4,518 research outputs found
Recommended from our members
Effect of Processing Parameters on the Density and Microstructure of Direct Laser Sintered Al-12Si Powders
The effect of processing parameters on the sintering behaviour of gas atomised Al-12Si
powders has been investigated. Laser power, scanning rate, scan spacing and layer
thickness are found to control the densification and the resultant microstructural
characteristics of the laser sintered parts. It was found that sintered density increased as
the energy density increased reaching a maximum of 80.2% at an energy input per unit
volume of 67 J mm-3. For parts produced with a slightly lower power density (50 J mm-3), the microstructure consisted of fine dendrites with interconnected porosity while parts
fabricated with a slightly higher power density (100 J mm-3) were noted to have a
preponderance of coarse dendrites with a discontinuous network of irregular shaped pores
surrounded by a fully dense aluminium-silicon matrix.Mechanical Engineerin
Recommended from our members
Selective Laser Sintering of Polymer Nanocomposites
This paper describes the fabrication and characterization of polymer nanocomposite (PNC)
materials for use in the selective laser sintering (SLS) process. PNC materials are of great
interest generally because of their excellent physical properties, and offer excellent potential
in rapid manufacturing of structural polymeric parts. Three different nano additive materials
have been used: cerium oxide IV, yttrium stabilized zirconia, and layered Hectorite clay.
These materials have been used to reinforce PA6 polymer using solution blending and spray
drying to create powder with particle sizes in the range of 5-40 µm. The mechanical
properties and microstructure of the PNC materials have been evaluated and the results
compared to those of unfilled polymer.Mechanical Engineerin
History of Francestown, N. H., from its earliest settlement April, 1758, to January 1, 1891 : with a brief genealogical record of all the Francestown families.
2 folded maps.; Genealogies: p. [475]-1007
Shunt insertion in the summer: is it safe?
Journal ArticleObject. The potential for increased complications related to the arrival of new residents in July each year has not previously been demonstrated in the neurosurgical literature. The authors investigated this phenomenon in children undergoing cerebrospinal fluid shunt surgery. Methods. Data were obtained from a multicenter hydrocephalus clinical trials database and from hospital admission records in English-speaking Canada. Data pertaining to patients treated in July and August were compared with those pertaining to patients treated during the remainder of the year. The incidence of shunt failure, shunt infection, neurological deficits, wound infection, technical errors, and death were compared using a chi-square test for categorical outcomes, means for continuous outcomes, and survival analysis for time-dependent outcomes. In the hydrocephalus clinical trials database, 138 of 737 patients were treated in July and August. The median duration of shunt lifespan (hereafter referred to as "shunt survival") was 1.7 years for patients treated during the summer months and 2.4 years for those treated throughout the rest of the year (p = 0.10); for shunt infection the figures were 13.8 and 8.8% (p = 0.08) of the total number of cases, and for wound dehiscence they were 2.9 and 0.7% (p = 0.05), respectively. When all shunt procedures were included, an examination of shunt survival and infection incidence rates recorded in the Canadian Hospital Discharge Database seemed to imply a significant advantage to having surgery between September and June (log-rank statistic = 7.10, p = 0.008). Conclusions. The data suggest a "July effect" on some outcomes related to shunt surgery, but the effect was small. Nonetheless, the potential morbidity of shunt failure, infection, and the cost of treatment indicate that continued vigilance and appropriate supervision of new staff by attending surgeons is warranted
Portfolio efficiency and discount factor bounds with conditional information:An Empirical Study
Using ultra-thin parylene films as an organic gate insulator in nanowire field-effect transistors
We report the development of nanowire field-effect transistors featuring an
ultra-thin parylene film as a polymer gate insulator. The room temperature,
gas-phase deposition of parylene is an attractive alternative to oxide
insulators prepared at high temperatures using atomic layer deposition. We
discuss our custom-built parylene deposition system, which is designed for
reliable and controlled deposition of <100 nm thick parylene films on III-V
nanowires standing vertically on a growth substrate or horizontally on a device
substrate. The former case gives conformally-coated nanowires, which we used to
