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The psychological consequences of corona virus disease (COVID- 19) pandemic on health care professionals specially working nurses were serious due to their higher exposure. The aim of this study was to assess the impact of covid-19 pandemic on the mental health among working nurses. This institutional based cross sectional study was conducted at Bangabandhu Sheik Mujib Medical University (BSMMU) Hospital, Dhaka, Bangladesh, from July 2020 to June 2021. A total of 120 nurses, working in different units of BSMMU Hospital were included. Data were collected by face-to-face interview. The depression, anxiety and stress scale- 21 (DASS- 21) was used to assess the psychological impact of COVID- 19 on nurses. The prevalence of depression, anxiety and stress among working nurses was 25.8%, 44.2% and 64.1% respectively. Nurses working in the day shift duties, having no infection prevention training, lack of family support and excess work load were the factors significantly associated with depression (p

Mechanical characterisation of the layer-specific, viscoelastic properties of the human oesophagus is crucial in furthering the development of devices emerging in the field, such as robotic endoscopic biopsy devices, as well as in enhancing the realism, and therefore effectiveness, of surgical simulations. In this study, the viscoelastic and stress-softening behaviour of the passive human oesophagus was investigated through ex vivo cyclic mechanical tests. Due to restrictions placed on the laboratory as a result of COVID-19, only oesophagi from cadavers fixed in formalin were allowed for testing. Three oesophagi in total were separated into their two main layers and the mucosa–submucosa layer was investigated. A series of uniaxial tensile tests were conducted in the form of increasing stretch level cyclic tests at two different strain rates: 1% s$$^{-1}$$ - 1 and 10% s$$^{-1}$$ - 1 . Rectangular samples in both the longitudinal and circumferential directions were tested to observe any anisotropy. Histological analysis was also performed through a variety of staining methods. Overall, the longitudinal direction was found to be much stiffer than the circumferential direction. Stress-softening was observed in both directions, as well as permanent set and hysteresis. Strain rate-dependent behaviour was also apparent in the two directions, with an increase in strain rate resulting in an increase in stiffness. This strain rate dependency was more pronounced in the longitudinal direction than the circumferential direction. Finally, the results were discussed in regard to the histological content of the layer, and the behaviour was modelled and validated using a visco-hyperelastic matrix-fibre model.

Immunoglobulin M (IgM) Nephropathy is a primary glomerulonephritis, characterized by predominant IgM deposition on direct immunofluorescence (DIF) microscopy. Long considered to be similar to minimal change disease (MCD) or focal segmental glomerulosclerosis (FSGS), it is now considered to be a separate entity with unique epidemiology, clinical presentation, biopsy findings, treatment response and prognosis. Although steroid is the first line treatment, there is a high degree of steroid resistance. Other immunosuppressive egents have not been quite effective. Rituximab is an emerging treatment option. We present a 40-year-old man with IgM Nephropathy in whom Rituximab proved to be a highly effective treatment.

In this paper, we study the problem of shape-programming of incompressible hyperelastic shells through differential growth. The aim of the current work is to determine the growth tensor (or growth functions) that can produce the deformation of a shell to the desired shape. First, a consistent finite-strain shell theory is introduced. The shell equation system is established from the 3D governing system through a series expansion and truncation approach. Based on the shell theory, the problem of shape-programming is studied under the stress-free assumption. For a special case in which the parametric coordinate curves generate a net of curvature lines on the target surface, the sufficient condition to ensure the vanishing of the stress components is analyzed, from which the explicit expression of the growth tensor can be derived. In the general case, we conduct the variable changes and derive the total growth tensor by considering a two-step deformation of the shell. With these obtained results, a general theoretical scheme for shape-programming of thin hyperelastic shells through differential growth is proposed. To demonstrate the feasibility and efficiency of the proposed scheme, several nature-inspired examples are studied. The derived growth tensors in these examples have also been implemented in the numerical simulations to verify their correctness and accuracy. The simulation results show that the target shapes of the shell samples can be recovered completely. The scheme for shape-programming proposed in the current work is helpful in designing and manufacturing intelligent soft devices.

