Mixed eight-node (hexahedron) solid-shell elements based on the standard or partial version of the three-field Hu–Washizu (HW) functionals are developed for Green strain. Three
reduced ...representations
of the assumed stress/strain fields are selected. They improve effectiveness, yet retaining good accuracy and convergence properties. At the outset, the standard HW functional and the assumed stress/strain representations of the 3D solid element B8-15P (Weissman in Int J Numer Methods Eng 39:2337–2361, 1996) are used to derive a solid-shell element with 51 parameters. To eliminate locking, the ANS method is applied to the thickness strain (Betsch and Stein in Commun Numer Methods Eng 11:899–909, 1995) and to the transverse shear strain (Dvorkin and Bathe in Eng Comput 1:77–88, 1984). It is a correct element which, however, yields too large displacements for coarse meshes and trapezoidal through-thickness shapes. To improve the above formulation, the
ζ
-independent
reduced representations
of the assumed stress/ strain fields are selected and the transformations to Cartesian components are modified. The thickness strain is enhanced by the EAS method. The element with 35 parameters is derived from the standard/enhanced HW functional, but, to further reduce the assumed fields, partial/enhanced HW functionals are constructed from the 3D potential energy by applying the Lagrange multiplier method only to selected strain components. In the element with 27 parameters, this is applied to the constant in-plane strain and to the transverse shear strain while in the element with 19 parameters, to the constant in-plane strain only.Two other modifications are implemented to enhance the behavior of these elements: (A) the skew coordinates are used in the
reduced representations
of the in-plane stress/strain (Wisniewski and Turska in Int J Numer Methods Eng 90:506–536, 2012), and (B) the
Residual Bending Flexibility
correction of the transverse shear stiffness (MacNeal in Comput Struct 8(2):175–183, 1978) is adapted. Finally, the performance of the proposed solid-shell HW elements is demonstrated on several linear and non-linear examples for the linear elastic material and the hyper-elastic material. The proposed elements are compared to each other and to the best existing elements of this class.
In this study, the IWA Activated Sludge Model No. 2d (ASM2d) was expanded to identify the most important mechanisms leading to the anoxic nitrous oxide (N2O) production in the combined nitrogen (N) ...and phosphorus (P) removal activated sludge systems. The new model adopted a three-stage denitrification concept and was evaluated against the measured data from one/two-phase batch experiments carried out with activated sludge withdrawn from a local, large-scale biological nutrient removal wastewater treatment plant. The experiments were focused on investigating the effects of different external carbon sources (acetate, ethanol) and electron acceptors (nitrite, nitrate) on the mechanisms of N2O production in enhanced biological P removal by polyphosphate accumulating organisms (PAOs) and external carbon-based denitrification by ordinary heterotrophic organisms (OHOs). The experimental results explicitly showed that N2O production was predominantly governed by the presence of nitrite in the reactor regardless of the examined carbon source and the ratio COD/N in the reactor. The model was capable of accurately predicting (with R2 > 0.9) the behavior of not only N2O-N, but also NO3-N, NO2-N, soluble COD, and PO4-P. The simulation results revealed that only OHOs were responsible for N2O production, whereas the present denitrifying PAOs reduced only nitrate to nitrite.
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•N2O production by the full-scale EBPR sludge was discussed.•Minor N2O production was observed in the experiments with nitrate and different carbon sources.•When nitrite was present, significant N2O accumulation and lack of PO4-P uptake occurred.•ASM2d was expanded to identify the most important mechanisms leading to the N2O production.•During calibration and validation, model predictions matched accurately all the experimental data (R2 > 0.8).
The 9-node quadrilateral shell element MITC9i is developed for the Reissner-Mindlin shell kinematics, the extended potential energy and Green strain. The following features of its formulation ensure ...an improved behavior: 1. The MITC technique is used to avoid locking, and we propose improved transformations for bending and transverse shear strains, which render that all patch tests are passed for the regular mesh, i.e. with straight element sides and middle positions of midside nodes and a central node. 2. To reduce shape distortion effects, the so-called corrected shape functions of Celia and Gray (Int J Numer Meth Eng 20:1447–1459,
1984
) are extended to shells and used instead of the standard ones. In effect, all patch tests are passed additionally for shifts of the midside nodes along straight element sides and for arbitrary shifts of the central node. 3. Several extensions of the corrected shape functions are proposed to enable computations of non-flat shells. In particular, a criterion is put forward to determine the shift parameters associated with the central node for non-flat elements. Additionally, the method is presented to construct a parabolic side for a shifted midside node, which improves accuracy for symmetric curved edges. Drilling rotations are included by using the drilling Rotation Constraint equation, in a way consistent with the additive/multiplicative rotation update scheme for large rotations. We show that the corrected shape functions reduce the sensitivity of the solution to the regularization parameter
γ
of the penalty method for this constraint. The MITC9i shell element is subjected to a range of linear and non-linear tests to show passing the patch tests, the absence of locking, very good accuracy and insensitivity to node shifts. It favorably compares to several other tested 9-node elements.
