36,777 research outputs found
Advances In Ti6Al4V Additive Manufacturing in South Africa
Published Conference ProceedingsSouth Africa has the potential to add significant value to its titanium natural resource. Initiated by a National Research and Technology Foresight Project in 1999, a national consensus has grown regarding this beneficiation opportunity. It culminated in the establishment of the Titanium Centre of Competence in 2009. Additive manufacturing was included as technology platform of the Titanium Centre of Competence. In 2013 the Department of Science and Technology commissioned the development of a South African Additive Manufacturing Technology Roadmap.
This paper elaborates on the growth of additive manufacturing in South Africa, emphasising the successes achieved with producing customised medical implants from Ti6Al4V powder. Examples of internationally leading work on such implants in maxillofacial reconstructive surgery are given. The national Collaborative Programme in Additive Manufacturing and the sub-programme on qualification of Ti6Al4V medical implants and aerospace parts produced through additive manufacturing, are discussed. Initial achievements of this programme are shared
Origin of the high piezoelectric response in PbZr(1-x)TixO3
High resolution x-ray powder diffraction measurements on poled PbZr(1-x)TixO3
(PZT) ceramic samples close to the rhombohedral-tetragonal phase boundary (the
so-called morphotropic phase boundary, MPB) have shown that for both
rhombohedral and tetragonal compositions, the piezoelectric elongation of the
unit cell does not occur along the polar directions but along those directions
associated with the monoclinic distortion. This work provides the first direct
evidence for the origin of the very high piezoelectricity in PZT.Comment: 4 pages, 4 EPS figures embedded. More specific title and abstract. To
appear in Phys. Rev. Let
Very Long Baseline Interferometry Measured Proper Motion and Parallax of the -ray Millisecond Pulsar PSR J0218+4232
PSR J02184232 is a millisecond pulsar (MSP) with a flux density 0.9
mJy at 1.4 GHz. It is very bright in the high-energy X-ray and -ray
domains. We conducted an astrometric program using the European VLBI Network
(EVN) at 1.6 GHz to measure its proper motion and parallax. A model-independent
distance would also help constrain its -ray luminosity. We achieved a
detection of signal-to-noise ratio S/N > 37 for the weak pulsar in all five
epochs. Using an extragalactic radio source lying 20 arcmin away from the
pulsar, we estimate the pulsar's proper motion to be
mas yr and mas yr, and a parallax of mas. The very long
baseline interferometry (VLBI) proper motion has significantly improved upon
the estimates from long-term pulsar timing observations. The VLBI parallax
provides the first model-independent distance constraints:
kpc, with a corresponding lower-limit of
kpc. This is the first pulsar trigonometric parallax measurement based
solely on EVN observations. Using the derived distance, we believe that PSR
J02184232 is the most energetic -ray MSP known to date. The
luminosity based on even our 3 lower-limit distance is high enough to
pose challenges to the conventional outer gap and slot gap models.Comment: 5 pages, 2 figures, 2 tables; published in the Astrophysical Journal
Letters on 2014 Feb. 1
Chromosomal Gains and Losses in Uveal Melanomas Detected by Comparative Genomic Hybridization
Eleven uveal melanomas were analyzed using comparative genomic hybridization (CGH). The most abundant genetic changes were loss of chromosome 3, overrepresentation of 6p, loss of 6q, and multiplication of 8q. The smallest overrepresented regions on 6p and 8q were 6pterp21 and 8q24qter, respectively. Several additional gains and losses of chromosome segments were repeatedly observed, the most frequent one being loss of 9p (three cases). Monosomy 3 appeared to be a marker for ciliary body involvement.
CGH data were compared with the results of chromosome banding. Some alterations, e.g., gains of 6p and losses of 6q, were observed with higher frequencies after CGH, while others, e.g., 9p deletions, were detected only by CGH. The data suggest some similarities of cytogenetic alterations between cutaneous and uveal melanoma. In particular, the 9p deletions are of interest due to recent reports about the location of a putative tumor-suppressor gene for cutaneous malignant melanoma in this region
On dual canonical bases
The dual basis of the canonical basis of the modified quantized enveloping
algebra is studied, in particular for type . The construction of a basis for
the coordinate algebra of the quantum matrices is appropriate for
the study the multiplicative property. It is shown that this basis is invariant
under multiplication by certain quantum minors including the quantum
determinant. Then a basis of quantum SL(n) is obtained by setting the quantum
determinant to one. This basis turns out to be equivalent to the dual canonical
basis
Semiclassical Green Function in Mixed Spaces
A explicit formula on semiclassical Green functions in mixed position and
momentum spaces is given, which is based on Maslov's multi-dimensional
semiclassical theory. The general formula includes both coordinate and momentum
representations of Green functions as two special cases of the form.Comment: 8 pages, typeset by Scientific Wor
Photometric stability analysis of the Exoplanet Characterisation Observatory
Photometric stability is a key requirement for time-resolved spectroscopic
observations of transiting extrasolar planets. In the context of the Exoplanet
Characterisation Observatory (EChO) mission design, we here present and
investigate means of translating spacecraft pointing instabilities as well as
temperature fluctuation of its optical chain into an overall error budget of
the exoplanetary spectrum to be retrieved. Given the instrument specifications
as of date, we investigate the magnitudes of these photometric instabilities in
the context of simulated observations of the exoplanet HD189733b secondary
eclipse.Comment: submitted to MNRA
Charmless two-body B decays: A global analysis with QCD factorization
In this paper, we perform a global analysis of and decays
with the QCD factorization approach. It is encouraging to observe that the
predictions of QCD factorization are in good agreement with experiment. The
best fit is around . The penguin-to-tree ratio of decays is preferred to be larger than 0.3.
We also show the confidence levels for some interesting channels: , and , . For decays, they are expected to have smaller branching ratios with
more precise measurements.Comment: 20 pages, 4 figures, version to appear in Phys. Rev.
- âŠ