Nonlinear analysis of laminated shells with alternating stiff/soft lay-up

This paper proposes a multi-layer formulation for the nonlinear analysis of laminated shells with an alternating stiff/soft lay-up. The zigzag variation of planar displacements is taken into account by adding to the Reissner–Mindlin formulation a specific set of zigzag function which is effective for the considered lay-up. Furthermore, a piecewise linear through-thickness distribution of the material transverse shear strain is assumed, which agrees well with the real distribution. The proposed lamination model with a low-order nonlinear strain–displacement relationship is incorporated within a co-rotational framework for geometric nonlinear analysis, thus upgrading the low-order local element formulation to large displacement analysis with relative ease. In addition, a local shell system is employed for direct definition of the additional zigzag displacement fields and associated parameters, which are thus excluded from the large displacement co-rotational transformations. The application of the proposed laminated shell modelling approach is illustrated in this paper for a 9-noded co-rotational shell element, which utilises the Mixed Interpolation of Tensorial Components (MITC) method in the local system for overcoming locking effects. Several linear and nonlinear numerical examples of multi-layer shell structures with alternating stiff/soft lay-ups are used to illustrate the effectiveness and efficiency of the proposed modelling approach

3-D scattering of obliquely incident Rayleigh waves by a saturated alluvial valley in a layered half-space

In this paper, three-dimensional (3-D) scattering of obliquely incident Rayleigh waves by a saturated alluvial valley embedded in a layered half-space is studied in the frequency domain by using the indirect boundary element method. The total responses are assumed as the sum of the free-field responses and scattered-field responses. The free-field responses are calculated using the direct stiffness method and the scatter-field responses outside and inside of the valley are simulated by applying two sets of fictitious moving distributed loads and pore pressures on the interface of the valley. The amplitudes of the fictitious distributed loads and pore pressures are determined from the boundary conditions. The method is validated by comparing the results with the results published in the literature, and numerical results are obtained for a saturated valley embedded in a uniform saturated half-space and in a single elastic layer overlying elastic half-space. The effects of incident frequency, incident angle, porosity, drainage condition, and soil layers on the dynamic responses are discussed. It is found that 3-D scattering is different from the 2-D case. As the porosity decreased, the pore pressures around the valley became smaller but their oscillations became violent. The wave fields in a layered site are determined by the “dynamic interaction between valley and the layered half-space” and the dispersion characteristics of Rayleigh waves for the given layered-half-space

A hierarchic optimisation approach towards locking-free shell finite elements

A hierarchic optimisation approach is presented for relieving inaccuracies in conforming shell elements arising from locking phenomena. This approach introduces two sets of strain modes: (i) objective strain modes, defined in the physical coordinate system, and (ii) corrective strain modes, representing conforming strains enhanced with hierarchic strain modes. This leads to two alternative families of element, objective and corrective, both arising from minimising the difference between objective and corrective strains. Importantly, the proposed approach not only alleviates shear and membrane locking, but it also addresses locking arising from element distortion. The application of the proposed optimisation approach is demonstrated for a 9-noded quadrilateral Lagrangian shell element, where the membrane, bending and transverse shear strains are separately optimised, all within a local co-rotational framework that extends the element application to geometric nonlinear analysis. Several numerical examples, including cases with geometric and material nonlinearity, are finally presented to illustrate the effectiveness of the optimised 9-noded shell element in relieving the various sources of locking

A detailed analysis of online pharmacy characteristics to inform safe usage by patients

Background: Evidence suggests that consumers potentially put themselves at risk when purchasing medicines on-line. Whilst logos provided by regulators may provide some level of reassurance there may be other indicators which could be used by consumers to identify those websites which may be safely used. Objectives: Identify characteristics of on-line pharmacies which are related to whether websites are regulated or non-regulated and those characteristics which could be used by patients to increase the likelihood of accessing regulated sites. Setting: Online pharmacies which supply diazepam, fluoxetine and simvastatin. Methods: Using piloted search terms via Google and Yahoo search engines, identified websites were screened for regulatory status, adherence to regulatory standards, administrative requirements, clinical assessment requirements and additional details deemed to be of relevance to a user. Characteristics of regulated and non-regulated (defined as those with an absence of a correctly linked regulatory logo) websites were compared to identify differences which could be used to improve patient safety. Main outcome measure: Regulatory status, adherence to regulatory standards, quality of information provision, barriers to medicines access. Results: 113 websites sold diazepam, fluoxetine and simvastatin; were identified within the first 100 results. Less than quarter were found to be regulated online pharmacies. 80 websites were willing to sell the medication without a prescription. The unregulated internet pharmacy websites (defined as those with an absence of a correctly linked regulatory logo) were found to adhere more closely to the clinical criteria, were less significantly likely to disclose a contact name and address, telephone number of the pharmacy or demand a prescription prior to sale (P\0.05, Fisher’s Exact). Conclusions: The three prescription-only medicines which are liable to abuse, have potentially serious interactions and require counselling to ensure patient safety are readily available via the internet. When purchasing medicines via this route UK consumers should be made aware of the importance of regulatory logos and additionally should ensure that the seller can be meaningfully contacted by the contact details provided. The provision of clinical information should not be used alone as an indication of the seller’s provenance

