongly
non-linear regime. We also show that the fitting formula of Scoccimarro &
Frieman (1999) does not describe our simulation results well (with a typical
error about 40 percent). In the end, we present a new fitting formula for the
reduced bispectrum that is valid for with a typical error of
10 percent only.Comment: 33 pages, including 1 table, 14 figures, accepted by Ap
High-quality positrons from a multi-proton bunch driven hollow plasma wakefield accelerator
By means of hollow plasma, multiple proton bunches work well in driving
nonlinear plasma wakefields and accelerate electrons to energy frontier with
preserved beam quality. However, the acceleration of positrons is different
because the accelerating structure is strongly charge dependent. There is a
discrepancy between keeping a small normalized emittance and a small energy
spread. This results from the conflict that the plasma electrons used to
provide focusing to the multiple proton bunches dilute the positron bunch. By
loading an extra electron bunch to repel the plasma electrons and meanwhile
reducing the plasma density slightly to shift the accelerating phase with a
conducive slope to the positron bunch, the positron bunch can be accelerate to
400 GeV (40% of the driver energy) with an energy spread as low as 1% and well
preserved normalized emittance. The successful generation of high quality and
high energy positrons paves the way to the future energy frontier lepton
colliders.Comment: 14 pages, 5 figure
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