produce functional -gate and gate-all-around structures. These give
sub-threshold swings as low as 140 mV/dec and on/off ratios exceeding at
room temperature. For the gate-all-around structure, we developed a novel
fabrication strategy that overcomes some of the limitations with previous
lateral wrap-gate nanowire transistors. Finally, we show that parylene can be
deposited over chemically-treated nanowire surfaces; a feature generally not
possible with oxides produced by atomic layer deposition due to the surface
`self-cleaning' effect. Our results highlight the potential for parylene as an
alternative ultra-thin insulator in nanoscale electronic devices more broadly,
with potential applications extending into nanobioelectronics due to parylene's
well-established biocompatible properties
The effect of temperature and gas flow on the physical vapour growth of mm-scale rubrene crystals for organic FETs
There has recently been significant interest in rubrene single-crystals grown
using physical vapour transport techniques due to their application in
high-mobility organic field-effect transistor (OFET) devices. Despite numerous
studies of the electrical properties of such crystals, there has only been one
study to date focussing on characterising and optimising the crystal growth as
a function of the relevant growth parameters. Here we present a study of the
dependence of the yield of useful crystals (defined as crystals with at least
one dimension of order 1 mm) on the temperature and volume flow of carrier gas
used in the physical vapour growth process.Comment: Submitted for Proceedings of SPIE Microelectronics, MEMS and
Nanotechnology Conference, Canberra, Australia, 4-7 Dec. 07. 8 Page
Young people and political action: who is taking responsibility for positive social change?
A human rights perspective suggests that we are all responsible for ensuring the human rights of others, which in turn ensures that our own human rights are respected and protected. A convenience sample of 108 young people (41 males and 67 females) aged between 16 and 25 completed a questionnaire which asked about (a) levels of involvement in political activity and (b) sense of personal responsibility for ensuring that the human rights of marginalised groups (e.g. ethnic minorities, immigrants, lesbians and gay men) are protected. Findings showed that most respondents supported (in principle) the notion of human rights for all, but tended to engage in low key political activity (e.g. signing petitions; donating money or goods to charity) rather than actively working towards positive social change. Qualitative data collected in the questionnaire suggested three main barriers to respondents viewing themselves as agents of positive social change: (1) "It’s not my problem", (2) "It’s not my responsibility", and (3) a sense of helplessness. Suggestions for how political action might best be mobilised among young people are also discussed.</p
Macroscopically distinct quantum superposition states as a bosonic code for amplitude damping
We show how macroscopically distinct quantum superposition states
(Schroedinger cat states) may be used as logical qubit encodings for the
correction of spontaneous emission errors. Spontaneous emission causes a bit
flip error which is easily corrected by a standard error correction circuit.
The method works arbitrarily well as the distance between the amplitudes of the
superposed coherent states increases.Comment: 4 pages, 2 postscript figures, LaTeX2e, RevTeX, minor changes, 1
reference adde
Pricing Options in Incomplete Equity Markets via the Instantaneous Sharpe Ratio
We use a continuous version of the standard deviation premium principle for
pricing in incomplete equity markets by assuming that the investor issuing an
unhedgeable derivative security requires compensation for this risk in the form
of a pre-specified instantaneous Sharpe ratio. First, we apply our method to
price options on non-traded assets for which there is a traded asset that is
correlated to the non-traded asset. Our main contribution to this particular
problem is to show that our seller/buyer prices are the upper/lower good deal
bounds of Cochrane and Sa\'{a}-Requejo (2000) and of Bj\"{o}rk and Slinko
(2006) and to determine the analytical properties of these prices. Second, we
apply our method to price options in the presence of stochastic volatility. Our
main contribution to this problem is to show that the instantaneous Sharpe
ratio, an integral ingredient in our methodology, is the negative of the market
price of volatility risk, as defined in Fouque, Papanicolaou, and Sircar
(2000).Comment: Keywords: Pricing derivative securities, incomplete markets, Sharpe
ratio, correlated assets, stochastic volatility, non-linear partial
differential equations, good deal bound
- …