On a 3D material modelling of smart nanocomposite structures

Smart composites (SCs) are utilized in electro-mechanical systems such as actuators and energy harvesters. Typically, thin-walled components such as beams, plates, and shells are employed as structural elements to achieve the mechanical behavior desired in these composites. SCs exhibit various advanced properties, ranging from lower order phenomena like piezoelectricity and piezomagneticity, to higher order effects including flexoelectricity and flexomagneticity. The recently discovered flexomagneticity in smart composites has been investigated under limited conditions. A review of the existing literature indicates a lack of evaluation in three-dimensional (3D) elasticity analysis of SCs when the flexomagnetic effect (FM) exists. To address this issue, the governing equations will incorporate the term ∂/∂z, where z represents the thickness coordinate. The variational technique will guide us in further developing these governing equations. By using hypotheses and theories such as a 3D beam model, von Kármán's strain nonlinearity, Hamilton's principle, and well-established direct and converse FM models, we will derive the constitutive equations for a thick composite beam. Conducting a 3D analysis implies that the strain and strain gradient tensors must be expressed in 3D forms. The inclusion of the term ∂/∂z necessitates the construction of a different model. It should be noted that current commercial finite element codes are not equipped to accurately and adequately handle micro- and nano-sized solids, thus making it impractical to model a flexomagnetic composite structure using these programs. Therefore, we will transform the derived characteristic linear three-dimensional bending equations into a 3D semi-analytical Polynomial domain to obtain numerical results. This study demonstrates the importance of conducting 3D mechanical analyses to explore the coupling effects of multiple physical phenomena in smart structures

PASSIVE ATMOSPHERIC WATER HARVESTING UTILIZING AN ANCIENT CHINESE INK SLAB

Extraction of atmospheric water using a passive mechanism instead of a complex and advanced equipment has become an emerging subject. There is a clear record in MengxiBitan by Shen Kuo(1031~1095) that an ink slab has the ability to collect water from the air. Its mechanism is exactly similar to the Fangzhu [1], a recently investigated device for atmospheric water harvesting (AWH). Based on the Fangzhu device, a mathematical model for the AWH mechanism in ink slab-like materials is suggested. Using He’s frequency formulation and two-scale fractal derivatives the possible working mechanism of ink slab-like materials is investigated. The potential applications of ink slab-like structures for AWH in interior and exterior architecture are also presented and discussed. It is revealed that efficiency of the slabs highly depends on velocity and temperature of the flowing air and also its low-frequency characteristics

HAMILTONIAN-BASED FREQUENCY-AMPLITUDE FORMULATION FOR NONLINEAR OSCILLATORS

Complex mechanical systems usually include nonlinear interactions between their components which can be modeled by nonlinear equations describing the sophisticated motion of the system. In order to interpret the nonlinear dynamics of these systems, it is necessary to compute more precisely their nonlinear frequencies. The nonlinear vibration process of a conservative oscillator always follows the law of energy conservation. A variational formulation is constructed and its Hamiltonian invariant is obtained. This paper suggests a Hamiltonian-based formulation to quickly determine the frequency property of the nonlinear oscillator. An example is given to explicate the solution process

Right Atrial Thrombus in a COVID-19 Child Treated Through Cardiac Surgery

We herein report a case of large intracardiac thrombus in a child with SARS-CoV-2 infection (COVID-19). The diagnosis of COVID-19 was confirmed through HRCT and RT-PCR. Transthoracic echocardiography revealed a large thrombus in the right atrium treated successfully via cardiac surgery. The underlying mechanisms of this thrombus in the COVID-19 infection may be attributed to the hypercoagulation and inflammatory condition incurred by the COVID-19 virus

On the Vibrations and Stability of Moving Viscoelastic Axially Functionally Graded Nanobeams

In this article, size-dependent vibrations and the stability of moving viscoelastic axially functionally graded (AFG) nanobeams were investigated numerically and analytically, aiming at the stability enhancement of translating nanosystems. Additionally, a parametric investigation is presented to elucidate the influence of various key factors such as axial gradation of the material, viscosity coefficient, and nonlocal parameter on the stability boundaries of the system. Material characteristics of the system vary smoothly along the axial direction based on a power-law distribution function. Laplace transformation in conjunction with the Galerkin discretization scheme was implemented to obtain the natural frequencies, dynamical configuration, divergence, and flutter instability thresholds of the system. Furthermore, the critical velocity of the system was evaluated analytically. Stability maps of the system were examined, and it can be concluded that the nonlocal effect in the system can be significantly dampened by fine-tuning of axial material distribution. It was demonstrated that AFG materials can profoundly enhance the stability and dynamical response of axially moving nanosystems in comparison to homogeneous materials. The results indicate that for low and high values of the nonlocal parameter, the power index plays an opposite role in the dynamical behavior of the system. Meanwhile, it was shown that the qualitative stability of axially moving nanobeams depends on the effect of viscoelastic properties in the system, while axial grading of material has a significant role in determining the critical velocity and natural frequencies of the system

