On improving the iterative convergence properties of an implicit approximate-factorization finite difference algorithm

The iterative convergence properties of an approximate-factorization implicit finite-difference algorithm are analyzed both theoretically and numerically. Modifications to the base algorithm were made to remove the inconsistency in the original implementation of artificial dissipation. In this way, the steady-state solution became independent of the time-step, and much larger time-steps can be used stably. To accelerate the iterative convergence, large time-steps and a cyclic sequence of time-steps were used. For a model transonic flow problem governed by the Euler equations, convergence was achieved with 10 times fewer time-steps using the modified differencing scheme. A particular form of instability due to variable coefficients is also analyzed

Multivariate assessments of activity-related skeletal changes: Interpreting Bell Beaker specialized male archery and social organization in Central Europe

Objectives The Bell Beaker period witnessed the rise of individual inhumations with “wealthy” burial contexts containing archery-related grave goods, leading archaeologists to label the individuals in these tombs as “archers.” This study looks to (1) compare the skeletons from male “archer” burials with those from male “non-archer” burials—those not having archery-related grave goods—in order to assess a possible link between burial context and physical activity, and (2) apply a biomechanics profile to evaluate whether the individuals associated with these “archer” burials practiced specialized archer activity. Materials and Methods The corpus (males only) included 46 “archers” and 40 “non-archers” from Bell Beaker individual inhumations. Osteological data included measurements, scores of entheseal changes, and a diagnosis of certain pathologies. Data analyses involved visual observations, hypothesis tests, dimension reduction, and MANOVA, with approaches aimed at exploring the treatment of data missingness. Results Measurement data revealed no differences between the two groups. Evaluations of entheseal changes found that “non-archers” had consistently more instances of bone surface modifications than “archers.” Individual assessments of specialized archer occupation identified 11 possible specialized archers. Discussion These findings indicate a possible labor differentiation represented through the presence of a probably prestigious “archer” burial context. This suggests a link between grave good presence and labor, but not between a Bell Beaker archery occupation and an “archer” burial context. Data analyses support the application of biomechanics to osteological analyses in order to assess specialized activity on the skeleton

Progressive emergence of double porosity in a silt during compaction

The paper deals with an experimental investigation of water retention properties of a statically compacted unsaturated low plasticity silt. The objective is a deeper understanding of the evolution of an aggregate type fabric at different initial conditions in terms of void ratio and water content. A series of Mercury Intrusion Porosimetry tests (MIP) were performed to provide information about factors influencing fabric changes (effect of mechanical stress due to sample compaction) and fabric-properties relationships (water re-tention curve related to porosimetry). The arrangements of aggregation/particles are also investigated with Environmental Scanning Electron Microscopy (ESEM). The experimental data has been used to calibrate a multimodal water retention model for aggregate which is obtained by linear superposition of sub-curves of the van Genuchten type modified. By comparing the WRC obtained by MIP and under suction controlled conditions it has been found a good agreement between the two method for the drying path

Optimisation and application of ICP-MS and alpha-spectrometry for determination of isotopic ratios of depleted uranium and plutonium in samples collected in Kosovo

The determination of environmental contamination with natural and artificial actinide isotopes and evaluation of their source requires precise isotopic determination of actinides, above all uranium and plutonium. This can be achieved by alpha spectrometry or by inductively coupled plasma mass spectrometry (ICP-MS) after chemical separation of actinides. The performance of a sector-field ICP-MS (ICP-SFMS) coupled to a low-flow micronebulizer with a membrane desolvation unit, "Aridus'', was studied with respect to precise isotopic measurements of uranium and plutonium at the ultratrace level. The UH+/U+ formation rate was about 3x10(-5) and a sensitivity for U-238 of up to 4x10(9) counts s(-1) ppm(-1) was achieved. The limit of quantification (LOQ, 10s) for U-236 and Pu-239 using the experimental arrangement described above was 0.6 pg l(-1) in aqueous solution and 0.13 pg g(-1) in soil, respectively. ICP-SFMS was used in comparison to alpha spectrometry to measure the U and Pu concentrations and isotopic compositions in two soil samples and in one penetrator collected in Kosovo. ICP-MS permitted the determination of U and Pu isotope ratios including the U-236 abundance and Pu-240/Pu-239 ratio at ultratrace levels in soil samples of up to 0.1 g. Depleted uranium (U-235/U-238= 0.00202 +/-0.00001) was determined in one penetrator and one soil sample. Pu concentrations of (5.5 +/-0.1) x 10(-13) g g(-1) and (4.4 +/-0.5) x 10(-13) g g(-1) (Pu-240/Pu-239=0.35 +/-0.10 and 0.27 +/-0.07, respectively) were found in both soil samples from Kosovo. Besides plutonium, U-236 (3.1x10(-5) g g(-1)) and Am-241 (1.7x10(-12) g g(-1)) were also detected in the penetrator sample, which indicates the previous existence of neutron-related processes and points to a possible presence of spent reactor uranium in munitions. However, the most probable plutonium contamination sources in analyzed soil samples from Kosovo are mixed fallout including spent reactor fuel due to the Chernobyl nuclear power plant accident in 1986 and plutonium due to nuclear weapon tests. Additional plutonium contamination could not be determined in the Kosovo soil sample containing depleted uranium with a detection limit of about 10(-13) g g(-1)

