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

Integrated Decision Support System for Selection of RP Processes

This paper describes an ‘Integrated Decision Support System for the Selection of RP Processes (IDSSSRP)’. 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 $\rm{2^8}$ 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

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 $\sim 10^{-10}$ and $\sim 10^{-13}$ 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 $8 \times 10^{-13}$ g/g and $3 \times 10^{-17}$ 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): 2.10–6.74/1000) and 8.49/1000 (95% CI: 5.64–12.27/1000), 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 $\beta / \gamma$-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 $\gamma$'s and nuclear recoils due to neutron elastic scatterings, it was verified that the pulse shapes between $\beta / \gamma$-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 40$-$50 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