489 research outputs found
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A Knowledge-based Decision Support System for RP&M Process Selection
Due to the large variety of RP&M material/machines and the. strengths/weaknesses
associated with different RP&M processes, the decision·to select a suitableRP&M system
becomes increasingly difficult. This paper presents a knowledge-based approach for the selection
ofsuitable RP&M material/machine to meet specific. requirements ofRP&Mapplications. The
system receives input data on the CAD modelandthe user's specifications,andgenerates outputs
that provide the most appropriate combination ofRP&Mmaterial/machine.·Optimal orientations,
together with estimated manufacturing time and cost, are considered and given in the final
outcome to help the user make the choice.Mechanical Engineerin
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Integrated Decision Support System for Selection of RP Processes
This paper describes an âIntegrated Decision Support System for the Selection of RP
Processes (IDSSSRP)â. The basic methodology proposed in the IDSSSRP is a Sigma approach
towards benchmarking of the Rapid Prototyping (RP) processes. It characterizes a RP process by
using benchmarking and the sigma approach to assess its capability compared to its potential.
Although the six-sigma approach has basically been a management concept and the success of its
implementation has been on process time reduction and quality improvement, this paper adopts
the use of six-sigma tools and benchmarking in the characterization of RP processes. Apart from
geometrical benchmarks, other benchmarks include mechanical benchmarks and process
benchmarks. Benchmarking individual RP processes facilitates standardization and reduces
variability in the prototypes produced by the processes. Following standardizations of
geometrical, mechanical and process benchmarks, a saturated database can then become very
useful in providing decision support to the end user on a particular process as well as a source of
information for benchmarking new RP machines. A case study of the benchmarking process
developed on the Direct Metal Laser Sintering-Selective Laser Sintering (DMLS-SLS) RP
process is presented using the proposed approach. This paper also outlines the working and
implementation of a web-based decision support system based on the IDSSSRP.Mechanical Engineerin
Effective Dynamic Range in Measurements with Flash Analog-to-Digital Convertor
Flash Analog to Digital Convertor (FADC) is frequently used in nuclear and
particle physics experiments, often as the major component in big multi-channel
systems. The large data volume makes the optimization of operating parameters
necessary. This article reports a study of a method to extend the dynamic range
of an 8-bit FADC from the nominal value. By comparing the integrated
pulse area with that of a reference profile, good energy reconstruction and
event identification can be achieved on saturated events from CsI(Tl) crystal
scintillators. The effective dynamic range can be extended by at least 4 more
bits. The algorithm is generic and is expected to be applicable to other
detector systems with FADC readout.Comment: 19 pages, 1 table, 10 figure
Intrinsic Radioactivity in a GSO Crystal and Limits on Double Beta Decay of Gd-160
Scintillating crystal detector offers potential advantages in low-energy
low-background experiments for particle physics and astrophysics. The GSO
crystal is an interesting detector to explore for future neutrino physics
experiments. The contributions to background due to the various channels of
intrinsic radio-isotopes from the Th-232 and U-238 series are identified and
studied with time-correlation analysis and detailed fits to the spectral shape.
Good agreement is achieved between measured and simulated spectra, indicating
background suppression factors to the 10^{-2} - 10^{-3} level are possible. The
procedures can be adopted for background understanding and suppression in other
low-count-rate experiments where the dominant source of background is from
internal radioactivity. Based on 1656 hours of data taking, limits on the
double beta decay half-life for the various channels in Gd-160 are presented.
The limit for the neutrinoless mode is T^{0 \nu \beta \beta}_{{1/2}} > 2.0(0.8)
X 10^{20} y at 68(90)% confidence level.Comment: 25 pages, 3 tables, 6 figure
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Rapid Prototyping of 3D Scaffolds for Tissue Engineering Using a Four-Axis Multiple-Dispenser Robotic System
A desktop rapid prototyping (RP) system has been developed to fabricate scaffolds for tissue
engineering (TE) applications. The system is a computer-controlled four-axis machine with a
multiple-dispenser head. This paper presents the scaffold fabrication process to build free-form
scaffolds from relevant features extracted from given CT-scan images for TE applications. This
involves obtaining the required geometric data for the scaffold in the form of a solid model from
CT-scan images. The extracted scaffold model is then sliced into consecutive two-dimensional
(2D) layers to generate appropriately formatted data for the desktop RP system to fabricate the
scaffolds. The basic material processing involves the sequential dispensing of two or more
materials to form a strand. The four-axis system enables strands to be laid in a different direction
at each layer to form suitable interlacing 3D free-form scaffold structures. The multipledispenser head also allows the introduction of living cells and additional materials during the
scaffold building. The building of the scaffolds with the desktop RP system is described based on
the sequential dispensing of chitosan dissolved in acetic acid and sodium hydroxide solution.
Neutralization of the acetic acid by the sodium hydroxide results in a precipitate to form a gellike chitosan strand.Mechanical Engineerin
Measurement of Trace I-129 Concentrations in CsI Powder and Organic Liquid Scintillator with Accelerator Mass Spectrometry
Levels of trace radiopurity in active detector materials is a subject of
major concern in low-background experiments. Procedures were devised to measure
trace concentrations of I-129 in the inorganic salt CsI as well as in organic
liquid scintillator with Accelerator Mass Spectrometry (AMS) which leads to
improvement in sensitivities by several orders of magnitude over other methods.