Electro-active polymers (EAPs) have the ability to undergo large deformations upon the stimulation by an electric field. They offer new design possibilities\ud in a variety of applications, such as simple soft and flexible actuators, stretchable\ud sensors, and energy harvesters. In the subclass of dielectric elastomers, the operation\ud principle relies on the Coulomb forces between charged electrodes that deform the\ud soft polymer. As the forces are dependent on the permittivity of the dielectric, the addition of filler particles with a high permittivity is a promising approach to increase\ud the overall electro-mechanical coupling. This contribution presents the results of\ud various mechanical and electro-mechanical experiments conducted with the silicone\ud Elastosil P 7670TM filled with Barium-Titanate particles. These experiments are performed in such a fashion that the obtained results are well suited for the identification\ud of the necessary material parameters of an electro-viscoelastic modelling approach\ud in Part II of this contribution (Mehnert et al. Submitted).

Bacterial blight (BB) caused by X. oryzae pv. oryzae is a destructive disease of rice and causes 30-50% losses to rice depending on the outbreak. Development BB resistant rice varieties have long been considered as one of the most effective approach to control the disease. However, the durability of host resistance is breaking down due to the change of pathotypes of X. oryzae pv. oryzae globally. Pathotypic analyses of 239 X. oryzae pv. oryzae Bangladeshi isolates on Near Isogenic Lines (NILs) containing resistance (R) gene (s) revealed the existence of eight pathotypes of X. oryzae pv. oryzae. Among eight pathotypes, pathotypes IV and V were considered as major comprising maximum number of isolates, (30.13% and 23.01%, respectively), whereas pathotype VIII considered as minor consisting only 2.51% of total isolates. Pathotype, I showed highest virulence or aggressiveness compatible with all NILs, whereas pathotype VIII exhibited lowest virulence to these NILs. Bacterial blight resistant genes viz. Xa1 (75.00%), Xa11 (62.50%) and Xa21 (50.00%) showed resistance to most of the pathotypes while Xa4 performed worst as compared to all others R-genes. In pyramid lines, IRBBB63 (Xa5+Xa7+Xa13) and IRBB57 (Xa5+Xa7 +Xa21) showed resistance reaction and IRBB61 (Xa4+Xa5+Xa7), IRBB60 (Xa4+Xa5+Xa13+Xa21), IRBB54 (Xa5+Xa21), and IRBB53 (Xa4+Xa21) showed susceptible reaction to X. oryzae pv. oryzae pathotypes. These results collectively indicated the deployment of Xa1, Xa11, Xa4, Xa5, Xa7, Xa13 and Xa21 either alone or in combination against BB would be a best choice for the development of BB resistant rice varieties in Bangladesh.

Smart photoluminescent nanocomposite surface coating was prepared for simple industrial production of long-persistent phosphorescence and superhydrophobic wood. The photoluminescent nanocomposite coatings were capable to continue emitting light in the dark for prolonged time periods that may reach 1.5 hrs. Difference ratios of lanthanide-doped aluminum strontium oxide (LASO) nanoparticles immobilized into polystyrene (PS) was developed as a nanocomposite coating for wood substrates. To accomplish transparency to the prepared nanocomposite coating, LASO was efficiently dispersed in the form of nano-scaled particles to ensure homogeneous dispersion without agglomeration in the polystyrene matrix. The coated woods showed an absorption band at 374 nm and two emissive bands at 434 and 518. The luminescence spectra showed both long-persistent phosphorescence as well as photochromic fluorescence relying on the LASO ratio. The improved superhydrophobicity and resistance to scratching of the coated woods can be attributed to the LASO NPs incorporated in the polystyrene matrix. In comparison to the uncoated wood substrate, the coated LASO-PS nanocomposite film displayed also photostability and high durability. The current study proved potential high-scale manufacturing of smart wood for a number of applications, such as safety directional signs in buildings, household products, and smart windows.