Ispitivanje antioksidativne aktivnosti in vitro polipeptida meduze (Rhopilema esculentum)

Jellyfish gelatin was hydrolyzed by different proteases to obtain antioxidative polypeptides. The gelatin hydrolysate obtained by progressive hydrolysis using trypsin and Properase E exhibited the highest hydrolysis degree and antioxidant activity. Three series of gelatin polypeptides (SCP1, SCP2 and SCP3) were obtained by ultrafiltrating the gelatin hydrolysate through molecular mass cut-off membranes of 10, 6 and 2 kDa, respectively. Amino acid composition analysis showed that SCP3 had the highest total hydrophobic amino acid content. The in vitro antioxidant tests demonstrated that SCP2 had the strongest hydroxyl radical and hydrogen peroxide scavenging activities and metal chelating ability, while SCP3 showed the highest reducing power, antioxidant activity in linoleic acid emulsion system and superoxide anion radical scavenging activity. The results support the feasibility of jellyfish gelatin as a natural antioxidant polypeptide provider, and enzymatic hydrolysis and ultrafiltration could be potent future processing technologies to utilize the abundant jellyfish resource.Hidrolizom želatine iz meduze pomoću različitih proteaza dobiveni su polipeptidi antioksidativnih svojstava. Najveći stupanj hidrolize i najbolja antioksidativna svojstva imao je hidrolizat dobiven progresivnom hidrolizom pomoću tripsina i Properase E. Ultrafiltracijom hidrolizata kroz membrane (10, 6 i 2 kDa) dobivene su tri serije polipeptida želatine: SCP1, SCP2 i SCP3. Analizom aminokiselinskoga sastava ustanovljeno je da SCP3 ima najveći ukupni udio hidrofobnih aminokiselina. Antioksidativni testovi in vitro pokazali su da SCP2 ima najveću sposobnost uklanjanja hidroksilnih radikala i vodikova peroksida te keliranja metala, a SCP3 najveću redukcijsku moć, najbolju antioksidativnu aktivnost u emulzijskom sustavu linoleinske kiseline te sposobnost uklanjanja superoksidnih aniona. Rezultati potvrđuju da se želatina iz meduze može upotrijebiti kao izvor prirodnih antioksidativnih polipeptida, a enzimska hidroliza i ultrafiltracija kao postupci prerade za njezino iskorištavanje

Ispitivanje antioksidativne aktivnosti in vitro polipeptida meduze (Rhopilema esculentum)