Biological invasions cause biodiversity erosion on a global scale. Invasive species spreading beyond their natural range compete with native fauna for food and space, push native species to ...suboptimal habitats, impairing their behaviour and thus limiting their occurrence. Freshwater ecosystems are especially vulnerable to biological invasions and their ecological and economic impacts. The invasive Asian clams (Corbicula spp.), due to their opportunistic life style, can occur at densities of thousands ind. m−2. They act as ecosystem engineers transforming bottom substrata through accumulation of shells. Our goal was to determine the effect of substratum modification by living Corbicula and their shells on substratum choice and behaviour of Unio tumidus and Anodonta anatina, two European freshwater mussel species of the highly imperilled Unionidae family. We assessed their substratum selection in pairwise choice tests (pure sand vs. sand modified by living Corbicula or their shells, sand modified by shells vs. living Corbicula). Next, we tested locomotion and burrowing of unionids on pure substratum and substrata modified by Corbicula. Unionids avoided sand modified by living Corbicula and their empty shells, not distinguishing between these two types of substratum modification. In the presence of Corbicula, their burrowing was shallower or it took them longer to obtain the same depth as in the pure sand. Additionally, on sand modified by Corbicula shells, we observed a locomotion increase (U. tumidus) or slowing down (A. anatina). Our research showed a novel mechanism of negative impact of Corbicula on unionids, consisting in pushing them away from their optimal habitats. This may contribute to their habitat loss and future declines in invaded ecosystems.
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•Impact of Corbicula on European unionids: U. tumidus (Ut) and A. anatina (Aa)•Sand modification by Corbicula negatively affected unionids•Unionids avoided sand modified by Corbicula and their shells•Unionids burrowed less in sand with living Corbicula and their shells•Locomotion of Ut increased and that of Aa slowed down in sand with Corbicula
Infaunal freshwater mussels are highly threatened and declining worldwide. One of the potential threats to mussels consists of biological invasions. We intended to investigate the habitat overlap and ...behavioural differences between native (Unio pictorum, Unio tumidus, Anodonta anatina, Anodonta cygnea) and invasive (Asian Sinanodonta woodiana) unionid bivalves to determine potential sources of competition. Furthermore, we investigated differences between S. woodiana from the established population in artificially heated waters and from the recent population in a natural thermal regime. We used pairwise choice tests on mud, medium, coarse and very coarse sand, mixture of medium and coarse sand, fine, medium and coarse gravel, and observed mussel locomotion and burrowing in preferred and non-preferred substrata. All species generally preferred fine-grained materials. The widest preference range was exhibited by S. woodiana (both populations), whereas A. cygnea was the most selective. The preferences of the cold-water population of S. woodiana were shifted towards coarser materials compared to conspecifics from the heated waters, and highly overlapped with the preferences of the native species. Anodonta cygnea most often moved horizontally and spent the shortest time deeply burrowed. Both Unio species were deeply burrowed for the largest amount of time and the horizontal locomotion of U. tumidus was the lowest among the test species. Sinanodonta woodiana, especially from the heated water population, exhibited relatively weak locomotion (compared to A. cygnea) and burrowing (compared to Unio spp. and A. anatina). Deep burrowing was more common on fine-grained materials. Our results suggest that the native mussels can be threatened by S. woodiana due to their overlapping habitat preferences, potentially hindering habitat separation. However, mobile native mussels may be capable of migrating and avoiding competition. Accumulating knowledge of the biology and ecology of freshwater mussels could contribute to the creation and improvement of conservation plans to protect these threatened animals.
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•Habitat overlap, locomotion and burrowing of invasive and native European Unionidae•Invasive S. woodiana has wider substratum preferences overlapping with natives.•S. woodiana is less mobile and burrows less often compared to native species.•Native mussels are likely to co-occur and face competition of spreading S. woodiana.•S. woodiana from cold and heated waters differs in habitat preferences and burrowing.
