674 research outputs found
Alloys-by-design:A low-modulus titanium alloy for additively manufactured biomedical implants
The performance of many metal biomedical implants – such as fusion cages for spines – is inherently limited by the mismatch of mechanical properties between the metal and the biological bone tissue it promotes. Here, an alloy design approach is used to isolate titanium alloy compositions for biocompatibility which exhibit a modulus of elasticity lower than the Ti-6Al-4V grade commonly employed for this application. Due to the interest in alloys for personalised medicine, additive manufacturability is also considered: compositions with low cracking susceptibility and with propensity for non-planar growth are identified. An optimal alloy composition is selected for selective laser melting, and its processability and mechanical properties tested. Additive manufacturing is used to engineer an heterogeneous microstructure with outstanding combined strength and ductility. Our results confirm the suitability of novel titanium alloys for lowering the stiffness towards that needed whilst being additively manufacturable and strong
Alloys-by-design:A low-modulus titanium alloy for additively manufactured biomedical implants
The performance of many metal biomedical implants – such as fusion cages for spines – is inherently limited by the mismatch of mechanical properties between the metal and the biological bone tissue it promotes. Here, an alloy design approach is used to isolate titanium alloy compositions for biocompatibility which exhibit a modulus of elasticity lower than the Ti-6Al-4V grade commonly employed for this application. Due to the interest in alloys for personalised medicine, additive manufacturability is also considered: compositions with low cracking susceptibility and with propensity for non-planar growth are identified. An optimal alloy composition is selected for selective laser melting, and its processability and mechanical properties tested. Additive manufacturing is used to engineer an heterogeneous microstructure with outstanding combined strength and ductility. Our results confirm the suitability of novel titanium alloys for lowering the stiffness towards that needed whilst being additively manufacturable and strong
X-ray measurement of residual stresses in laser surface melted Ti-6Al-4V alloy
In this paper, we report on the residual stresses in laser surface melted Ti-6Al-4V, determined using X-ray diffraction methods. The principal result is that there is an increase in the transverse residual stress with each successive, overlapping laser track. The result can be used to explain the observation of crack formation in overlapping tracks but not necessarily in single tracks produced under identical processing conditions.
Regularized overlap and the chiral determinant
We study the relationship between the continuum overlap and its corresponding
chiral determinant, showing that the former amounts to an unregularised version
of the latter. We then construct a regularised continuum overlap, and consider
the chiral anomalies that follow therefrom. The relation between these
anomalies and the ones derived from the formal (i.e., unregularised) overlap is
elucidated.Comment: 14 pages, late
Various spin-polarization states beyond the maximum-density droplet: a quantum Monte Carlo study
Using variational quantum Monte Carlo method, the effect of Landau-level
mixing on the lowest-energy--state diagram of small quantum dots is studied in
the magnetic field range where the density of magnetic flux quanta just exceeds
the density of electrons. An accurate analytical many-body wave function is
constructed for various angular momentum and spin states in the lowest Landau
level, and Landau-level mixing is then introduced using a Jastrow factor. The
effect of higher Landau levels is shown to be significant; the transition lines
are shifted considerably towards higher values of magnetic field and certain
lowest-energy states vanish altogether.Comment: 4 pages, 2 figures. Submitted to Phys. Rev.
Eigenvalue estimates for non-selfadjoint Dirac operators on the real line
We show that the non-embedded eigenvalues of the Dirac operator on the real
line with non-Hermitian potential lie in the disjoint union of two disks in
the right and left half plane, respectively, provided that the of
is bounded from above by the speed of light times the reduced Planck
constant. An analogous result for the Schr\"odinger operator, originally proved
by Abramov, Aslanyan and Davies, emerges in the nonrelativistic limit. For
massless Dirac operators, the condition on implies the absence of nonreal
eigenvalues. Our results are further generalized to potentials with slower
decay at infinity. As an application, we determine bounds on resonances and
embedded eigenvalues of Dirac operators with Hermitian dilation-analytic
potentials
On the Resolution of the Time-Like Singularities in Reissner-Nordstrom and Negative-Mass Schwarzschild
Certain time-like singularities are shown to be resolved already in classical
General Relativity once one passes from particle probes to scalar waves. The
time evolution can be defined uniquely and some general conditions for that are
formulated. The Reissner-Nordstrom singularity allows for communication through
the singularity and can be termed "beam splitter" since the transmission
probability of a suitably prepared high energy wave packet is 25%. The high
frequency dependence of the cross section is w^{-4/3}. However, smooth
geometries arbitrarily close to the singular one require a finite amount of
negative energy matter. The negative-mass Schwarzschild has a qualitatively
different resolution interpreted to be fully reflecting. These 4d results are
similar to the 2d black hole and are generalized to an arbitrary dimension d>4.Comment: 47 pages, 5 figures. v2: See end of introduction for an important
note adde
Composite Fermion Description of Correlated Electrons in Quantum Dots: Low Zeeman Energy Limit
We study the applicability of composite fermion theory to electrons in
two-dimensional parabolically-confined quantum dots in a strong perpendicular
magnetic field in the limit of low Zeeman energy. The non-interacting composite
fermion spectrum correctly specifies the primary features of this system.
Additional features are relatively small, indicating that the residual
interaction between the composite fermions is weak. \footnote{Published in
Phys. Rev. B {\bf 52}, 2798 (1995).}Comment: 15 pages, 7 postscript figure
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