No evidence of their existence in these materials were observed. Limits of < 6
X 10^{-13} g/g and < 2.6 X 10^{-17} g/g on the contaminations of I-129 in CsI
and liquid scintillator, respectively, were derived.These are the first results
in a research program whose goals are to develop techniques to measure trace
radioactivity in detector materials by AMS.Comment: Proceedings of 10th International Conference on Accelerator Mass
Spectrometr
Measurement of Ultra-Low Potassium Contaminations with Accelerator Mass Spectrometry
Levels of trace radiopurity in active detector materials is a subject of
major concern in low-background experiments. Among the radio-isotopes, \k40
is one of the most abundant and yet whose signatures are difficult to reject.
Procedures were devised to measure trace potassium concentrations in the
inorganic salt CsI as well as in organic liquid scintillator (LS) with
Accelerator Mass Spectrometry (AMS), giving, respectively, the
\k40-contamination levels of and g/g.
Measurement flexibilities and sensitivities are improved over conventional
methods. The projected limiting sensitivities if no excess of potassium signals
had been observed over background are g/g and g/g for the CsI and LS, respectively. Studies of the LS samples
indicate that the radioactive contaminations come mainly in the dye solutes,
while the base solvents are orders of magnitude cleaner. The work demonstrate
the possibilities of measuring naturally-occurring isotopes with the AMS
techniques.Comment: 18 pages, 4 figures, 3 table
An epidemiological study of epilepsy in Hong Kong SAR, China
SummaryBackgroundSeveral specialist clinic-based epidemiology studies suggested low prevalence in Hong Kong Special Administrative Region (HKSAR) of China. Population-based epidemiological data for epilepsy is not available. We performed the first population-based epidemiological survey of epilepsy in this locality.MethodWe conducted a territory-wide survey. We randomly selected 9547 households from fixed-line telephone directory. We successfully surveyed 17,783 persons of 5178 households by telephone interview. All positive respondents 685 (3.85%) were invited for clinical validation. 127 subjects were validated by board-certified neurologists.ResultsSeizure disorders were confirmed in 28 subjects. The crude prevalence of active epilepsy and seizure disorder were estimated to be 3.94/1000 (95% confidence interval (CI): 2.10â6.74/1000) and 8.49/1000 (95% CI: 5.64â12.27/1000), respectively.ConclusionsThe prevalence of epilepsy in HKSAR is more common than previously thought. The data retrieved is useful for planning and allocation of health resources for patients with seizure disorders
Pulse Shape Discrimination Techniques in Scintillating CsI(Tl) Crystals
There are recent interests with CsI(Tl) scintillating crystals for Dark
Matter experiments. The key merit is the capability to differentiate nuclear
recoil (nr) signatures from the background -events due to
ambient radioactivity on the basis of their different pulse shapes. One of the
major experimental challenges is to perform such pulse shape analysis in the
statistics-limited domain where the light output is close to the detection
threshold. Using data derived from measurements with low energy 's and
nuclear recoils due to neutron elastic scatterings, it was verified that the
pulse shapes between -events are different. Several methods of
pulse shape discrimination are studied, and their relative merits are compared.
Full digitization of the pulse shapes is crucial to achieve good
discrimination. Advanced software techniques with mean time, neural network and
likelihood ratios give rise to satisfactory performance, and are superior to
the conventional Double Charge method commonly applied at higher energies.
Pulse shape discrimination becomes effective starting at a light yield of about
20 photo-electrons. This corresponds to a detection threshold of about 5 keV
electron-equivalence energy, or 4050 keV recoil kinetic energy, in realistic
experiments.Comment: 20 pages, 7 figure
Measurement of the Intrinsic Radiopurity of Cs-137/U-235/U-238/Th-232 in CsI(Tl) Crystal Scintillators
The inorganic crystal scintillator CsI(Tl) has been used for low energy
neutrino and Dark Matter experiments, where the intrinsic radiopurity is an
issue of major importance. Low-background data were taken with a CsI(Tl)
crystal array at the Kuo-Sheng Reactor Neutrino Laboratory. The pulse shape
discrimination capabilities of the crystal, as well as the temporal and spatial
correlations of the events, provide powerful means of measuring the intrinsic
radiopurity of Cs-137 as well as the U-235, U-238 and Th-232 series. The event
selection algorithms are described, with which the decay half-lives of Po-218,
Po-214, Rn-220, Po-216 and Po-212 were derived. The measurements of the
contamination levels, their concentration gradients with the crystal growth
axis, and the uniformity among different crystal samples, are reported. The
radiopurity in the U-238 and Th-232 series are comparable to those of the best
reported in other crystal scintillators. Significant improvements in
measurement sensitivities were achieved, similar to those from dedicated
massive liquid scintillator detector. This analysis also provides in situ
measurements of the detector performance parameters, such as spatial
resolution, quenching factors, and data acquisition dead time.Comment: 28 pages, 12 figure
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