Strain-Gradient Bar-Elastic Substrate Model with Surface-Energy Effect: Virtual-Force Approach

This paper presents an alternative approach to formulating a rational bar-elastic substrate model with inclusion of small-scale and surface-energy effects. The thermodynamics-based strain gradient model is utilized to account for the small-scale effect (nonlocality) of the bar-bulk material while the Gurtin–Murdoch surface theory is adopted to capture the surface-energy effect. To consider the bar-surrounding substrate interactive mechanism, the Winkler foundation model is called for. The governing differential compatibility equation as well as the consistent end-boundary compatibility conditions are revealed using the virtual force principle and form the core of the model formulation. Within the framework of the virtual force principle, the axial force field serves as the fundamental solution to the governing differential compatibility equation. The problem of a nanowire embedded in an elastic substrate medium is employed as a numerical example to show the accuracy of the proposed bar-elastic substrate model and advantage over its counterpart displacement model. The influences of material nonlocality on both global and local responses are thoroughly discussed in this example

Errors in Diagnosing Infectious Diseases: A Physician Survey

Background: Infectious diseases are commonly missed or misdiagnosed. Errors in diagnosing infectious diseases not only affect the patient but also the community health. Objectives: To describe our investigation on the most common errors in diagnosing infectious diseases and their causes according to the physicians' reports. Methods: Between August 2018 and February 2019, specialist physicians and residents across Mashhad, Iran were invited to participate in a survey to report errors they had made or witnessed regarding the diagnosis of infectious diseases. Results: Overall, 465 cases were reported by 315 participants. The most common infectious diseases affected by diagnostic errors were upper respiratory tract infections (URTIs) (n = 69, 14.8%), tuberculosis (TB) (n = 66, 14.1%), pleuro-pulmonary infections (n = 54, 11.6%), central nervous system (CNS) infections (n = 51, 10.9%), and urinary tract infections (n = 45, 9.6%). Errors occurred most frequently in generating a diagnostic hypothesis (n = 259, 55/7%), followed by history taking (n = 200, 43%), and physical examination (n = 191, 41/1%). Errors related to the diagnosis of TB (odds ratio [OR]: 2.4, 95% confidence interval [CI]:0.9–5.7; P value: 0.047) and intra-abdominal infections (OR: 7.2, 95% CI: 0.9–53.8; P value: 0.02) were associated with more-serious outcomes. Conclusion: A substantial proportion of errors in diagnosing infectious diseases moderately or seriously affect patients' outcomes. URTIs, TB, and pleuropulmonary infections were the most frequently reported infectious diseases involved in diagnostic error while errors related to the diagnosis of TB and intraabdominal infections were more frequently associated with poor outcomes. Therefore, contagious and potentially life-threatening infectious diseases should always be considered in the differential diagnosis of patients who present with compatible clinical syndromes

Treatment of two different water resources in desalination and microbial fuel cell processes by poly sulfone/sulfonated poly ether ether ketone hybrid membrane

The PS (Polysulfone)/SPEEK (sulfonated poly ether ether ketone) hybrid membranes were fabricated and modified with low and high DS (degrees of sulfonation) for the desalination of brackish water and proton exchange membrane in microbial fuel cell. The results illustrated that SPEEK has changed the morphology of membranes and increase their hydrophilicity. PS/SPEEK with lower DS (29%) had the rejection percentage of 62% for NaCl and 68% for MgSO4; while it was 67% and 81% for PS/SPEEK (76%) at 4 bars. Furthermore, the water flux for PS at 10 bar was 12.41 L m-2 h-1. It was four times higher for PS/SPEEK (29%) which means 49.5 L m-2 h-1 and 13 times higher for PS/SPEEK (76%) with means 157.76 L m-2 h-1. However, in MFC (microbial fuel cell), the highest power production was 97.47 mW/m2 by PS/SPEEK (29%) followed by 41.42 mW/m2 for PS/SPEEK (76%), and 9.4 mW/m2 for PS. This revealed that the sulfonation of PEEK (poly ether ether ketone) made it a better additive for PS for desalination, because it created a membrane with higher hydrophilicity, better pore size and better for salt rejection. Although for the separator, the degree of sulfonation was limited; otherwise it made a membrane to transfer some of the unwanted ions