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RISS 인기검색어
- 검색키워드
- 저자 : Spano, J. (검색결과 5 건)
- 무료
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A neural network approach for simulating stationary stochastic processes
Beer, Michael,Spanos, Pol D. Techno-Press 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.32 No.1
In this paper a procedure for Monte Carlo simulation of univariate stationary stochastic processes with the aid of neural networks is presented. Neural networks operate model-free and, thus, circumvent the need of specifying a priori statistical properties of the process, as needed traditionally. This is particularly advantageous when only limited data are available. A neural network can capture the "pattern" of a short observed time series. Afterwards, it can directly generate stochastic process realizations which capture the properties of the underlying data. In the present study a simple feed-forward network with focused time-memory is utilized. The proposed procedure is demonstrated by examples of Monte Carlo simulation, by synthesis of future values of an initially short single process record.
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A neural network approach for simulating stationary stochastic processes
Michael Beer,Pol D. Spanos 국제구조공학회 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.32 No.1
In this paper a procedure for Monte Carlo simulation of univariate stationary stochastic processes with the aid of neural networks is presented. Neural networks operate model-free and, thus, circumvent the need of specifying a priori statistical properties of the process, as needed traditionally. This is particularly advantageous when only limited data are available. A neural network can capture the “pattern” of a short observed time series. Afterwards, it can directly generate stochastic process realizations which capture the properties of the underlying data. In the present study a simple feedforward network with focused time-memory is utilized. The proposed procedure is demonstrated by examples of Monte Carlo simulation, by synthesis of future values of an initially short single process record.
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Influence of scaling procedures on the integrity of titanium nitride coated CAD/CAM abutments
Peter Gehrke,Emmanouil Spanos,Carsten Fischer,Helmut Storck,Florian Tebbel,Dirk Duddeck 대한치과보철학회 2018 The Journal of Advanced Prosthodontics Vol.10 No.3
PURPOSE. To determine the extent of treatment traces, the roughness depth, and the quantity of titanium nitride (TiN) removed from the surface of CAD/CAM abutments after treatment with various instruments. MATERIALS AND METHODS. Twelve TiN coated CAD/CAM abutments were investigated for an in vitro study. In the test group (9), each abutment surface was subjected twice (150 g vs. 200 g pressure) to standardized treatment in a simulated prophylaxis measure with the following instruments: acrylic scaler, titanium curette, and ultrasonic scaler with steel tip. Three abutments were used as control group. Average surface roughness (Sa) and developed interfacial area ratio (Sdr) of treated and untreated surfaces were measured with a profilometer. The extent of treatment traces were analyzed by scanning electron microscopy. RESULTS. Manipulation with ultrasonic scalers resulted in a significant increase of average surface roughness (Sa, P<.05) and developed interfacial area ratio (Sdr, P<.018). Variable contact pressure did not yield any statistically significant difference on Sa-values for all instruments (P=.8). Ultrasonic treatment resulted in pronounced surface traces and partially detachment of the TiN coating. While titanium curettes caused predominantly moderate treatment traces, no traces or detectable substance removal has been determined after manipulation with acrylic curettes. CONCLUSION. Inappropriate instruments during regular plaque control may have an adverse effect on the integrity of the TiN coating of CAD/CAM abutments. To prevent defects and an increased surface roughness at the transmucosal zone of TiN abutments, only acrylic scaling instruments can be recommended for regular maintenance care.
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Hydrophilic silica additives for disulfonated poly(arylene ether sulfone) random copolymer membranes
Lee, C.H.,Xie, W.,VanHouten, D.,McGrath, J.E.,Freeman, B.D.,Spano, J.,Wi, S.,Park, C.H.,Lee, Y.M. Elsevier Scientific Pub. Co 2012 Journal of membrane science Vol.392 No.-
Hydrophilic silica (SiO<SUB>2</SUB>) nanoparticles (average size=7nm), which act as inorganic acids at low pH (<2), were added together with a PEO-PPO-PEO triblock copolymer dispersant to a random disulfonated poly(arylene ether sulfone) copolymer in the potassium salt (?SO<SUB>3</SUB><SUP>-</SUP>K<SUP>+</SUP>) form in order to control permeation and rejection characteristics of the homopolymer. The dispersants (shell) absorbed on the surface of SiO<SUB>2</SUB> nanoparticles (core) formed a distinctive core-shell structure. The PEO units located at the outside of the dispersant formed complexes with ?SO<SUB>3</SUB><SUP>-</SUP>K<SUP>+</SUP> groups of BPS-20 via ion-dipole interactions. These interactions induced a compatible binary system following the Flory-Fox equation associated with glass transition temperature (T<SUB>g</SUB>) depression and prevented extraction of the water-soluble dispersant even under aqueous conditions. The ion-dipole interaction, combined with hydrogen bonding between SiO<SUB>2</SUB> and the dispersant, caused SiO<SUB>2</SUB> nanoparticles to be well distributed within the BPS-20 matrix up to a limit of 1wt.% of SiO<SUB>2</SUB> and minimized the formation of non-selective cavities within the matrix's hydrophilic water channels. The resulting BPS-20_SiO<SUB>2</SUB> nanocomposites showed improved salt rejection and reduced ionic conductivity. These trends are analogous to those of disulfonated copolymer systems, with polar groups creating hydrogen bonding or acid-base complexation with ?SO<SUB>3</SUB><SUP>-</SUP>K<SUP>+</SUP> groups in BPS copolymers. Well dispersed SiO<SUB>2</SUB> nanoparticles in highly water-permeable desalination membranes are expected to result in an increase in salt rejection but very little change in water permeability. The addition of nanoparticles to desalination membranes may offset the permeability-selectivity tradeoff observed in polymer membranes. Above 1wt.%, SiO<SUB>2</SUB> nanoparticles increased both the interchain distance between polymer chains and the water uptake. However, the increased hydrophilicity due to high SiO<SUB>2</SUB> content did not yield improved water permeation of the nanocomposite membranes. The SiO<SUB>2</SUB> nanoparticles acted as barriers, hindering water passage (restrictive diffusion) and lowering water permeability. Meanwhile, acidic hydroxyl groups (OH<SUB>2</SUB><SUP>+</SUP>) on the SiO<SUB>2</SUB> surface in the sulfonate matrix led to improved ionic conductivity, but NaCl rejection capability decreased because the concentration of ?SO<SUB>3</SUB><SUP>-</SUP>K<SUP>+</SUP> was diluted by highly absorbed water molecules, resulting in weakened Donnan exclusion. The mechanical properties and chlorine resistance of all BPS-20_SiO<SUB>2</SUB> nanocomposites were comparable to those of BPS-20.
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