Deep level transient spectroscopy (DLTS) measurements on multilayer devices can be influenced by secondary barriers. Our starting point is a simple model used in the literature for simulations of ...DLTS signals induced by such barriers: the structure is represented by two diodes connected back-to-back and separated by a neutral region. Although the calculations confirm that capacitance transients can occur in multilayer structures without defects, we find that the quantitative modeling of corresponding DLTS peaks resembling the N1 signal in Cu(In,Ga)Se2 solar cells requires unphysical input parameters. Therefore, we carefully analyze the assumptions of the model and investigate the limits of its applicability. We look into details of the formation of a DLTS signal and unveil the connection between observed kinetics, capacitance-voltage profiles, and the shape of DLTS peaks. We show that the signals originating from secondary barriers exhibit a logarithmic dependence on the pulse duration which can mimic a response from extended defects. We also verify the validity of the criterion existing in the literature allowing to distinguish signals coming from a back contact and deep defects and show that it can be used only in very specific situations.
In this paper platinum (Pt) doped tungsten trioxide (WO3) layers have been investigated. The structures were prepared in the standard thick film technology. A scanning electron microscope (SEM) was ...used for the microstructure analysis of the gas sensitive layers. The work function was examined by using a scanning Kelvin probe (SKP). The Kelvin probe is a non-contact and non-destructive method to provide work function measurements and surface analysis. This tool is very sensitive to any surface potential changes of the investigated material. The measurements preformed by using the SKP shows that the screen printed WO3 layers were very homogenous and no significant defects are present. The Pt dopants added to the gas sensitive layer created small clusters on the surface of the WO3 grains. The presence of those additives changes the potential barrier between the metal oxide crystals and caused a decrease of the sensing layer conductance at low dopants concentration, until the exceed of the percolation threshold. Moreover, due to the introduction of additives a change in the activation energy was observed which has influence on the sensor parameters and resulted in increase of the sensitivity to isopropyl alcohol.
Basing on our previous experimental data, together with new results, and on kinetic analysis of the simple model of Pr3+ and Er3+ doped material we present how the maximum phonon value ħωmax can ...change when the non-crystalline matrix under interest (glass) undergoes phase conversion to polycrystalline form (glass-ceramics). We estimate the range of such a change and calculate how this change can affect the luminescence efficiency. The increase in the luminescence efficiency due to diminished value of ħωmax is, for both dopants, at most around 30%. Moreover, the diminishing phonon energy value can sometimes spoil the luminescence efficiency. This seemed to show that the common opinion: that the smaller ħωmax value the better luminescence efficiency, does not have to be true. Therefore we have performed more detailed analysis of the influence of ħωmax on the emission efficiency. It appears that in case of Pr3+ ions there is an optimal maximum phonon energy value (∼420 cm−1) whereas in case of Er3+ ions the value of maximum phonon energy can be of no importance.
•Simple models were used to simulate temperature alterations of the emission spectra of RE3+ ions in glass and glass-ceramics.•The maximum phonon energy value and its changes during phase conversion from the glass to glass-ceramics has been determined.•The luminescent state population as a function of the maximum phonon energy value has been calculated for Pr3+ and Er3+ ions.•For Pr3+ ions there is an optimal phonon energy value, whereas for Er3+ ions the phonon energy value can be of no importance.
Hand-held, portable X-Ray fluorescence instruments (pXRF) provide a means of rapid, in-situ chemical characterisation that has considerable application as a rapid trace evidence characterisation tool ...in forensic geoscience. This study presents both a control test study which demonstrates optimisation of the data collection process, alongside a range of individual forensic case studies, including heavy metal contamination, conflict archaeology, forensic soil characterisation, and verification of human remains, which together validate the technique and provide some comparison between field-based and laboratory-based pXRF applications. Results highlight the time-efficiency and cost-effectiveness of in-situ, field-based pXRF analyses for material characterisation when compared with other trace evidence methods. Analytical precision of various analytes during in-situ analysis was sufficient to demonstrate considerable application of field-based pXRF as a tool for rapid identification of specific areas of interest to be further investigated. Laboratory-based pXRF analyses yielded greater accuracy which could provide an efficient compromise between field-based pXRF and traditional laboratory-based analytical techniques (e.g. WD-XRF, ICP-MS). Further studies should collect more advanced datasets in more diverse locations to further validate the techniques capability to rapidly conduct geochemical surveys in a range of environments.
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•Portable XRF (pXRF) an under-utilised forensic search tool.•Relatively low cost, simple and quick to collect surface data.•Variety of test studies show field and laboratory sample analysis.•Forensic case study examples shown.
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