Life cycle assessment of synthetic natural gas production from different CO2 sources: A cradle⇂to-gate study

Fuel production from hydrogen and carbon dioxide is considered an attractive solution as long‐term storage of electric energy and as temporary storage of carbon dioxide. A large variety of CO2 sources are suitable for Carbon Capture Utilization (CCU), and the process energy intensity depends on the separation technology and, ultimately, on the CO2 concentration in the flue gas. Since the carbon capture process emits more CO2 than the expected demand for CO2 utilization, the most sustainable CO2 sources must be selected. This work aimed at modeling a Power‐to‐Gas (PtG) plant and assessing the most suitable carbon sources from a Life Cycle Assessment (LCA) perspective. The PtG plant was supplied by electricity from a 2030 scenario for Italian electricity generation. The plant impacts were assessed using data from the ecoinvent database version 3.5, for different CO2 sources (e.g., air, cement, iron, and steel plants). A detailed discussion on how to handle multi‐functionality was also carried out. The results showed that capturing CO2 from hydrogen production plants and integrated pulp and paper mills led to the lowest impacts concerning all investigated indicators. The choice of how to handle multi‐functional activities had a crucial impact on the assessment

Techno-economic evaluation of biomass-to-fuels with solid-oxide electrolyzer

Thermochemical biomass-to-fuel conversion requires an increased hydrogen concentration in the syngas derived from gasification, which is currently achieved by water–gas-shift reaction and CO2 removal. State-of-the-art biomass-to-fuels convert less than half of the biomass carbon with the remaining emitted as CO2. Full conversion of biomass carbon can be achieved by integrating solid-oxide electrolyzer with different concepts: (1) steam electrolysis with the hydrogen produced injected into syngas, and (2) co-electrolysis of CO2 and H2O to convert the CO2 captured from the syngas. This paper investigates techno-economically steam- or co-electrolysis-based biomass-to-fuel processes for producing synthetic natural gas, methanol, dimethyl ether and jet fuel, considering system-level heat integration and optimal placement of steam cycles for heat recovery. The results show that state-of-the-art biomass-to-fuels achieve similar energy efficiencies of 48–51% (based on a lower heating value) for the four different fuels. The integrated concept with steam electrolysis achieves the highest energy efficiency: 68% for synthetic natural gas, 64% for methanol, 63% for dimethyl ether, and 56% for jet fuel. The integrated concept with co-electrolysis can enhance the state-of-the-art energy efficiency to 66% for synthetic natural gas, 61% for methanol, and 54% for jet fuel. The biomass-to-dimethyl ether with co-electrolysis only reaches an efficiency of 49%, due to additional heat demand. The levelized cost of the product of the integrated concepts highly depends on the price and availability of renewable electricity. The concept with co-electrolysis allows for additional operation flexibility without renewable electricity, resulting in high annual production. Thus, with limited annual available hours of renewable electricity, biomass-to-fuel with co-electrolysis is more economically convenient than that with steam electrolysis. For a plant scale of 60 MWth biomass input with the renewable electricity available for 1800 h annually, the levelized cost of product of biomass-to-synthesis-natural-gas with co-electrolysis is 35 $/GJ, 20% lower than that with steam-electrolysis

Stress Echocardiography for Risk Stratification of Diabetic Patients With Known or Suspected Coronary Artery Disease

OBJECTIVE—Coronary artery disease (CAD) is a leading cause of mortality and morbidity in diabetic patients; therefore, their risk stratification is a relevant issue. Because exercise tolerance is frequently impaired in these patients, pharmacological stress echocardiography (SE) has been suggested as a valuable alternative. Our aim was to evaluate the prognostic value of this technique in diabetic patients with known or suspected CAD. RESEARCH DESIGN AND METHODS—A total of 259 consecutive diabetic patients underwent pharmacological SE (dobutamine in 108 patients and dipyridamole in 151 patients) and follow-up for 24 ± 22 months. A comparison between the prognostic value of SE and exercise electrocardiography (ECG) was made in a subgroup of 120 subjects. RESULTS—A total of 13 cardiac deaths and 13 nonfatal infarctions occurred during follow-up, and 58 patients were revascularized. Univariate predictors of outcome were known CAD, positive SE, rest and peak wall motion score index (WMSI), and peak/rest WMSI variation. Peak WMSI was the only significant and independent prognostic indicator (odds ratio 11; 95% CI 4–29, P < 0.0001) on multivariate Cox's analysis. After adjustment for the most predictive clinical and exercise ECG variables, SE provided 43% additional prognostic information (gain in X2 = 7, P < 0.01). Moreover, positive SE was associated with a significantly lower event-free survival. CONCLUSIONS—SE effectively predicts cardiac events in diabetic patients with known or suspected CAD and adds additional prognostic information as compared with exercise ECG