Dielectric elastomer-based transducers are rapidly gaining importance with the syntheses of new polymers that can potentially be used as dielectric materials. However, these materials are always prone to fracture in the presence of cracks and flaws. Failures originate from flaws (or notches), and a complete fracture may take place due to the propagation of cracks. The present work investigates the crack propagation behavior of two popular polymers, VHB 4910 and Ecoflex, that are widely used as dielectric elastomers. In this case, tensile loadings in laterally constrained boundary conditions are considered. The average crack propagation speed for Ecoflex is higher than that for VHB, implying that Ecoflex will fail earlier than that of VHB under similar conditions. Moreover, with increasing notch lengths at a fixed strain rate, the average crack propagation speed decreases appreciably but becomes constant for comparatively larger notches. The results also conclude that the average crack propagation speed and normalized crack tip diameter remain higher for VHB than for Ecoflex for larger normalized notch lengths. It is observed that the average crack propagation speed increases with strain rates, whereas the normalized crack tip diameter is independent of strain rates. Experimental results obtained here will provide a useful comparative insight to understand the failure behavior of two polymers widely used as dielectric elastomers.

The oesophagus is a primarily mechanical organ whose material characterisation would aid in the investigation of its pathophysiology, help in the field of tissue engineering, and improve surgical simulations and the design of medical devices. However, the layer-dependent, anisotropic properties of the organ have not been investigated using human tissue, particularly in regard to its viscoelastic and stress-softening behaviour. Restrictions caused by the COVID-19 pandemic meant that fresh human tissue was not available for dissection. Therefore, in this study, the layer-specific material properties of the human oesophagus were investigated through ex vivo experimentation of the embalmed muscularis propria layer. For this, a series of uniaxial tension cyclic tests with increasing stretch levels were conducted at two different strain rates. The muscular layers from three different cadaveric specimens were tested in both the longitudinal and circumferential directions. The results displayed highly nonlinear and anisotropic behaviour, with both time- and history-dependent stress-softening. The longitudinal direction was found to be stiffer than the circumferential direction at both strain rates. Strain rate-dependent behaviour was apparent, with an increase in strain rate resulting in an increase in stiffness in both directions. Histological analysis was carried out via various staining methods; the results of which were discussed with regard to the experimentally observed stress-stretch response. Finally, the behaviour of the muscularis propria was simulated using a matrix-fibre model able to capture the various mechanical phenomena exhibited, the fibre orientation of which was driven by the histological findings of the study.

The extreme stretching of dielectric elastomers in sensors, actuators and energy harvesting devices is a common phenomenon where the materials are prone to fracture under the influence of flaws and notches. In this work, we have investigated the length of flaw sensitivities of two widely used dielectric materials, acrylic (VHB) and silicone (Ecoflex) elastomers under a pure shear loading and established that the length of flaw sensitivity of acrylic is almost double than that of silicone. Therefore, the acrylic elastomer is safer to operate for small notches as compared to the silicone material. However, within the flaw-sensitive length, failure stretch, fracture toughness and failure stress are more for Ecoflex than those for VHB. It is found that the failure stretch and the fracture toughness decrease drastically after the length of flaw sensitivities for both materials. Also, the failure stress keeps on decreasing with an increase in notch length for both materials. Afterwards, a simple phenomenological relation is proposed for fitting experimental results under a pure shear loading with only two parameters. The mathematical relation is valid for both the materials and covers the notch sensitivity with a good agreement.