Jellyfish gelatin was hydrolyzed by different proteases to obtain antioxidative polypeptides. The gelatin hydrolysate obtained by progressive hydrolysis using trypsin and Properase E exhibited the highest hydrolysis degree and antioxidant activity. Three series of gelatin polypeptides (SCP1, SCP2 and SCP3) were obtained by ultrafiltrating the gelatin hydrolysate through molecular mass cut-off membranes of 10, 6 and 2 kDa, respectively. Amino acid composition analysis showed that SCP3 had the highest total hydrophobic amino acid content. The in vitro antioxidant tests demonstrated that SCP2 had the strongest hydroxyl radical and hydrogen peroxide scavenging activities and metal chelating ability, while SCP3 showed the highest reducing power, antioxidant activity in linoleic acid emulsion system and superoxide anion radical scavenging activity. The results support the feasibility of jellyfish gelatin as a natural antioxidant polypeptide provider, and enzymatic hydrolysis and ultrafiltration could be potent future processing technologies to utilize the abundant jellyfish resource.Hidrolizom želatine iz meduze pomoću različitih proteaza dobiveni su polipeptidi antioksidativnih svojstava. Najveći stupanj hidrolize i najbolja antioksidativna svojstva imao je hidrolizat dobiven progresivnom hidrolizom pomoću tripsina i Properase E. Ultrafiltracijom hidrolizata kroz membrane (10, 6 i 2 kDa) dobivene su tri serije polipeptida želatine: SCP1, SCP2 i SCP3. Analizom aminokiselinskoga sastava ustanovljeno je da SCP3 ima najveći ukupni udio hidrofobnih aminokiselina. Antioksidativni testovi in vitro pokazali su da SCP2 ima najveću sposobnost uklanjanja hidroksilnih radikala i vodikova peroksida te keliranja metala, a SCP3 najveću redukcijsku moć, najbolju antioksidativnu aktivnost u emulzijskom sustavu linoleinske kiseline te sposobnost uklanjanja superoksidnih aniona. Rezultati potvrđuju da se želatina iz meduze može upotrijebiti kao izvor prirodnih antioksidativnih polipeptida, a enzimska hidroliza i ultrafiltracija kao postupci prerade za njezino iskorištavanje

Reduction of train-induced vibrations by using a trench in a layered half-space

A coupled model of a track-layered ground-in-filled trench system is developed to investigate the isolation effects of an in-filled trench on reducing vibrations generated by moving train loads. By using the substructure method, the whole model is decomposed into two parts: the layered ground containing the in-filled trench and the track. Firstly, the flexibility coefficient for moving uniformly distributed loads applied on the layered ground containing the trench is obtained by using the 2.5D indirect boundary element method. Then, the dynamic equilibrium equation of the track under the moving train loads and uniformly distributed loads are established. Finally, the layered ground and the track are coupled according to the equivalence between the deformation of the track and the vertical displacement of the layered ground. The validity of the method is confirmed by comparing its results with the published ones. Numerical calculations are performed by embedding an in-filled trench in a homogenous ground, in a single layered ground and also in the real site at Ledsgard as examples. The results show that the isolation effects are different for different ground conditions and for different geometric parameters such as the depth, width and location of the in-filled trench

Experiment-based simulation of a cross-flow large-scale SOFC model

The multi-physical field full-coupling simulation of solid oxide fuel cell (SOFC) stack requires huge computational resources. Repeated iteration of highly non-linear calculation is easy to cause oscillation and lead to solution failure. At present, the simulation of SOFC stack models mainly focuses on the co-flow condition and counter-flow condition models. Most of them are simplified models that simplify the stack scale or physical field. In this paper, a SOFC decoupling model based on machine learning is established, and the full three-dimensional and multi-physical fields of the cross-flow large-scale SOFC stack are simulated. The model is divided into three parts for calculation, unit cell model, alternative mapping model, and cross-flow large-scale SOFC stack model. The alternative mapping model obtained by the BP neural network algorithm replaces the nonlinear multi-physics equations in the traditional model. Compared with the traditional method, the decoupling model can greatly reduce the computing resources and improve the stability of computing. In this paper, the experimental data of the single cell and the 30-layer stack are used to calibrate and verify the simulation results of stack. Studying the performance of the SOFC stack under different parameter conditions. Temperature, flow uniformity, gas mole fraction, and voltage distribution in the SOFC stack under different inlet flow rates and stack currents are obtained. Obtaining the output power and fuel utilization rate of the stack under different working conditions

Aharonov-Bohm interference in topological insulator nanoribbons

Topological insulators represent novel phases of quantum matter with an insulating bulk gap and gapless edges or surface states. The two-dimensional topological insulator phase was predicted in HgTe quantum wells and confirmed by transport measurements. Recently, Bi2Se3 and related materials have been proposed as three-dimensional topological insulators with a single Dirac cone on the surface and verified by angle-resolved photoemission spectroscopy experiments. Here, we show unambiguous transport evidence of topological surface states through periodic quantum interference effects in layered single-crystalline Bi2Se3 nanoribbons. Pronounced Aharonov-Bohm oscillations in the magnetoresistance clearly demonstrate the coverage of two-dimensional electrons on the entire surface, as expected from the topological nature of the surface states. The dominance of the primary h/e oscillation and its temperature dependence demonstrate the robustness of these electronic states. Our results suggest that topological insulator nanoribbons afford novel promising materials for future spintronic devices at room temperature.Comment: 5 pages, 4 figures, RevTex forma