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Spiral Growth Manufacturing (SGM) – A Continuous Additive Manufacturing Technology for Processing Metal Powder by Selective Laser Melting
Spiral growth manufacturing is a new innovative powder based rapid manufacturing
technique. The innovation exists in the methodology in which powder layers are deposited.
Unlike other pre-placed powder systems, the deposited layers move relative to the location at
which they are processed. This is made possible by a rotating build drum into which powder is
deposited, in spiralled layers, from a stationary hopper. With this configuration powder can be
continuously deposited and levelled and simultaneously processed, eliminating delays in the
build cycle. Stainless steel and cobalt-chrome powder is selectively melted using a 100W flash
lamp pumped Nd:YAG laser. This paper reports on factors affecting build rate and on build
strategies for creating a number of axis-symmetric thin and thick walled cylinders. Experimental
results suggest that build rate for thin walled structures bonded to a substrate will ultimately be
governed by tangential movements of the powder particles when frictional forces are not
sufficient to accelerate the particles along a curved path, provided that enough laser power is
available for melting. Even melt pool balling, which is evident when melting one layer at high
speeds, diminishes in multiple layer builds due to re-melting and infilling.Mechanical Engineerin
Using a task-based approach in evaluating the usability of BoBIs in an e-book environment
This paper reports on a usability evaluation of BoBIs (Back-of-the-book Indexes) as searching and browsing tools in an e-book environment. This study employed a task-based approach and within-subject design. The retrieval performance of a BoBI was compared with a ToC and Full-Text Search tool in terms of their respective effectiveness and efficiency for finding information in e-books. The results demonstrated that a BoBI was significantly more efficient (faster) and useful compared to a ToC or Full-Text Search tool for finding information in an e-book environment
The Cosmic Coincidence as a Temporal Selection Effect Produced by the Age Distribution of Terrestrial Planets in the Universe
The energy densities of matter and the vacuum are currently observed to be of
the same order of magnitude: . The cosmological window of time during which this occurs is
relatively narrow. Thus, we are presented with the cosmological coincidence
problem: Why, just now, do these energy densities happen to be of the same
order? Here we show that this apparent coincidence can be explained as a
temporal selection effect produced by the age distribution of terrestrial
planets in the Universe. We find a large () probability that
observations made from terrestrial planets will result in finding at
least as close to as we observe today. Hence, we, and any
observers in the Universe who have evolved on terrestrial planets, should not
be surprised to find . This result is
relatively robust if the time it takes an observer to evolve on a terrestrial
planet is less than Gyr.Comment: Submitted to Ap
The Arecibo Methanol Maser Galactic Plane Survey - II: Statistical and Multi-wavelength Counterpart Analysis
We present an analysis of the properties of the 6.7 GHz methanol maser sample
detected in the Arecibo Methanol Maser Galactic Plane Survey. The distribution
of the masers in the Galaxy, and statistics of their multi-wavelength
counterparts is consistent with the hypothesis of 6.7 GHz maser emission being
associated with massive young stellar objects. Using the detection statistics
of our survey, we estimate the minimum number of methanol masers in the Galaxy
to be 1275. The l-v diagram of the sample shows the tangent point of the
Carina-Sagittarius spiral arm to be around 49.6 degrees, and suggests
occurrence of massive star formation along the extension of the Crux-Scutum
arm. A Gaussian component analysis of the maser spectra shows the mean
line-width to be 0.38 km/s which is more than a factor of two larger than what
has been reported in the literature. We also find no evidence that faint
methanol masers have different properties than those of their bright
counterparts.Comment: Accepted by ApJ; Revised footnote number 3 on page 8 based on private
communicatio
The management of type 1 and type 2 diabetes in pregnancy
Pregestational diabetes is a common medical complication of pregnancy and preconception planning is an essential component of care for affected women of childbearing age. Once pregnant, structured care in a multidisciplinary team setting is necessary to ensure optimal outcomes. Although significant progress has been made, these women and their offspring remain to have a significantly elevated risk of multiple adverse complications. Structured programmes using information technology and enabling access to novel technologies may facilitate our goal of ensuring an outcome closer to that of a pregnancy unaffected by diabetes
Stochastic series expansion method for quantum Ising models with arbitrary interactions
A quantum Monte Carlo algorithm for the transverse Ising model with arbitrary
short- or long-range interactions is presented. The algorithm is based on
sampling the diagonal matrix elements of the power series expansion of the
density matrix (stochastic series expansion), and avoids the interaction
summations necessary in conventional methods. In the case of long-range
interactions, the scaling of the computation time with the system size N is
therefore reduced from N^2 to Nln(N). The method is tested on a one-dimensional
ferromagnet in a transverse field, with interactions decaying as 1/r^2.Comment: 9 pages, 5 figure
Low-Frequency Radio Transients in the Galactic Center
We report the detection of a new radio transient source, GCRT J1746-2757,
located only 1.1 degrees north of the Galactic center. Consistent with other
radio transients toward the Galactic center, this source brightened and faded
on a time scale of a few months. No X-ray counterpart was detected. We also
report new 0.33 GHz measurements of the radio counterpart to the X-ray
transient source, XTE J1748-288, previously detected and monitored at higher
radio frequencies. We show that the spectrum of XTE J1748-288 steepened
considerably during a period of a few months after its peak. We also discuss
the need for a more efficient means of finding additional radio transients
Confirmation of the Luminous Blue Variable nature of AFGL 2298
We present new photometric and spectroscopic observations of the stellar source AFGL 2298 (= IRAS 18576+0341) that has recently been proposed as a candidate Luminous Blue Variable (LBV). Our data confirm that the star is a highly luminous B supergiant which is both spectroscopically and photometrically variable. Assuming a distance of 10 kpc, comparison of the 2001 June data to synthetic spectra suggest stellar parameters of T=12.5 kK, log(L/L⊙)=6.2 and Ṁ=5xE-5 M⊙ yr-1. Data obtained in 2002 August indicate an increase in both temperature (=15 kK) and mass loss rate (=1.2xE-4 M⊙ yr-1) at constant bolometric luminosity. These physical parameters place AFGL 2298 at the Humphreys-Davidson limit for the most luminous stars known. We conclude that the position of AFG 2298 in the HR diagram, the significant variability observed between 1999-2002 and presence of a massive ejection nebula are consistent with a classification of AFGL 2298 as a bona fide LBV
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