Optimal sampling schedule for parameter estimation of linear models with unknown but bounded measurement errors

The problem of optimal sampling design for parameter estimation when data are generated by linear models is addressed. The measurements are assumed to be corrupted by an unknown but bounded additive noise. The sampling design assumes that the number of samples is unconstrained and no replication is allowed. Two main results are shown: 1) for particular classes of linear models, the optimal number of measurements is equal to the number of parameters, as in the statistical context; 2) the uncertainty intervals of the parameter estimates are bounded from above by quantities that can be computer a priori, knowing only the model and the error structure.     

Effect of water inclusions on charge transport and polarization inporous media

Wideband dielectric spectroscopy measurements (100 Hz to 10 GHz) were carried out on different microporous systems (including sintered glass filters, sandstone and carbonate rocks) saturated with brine (electrolytic water solution) and a hydrocarbon oil at different relative fractions. Three main contributions were singled out in the dielectric spectra: low frequency dispersion (LFD) effects (<100 kHz) related to long range ionic transport and dependent on the connectivity of the water phase; Maxwell-Wagner-Sillars (MWS) polarization effects (100 kHz to 1 GHz), essentially controlled by the shape of the water inclusions; and high-frequency effects (>1 GHz) due to short-range ion transport and related to specific pore surface. For each analyzed system, oil-wet (o-W) and water-wet (w-w) samples were obtained by chemical treatment of the pore surfaces. Systematic differences were observed in the electrical response on varying wettability (and so the respective distribution of the fluids in the pore space). Parameters such as the loss tangent value, the strength and the exponent of the LFD power law, as well as the characteristic time and strength of the MWS relaxation were good indicators of wettability. Results were discussed by using some standard models that account for the pore wettability effects on dielectric spectra. A new method for wettability determination of reservoir rocks from both laboratory and borehole electric measurements was presented     

Microscopical features in retrieved human Branemark implants: a report of 19 cases

The authors present a histologic analysis of 19 Branemark titanium implants retrieved for different causes: four implants were removed for abutment fracture, one for dental nerve dysesthesia, two for bone overheating, two for peri-implantitis, nine for mobility, one for unknown causes. In the implants removed for fracture a high bone-implant contact percentage was present (71.83 +/- 4.96%) with compact, mature bone at the interface. The picture of the failure due to bone overheating was characteristic with the presence of bone sequestra and of a gap between implant and bone filled by lymphocytes and plasma cells: many bacteria surrounded the necrotic bone and no newly regenerated bone was present. In peri-implantitis an inflammatory infiltrate was observed in the peri-implant tissues: a dense fibrous connective tissue was present around implants failed for mobility. The microscopical picture is certainly extremely important in identifying the causal determinants of an implant failure.     

原料油汽化特性对催化裂化反应结焦过程影响的CFD模拟

为考察原料油汽化特性影响,在一套百万吨级工业FCC提升管中,基于多相欧拉模型耦合EMMS曳力和传质、油滴汽化和十二集总反应动力学模型,采用三维CFD模拟研究气液固三相流动、汽化、反应、结焦的复杂过程,新开发结焦预测模型定量预测结焦状况,对比研究不同原料油雾化液滴粒径和起始汽化温度下各相和反应组分浓度场、温度场分布和结焦程度。结果表明,模拟方法可较准确预测汽化、反应生焦和结焦过程,不同雾化液滴粒径和起始汽化温度通过流场分布和汽化快慢影响液相油滴汽化率和反应转化率;合适液滴粒径(60 μm)和起始汽化温度(654 K)可提升轻油、汽油、液化石油气目标产品收率并改善结焦程度。     

A very short planar silica spot-size converter using a nonperiodicsegmented waveguide

To reduce the coupling loss of a fiber-to-ridge waveguide connection, a planar silica spot-size converter for a wavelength of 1.55 μm is implemented in the form of a nonperiodic segmented waveguide structure with irregular tapering. A simple single-step lithography process is sufficient for the fabrication of the planar structures. An evolutionary algorithm has been successfully applied for the optimization. The simulated results obtained with a three-dimensional (3-D) finite difference beam propagation method (FD-BPM) program are compared with measurements of implemented couplers, showing very good agreement. A waveguide-to-fiber coupling efficiency improvement exceeding 2 dB per converter is shown. Structures obtained with this approach are very short (~140 μm) and simple to integrate on the same wafer with other planar structures such as phased arrays or ring resonator structures     

Comparison of simulation and measurement of dynamic fiber-coupling effects for high-speed multimode VCSELs

Static and dynamic measurements are performed with GaAs oxide-confined vertical-cavity surface-emitting lasers (VCSELs), using multimode fibers with a core diameter of 50 and 62.5 /spl mu/m and different numerical apertures (NAs). They show that a small NA can have a severe impact on the eye opening and thus also on the bit-error rate. The measurements are analyzed with a spatiotemporal two-dimensional (2-D) multimode VCSEL model. The required parameter extraction for the model is verified with small- and large-signal measurements. The analysis shows that the change of the eye opening can be explained by the interaction between the mode- and the current-injection profile, carrier diffusion, and intermodal gain compression (IGC). IGC increases differences in the modal power distribution caused by the interaction between the mode profiles and the current-injection profile. Carrier diffusion is able to compensate these increased differences of the modal power distribution. Its impact, however, on dynamic changes caused by IGC is moderate.     

Experimental characterisation of a CuAg alloy for thermo‐mechanical applications. Part 2: Design strain‐life curves estimated via statistical analysis

Strain‐life fatigue data on copper alloys, especially type CuAg, are seldom available in the literature. This work fills this gap by estimating the strain‐life curves of a CuAg alloy used for thermo‐mechanical applications, from isothermal low‐cycle fatigue tests at 3 temperatures (room temperature, 250°C, 300°C). Regression analysis is used to estimate the median fatigue curves at 50% survival probability. The comparison of median curves with the Universal Slopes Equation model, calibrated on monotonic tensile properties, shows a fairly good agreement. Design strain‐life curves with a lower failure probability and given confidence are estimated by several approximate statistical methods (“Equivalent Prediction Interval,” univariate tolerance interval, Owen's tolerance interval for regression). When higher survival probabilities are considered, the results show a marked decrease in the allowable design strain at a prescribed fatigue life. The suggested procedure thus improves the durability analysis of components loaded thermo‐mechanically.