40,607 research outputs found
Microstructure, magneto-transport and magnetic properties of Gd-doped magnetron-sputtered amorphous carbon
The magnetic rare earth element gadolinium (Gd) was doped into thin films of
amorphous carbon (hydrogenated \textit{a}-C:H, or hydrogen-free \textit{a}-C)
using magnetron co-sputtering. The Gd acted as a magnetic as well as an
electrical dopant, resulting in an enormous negative magnetoresistance below a
temperature (). Hydrogen was introduced to control the amorphous carbon
bonding structure. High-resolution electron microscopy, ion-beam analysis and
Raman spectroscopy were used to characterize the influence of Gd doping on the
\textit{a-}GdC(:H) film morphology, composition, density and
bonding. The films were largely amorphous and homogeneous up to =22.0 at.%.
As the Gd doping increased, the -bonded carbon atoms evolved from
carbon chains to 6-member graphitic rings. Incorporation of H opened up the
graphitic rings and stabilized a -rich carbon-chain random network. The
transport properties not only depended on Gd doping, but were also very
sensitive to the ordering. Magnetic properties, such as the spin-glass
freezing temperature and susceptibility, scaled with the Gd concentration.Comment: 9 figure
Alignment based Network Coding for Two-Unicast-Z Networks
In this paper, we study the wireline two-unicast-Z communication network over
directed acyclic graphs. The two-unicast-Z network is a two-unicast network
where the destination intending to decode the second message has apriori side
information of the first message. We make three contributions in this paper:
1. We describe a new linear network coding algorithm for two-unicast-Z
networks over directed acyclic graphs. Our approach includes the idea of
interference alignment as one of its key ingredients. For graphs of a bounded
degree, our algorithm has linear complexity in terms of the number of vertices,
and polynomial complexity in terms of the number of edges.
2. We prove that our algorithm achieves the rate-pair (1, 1) whenever it is
feasible in the network. Our proof serves as an alternative, albeit restricted
to two-unicast-Z networks over directed acyclic graphs, to an earlier result of
Wang et al. which studied necessary and sufficient conditions for feasibility
of the rate pair (1, 1) in two-unicast networks.
3. We provide a new proof of the classical max-flow min-cut theorem for
directed acyclic graphs.Comment: The paper is an extended version of our earlier paper at ITW 201
The capability enhancement of aluminium casting process by application of the novel CRIMSON method
The conventional foundry not only frequently uses batch melting, where the aluminium
alloys are melted and held in a furnace for long time, sometimes as long as a complete shift,
but also uses the gravity sand casting process where the molten aluminium alloys are
transferred using a ladle from furnace to pour station and are poured into a mould. During the
filling of the mould, the turbulent nature of the liquid metal gives rise to massive entrainment
of the surface oxide films which are the subsequently trapped into the liquid and act as micro
cracks. Also the long exposure time of the liquid surface to the surrounding environment
during melting, transferring and filling will increase the level of hydrogen absorption from
the atmosphere. The abovementioned factors are often the main reasons for casting defect
generation. In this paper the novel CRIMSON aluminium casting method is introduced which
has a number of advantages. Instead of gravity filling method, it uses the single shot upcasting
method to realize the rapid melting and rapid counter-gravity-filling mould operations
which reduce the contact time between the melt and environment thus reducing the
possibility of defect generation. Another advantage is the drastic reduction of energy
consumption due to shortened melting and filling time. A simulation software, FLOW-3D, is
used to compare this new method with the conventional gravity casting process. A tensile bar
case is used as a sample to simulate the filling process
The improvement of aluminium casting process control by application of the new CRIMSON process
All The traditional foundry usually not only uses batch melting where the
aluminium alloys are melted and held in a furnace for long time, but also uses
the gravity filling method in both Sand Casting Process (SCP) and Investment
Casting Process (ICP). In the gravity filling operation, the turbulent behaviour
of the liquid metal causes substantial entrainment of the surface oxide films
which are subsequently trapped into the liquid and generate micro cracks and
casting defects. In this paper a new CRIMSON process is introduced which
features instead of gravity filling method, using the single shot up-casting
method to realize the rapid melting and rapid filling mould operations which
reduce the contact time between the melt and environment thus reducing the
possibility of defect generation. Another advantage of the new process is the
drastic reduction of energy consumption due to shortened melting and filling
time. Two types of casting samples from SCP and ICP were compared with the new
process. The commercial software was used to simulate the filling and
solidification processes of the casting samples. The results show that the new
process has a more improved behaviour during filling a mould and solidification
than the two conventional casting processes
Integrable dispersionless KdV hierarchy with sources
An integrable dispersionless KdV hierarchy with sources (dKdVHWS) is derived.
Lax pair equations and bi-Hamiltonian formulation for dKdVHWS are formulated.
Hodograph solution for the dispersionless KdV equation with sources (dKdVWS) is
obtained via hodograph transformation. Furthermore, the dispersionless
Gelfand-Dickey hierarchy with sources (dGDHWS) is presented.Comment: 15 pages, to be published in J. Phys. A: Math. Ge
Ab Initio Simulation of the Nodal Surfaces of Heisenberg Antiferromagnets
The spin-half Heisenberg antiferromagnet (HAF) on the square and triangular
lattices is studied using the coupled cluster method (CCM) technique of quantum
many-body theory. The phase relations between different expansion coefficients
of the ground-state wave function in an Ising basis for the square lattice HAF
is exactly known via the Marshall-Peierls sign rule, although no equivalent
sign rule has yet been obtained for the triangular lattice HAF. Here the CCM is
used to give accurate estimates for the Ising-expansion coefficients for these
systems, and CCM results are noted to be fully consistent with the
Marshall-Peierls sign rule for the square lattice case. For the triangular
lattice HAF, a heuristic rule is presented which fits our CCM results for the
Ising-expansion coefficients of states which correspond to two-body excitations
with respect to the reference state. It is also seen that Ising-expansion
coefficients which describe localised, -body excitations with respect to the
reference state are found to be highly converged, and from this result we infer
that the nodal surface of the triangular lattice HAF is being accurately
modeled. Using these results, we are able to make suggestions regarding
possible extensions of existing quantum Monte Carlo simulations for the
triangular lattice HAF.Comment: 24 pages, Latex, 3 postscript figure
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