Transparent polyurethane has been widely applied in laminated windshield glasses as the interlayer material to enhance the reliability due to its outstanding impact resistance. Under impact loading such as bird strike, the interlayer undergoes large tensile deformation mainly at intermediate strain rates (at the order of magnitudes from 100 to 103, excluding 1000/s). In addition, the interlayer is on service over a wide range of temperatures for a plane traveling around the world. The mechanical behavior of transparent polyurethane under these conditions is not fully understood. In this study, systematical experiments were performed on transparent polyurethane. The viscoelasticity of the material was firstly verified by several quasi-static cyclic tests. Then a series of large tensile deformation and tensile failure experiments were conducted under intermediate strain rates and at temperatures of − 40 ° C to 40 ° C using a servo-hydraulic high-speed tensile machine. All strain data were acquired by the DIC technique. The experimental results show that tensile stress–strain curves and failure behaviors are significantly temperature and strain rate dependent. The rate-temperature equivalence was also observed. Finally, a phenomenological analysis of mechanical quantities of the material was carried out.

Technological advancements in the field of robotics have led to endoscopic biopsy devices able to extract diseased tissue from between the layers of the gastrointestinal tract. Despite this, the layer-dependent properties of these tissues have yet to be mechanically characterised using human tissue. In this study, the ex vivo mechanical properties of the passive muscularis propia layer of the human oesophagus were extensively investigated. For this, a series of uniaxial tensile tests were conducted. The results displayed hyperelastic behaviour, while the differences between loading the tissue in both the longitudinal and circumferential directions showcased its anisotropy. The anisotropy of the muscular layer was present at different strain rates, with the longitudinal direction being consistently stiffer than the circumferential one. The circumferential direction was found to have little strain-rate dependency, while the longitudinal direction results suggest pronounced strain-rate-dependent behaviour. The repeated trials showed larger variation in terms of stress for a given strain in the longitudinal direction compared to the circumferential direction. The possible causes of variation between trials are discussed, and the experimental findings are linked to the histological analysis which was carried out via various staining methods. Finally, the direction-dependent experimental data was simulated using an anisotropic, hyperelastic model.

Residual stresses may exist in different finitely deformed soft multifunctional materials such as in electro-active and magneto-active polymers. In order to develop accurate constitutive frameworks of these smart materials experiencing electro-magneto-mechanically coupled loads, the presence of residual stresses needs to be considered on the onset of the model development. In this contribution, a spectral constitutive equation for finite strain magneto-electric soft material bodies with residual stresses is developed using spectral invariants, where each spectral invariant has a clear physical meaning. A prototype total energy function comprising of single-variable functions is proposed; a single-variable function that depends on an invariant with a direct meaning is easily handled and is experimentally attractive. Results of some boundary value problems are given.

The effects of addition of magnetic nanoparticles (MNPs) in core-shell hybrid magnetorheological elastomers (MREs) are reported in this study. The main idea of a core-shell hybrid MREs was demonstrated in our previous paper (Bastola et al., 2019). It is observed in the current study that the MNPs enhanced the rheological properties of the suspension in magnetorheological fluid including the improvement of the sedimentation behaviour. Furthermore, magneto-active nanoparticles substantially improved the magnetorheological response of the core-shell hybrid MRE composites.

A comprehensive experimental study performed under a combination of thermo-electro-mechanical loads applied to a widely used electro-active polymer, is presented in the Part I of this work (Mehnert et al., 2021). Soft polymeric materials, used as base materials in electro-active polymers, are highly susceptible to temperature changes. Hence, thermal influences on their behavior have to be investigated precisely. Constitutive modeling and numerical simulation of electro-active polymers are active fields of current research. However, on the one hand, their experimental study under complex loading conditions is non-trivial. On the other hand, very few constitutive modeling approaches meet with experimental data obtained from thermo-electro-mechanical loading conditions. In this contribution, we aim to develop a thermo-electro-mechanically coupled model, which will closely replicate the response of an electro-active polymer investigated under a combination of thermal, electric and mechanical loads. Once the model is calibrated with the experimental data described in Part I of this contribution, it is validated with a different set of data, which shows excellent agreement with experimental findings.