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The transmission dynamics of highly contagious respiratory diseases like COVID-19 (through coughing/sneezing) is an open problem in the epidemiological studies of such diseases (Bourouiba, JAMA. https://doi.org/10.1001/jama.2020.4756 . 2020). The problem is basically the fluid dynamics of a transient turbulent jet/puff with buoyancy, laden with evaporating droplets carrying the pathogen. A turbulent flow of this nature does not lend itself to reliable estimates through modeling approaches such as RANS (Reynolds-Averaged Navier–Stokes equations) or other droplet-based models. However, direct numerical simulations (DNS) of what may be called “cough/sneeze flows” can play an important role in understanding the spread of the contagion. The objective of this work is to develop a DNS code for studying cough/sneeze flows by a suitable combination of the DNS codes available with the authors (developed to study cumulus cloud flows including thermodynamics of phase change and the dynamics of small water droplets) and to generate useful data on these flows. Recent results from the cumulus cloud simulations are included to highlight the effect of turbulent entrainment (which is one of the key processes in determining the spread of the expiratory flows) on the distribution of liquid water content in a moist plume. Furthermore, preliminary results on the temperature distribution in a “dry cough” (i.e., without inclusion of liquid droplets) are reported to illustrate the large spatial extent and time duration over which the cough flow can persist after the coughing has stopped. We believe that simulations of this kind can help to devise more accurate guidelines for separation distances between neighbors in a group, design better masks, and minimize the spread of respiratory diseases of the COVID-19 type.

In this work, the influence of initial geometric imperfections on geometrically nonlinear free vibrations of thin elastic plates has been investigated by an asymptotic numerical method. The nonlinear strain displacement relationship of von Karman theory is adopted to calculate the elastic strain energy. The harmonic balance approach and Hamilton’s principle are used to convert the equation of motion into an operational formulation. The nonlinear problem is transformed into a sequence of linear ones having the same stiffness matrix, which can be solved by a classical finite-element method. To improve the validity range of the power series, Padé approximants are incorporated and a continuation technique is also used to get the whole solution. Numerical results are discussed and compared to those available in the literature and convergence of the solution is shown for various amplitudes of imperfection.

Bài báo này trình bày một hệ thống bộ chuyển đổi DC-DC tăng cao dựa trên siêu tụ. Hệ thống được đề xuất là sự kết hợp của ngân hàng siêu tụ và các bộ chuyển đổi điện tử công suất. Bộ chuyển đổi DC-DC tăng cao được sử dụng làm giao diện giữa ngân hàng siêu tụ và đầu ra. Các chiến lược điều khiển cho bộ chuyển đổi tăng cao và các mạch cân bằng sạc song song cần thiết cho siêu tụ cũng được trình bày trong bài báo này. Thiết kế bộ điều khiển cho hoạt động vòng kín của bộ chuyển đổi tăng cao được thực hiện bằng phương pháp kiểm soát không gian trạng thái (kiểm soát phản hồi đầu ra). Một nguyên mẫu phần cứng cũng được xây dựng để xác thực hiệu suất của hệ thống được đề xuất một cách thực nghiệm.

The relationship of the flow stress with the strain, strain rate, and temperature is complex and often described by constitutive equations. Constitutive equations are one of the principal inputs for the hot working simulation using finite element method (FEM). The current investigation focuses on predicting the high temperature flow behaviour of Fe-15.9Cr-1.7Mo-0.43C-0.14Nb-0.22N (wt%) nitrogen alloyed martensitic stainless steel using constitutive equations. The flow curves obtained from isothermal hot compression tests conducted in a temperature range of 1173–1423 K and strain rate range of 0.001–10 s−1 were used for modelling. Johnson Cook (JC), Modified Johnson Cook (m-JC) and artificial neural network (ANN) models were employed to formulate the hot deformation behaviour. Accuracy of the predictions was evaluated using parameters such as correlation coefficient (R) and average absolute relative error (AARE). The JC and m-JC models showed AARE of 19.6 and 1.2%, respectively. For developing the ANN model, some of the best training algorithms and transfer functions were explored. Bayesian-regularization employing hyperbolic tangent transfer function gave the best results with AARE of 0.3% and the correlation coefficient of 0.999.

Laser-assisted direct energy deposition (LDED) is an additive manufacturing technology which involves melting/fusion of materials in the form of powder or wire using laser as a focused heat source and its deposition in a layer-by-layer fashion on a dummy substrate to build the product in its final shape by one-step processing. LDED is a very important technology for obtaining component with extreme precision and with minimum loss of material and a flexible one to build component of any kind including metal/alloys, metal matrix composites, and intermetallics. LDED may be categorized in to laser engineered net shaping, laser metal deposition, direct metal deposition, and direct metal printing. In the present contribution, a detailed discussion on the principle of LDED, role of process parameters in influencing the properties, and the present status on the application of LDED for the fabrication of metallic, metal matrix composite, and intermetallics will be discussed in details. Finally, the future scope of research on LDED will be presented.

We demonstrate the sweeping effect in turbulence using numerical simulations of hydrodynamic turbulence without a mean velocity. The velocity correlation function, $$C(\mathbf{k},\tau )$$ , decays with time due to the eddy viscosity. In addition, $$C(\mathbf{k},\tau )$$ shows oscillations due to the sweeping effect by “random mean velocity field” $${ \tilde{\mathbf{U}}}_0$$ . We also perform numerical simulation with mean velocity $$\mathbf{U}_0= 10\hat{z}$$ (10 times the rms speed) for which $$C(\mathbf{k},\tau )$$ exhibits damped oscillations with the frequency of $$|\mathbf{U}_0| k$$ and decay time scale corresponding to the $$\mathbf{U}_0=0$$ case. For $$\mathbf{U}_0=10\hat{z}$$ , the phase of $$C(\mathbf{k},\tau )$$ shows the sweeping effect, but it is overshadowed by oscillations caused by $$\mathbf{U}_0$$ . We also demonstrate that for $$\mathbf{U}_0=0$$ and $$10\hat{z}$$ , the frequency spectra of the velocity fields measured by real-space probes are respectively $$f^{-2}$$ and $$f^{-5/3}$$ ; these spectra are related to the Lagrangian and Eulerian space-time correlations respectively.

Selective laser melting (SLM) provides an opportunity to manufacture parts with complex geometry, minimal wastage, and no need for special tooling. However, the fabricated parts exhibit heterogeneity and anisotropy in mechanical properties and residual stresses, which have been long-term concerns of the SLM of metallic materials. The present study investigates the effect of melting sequence and heat treatment on such heterogeneous and anisotropic properties in the SLM Ti6Al4V alloys. As a relatively low-cost and effective approach, the application of melting sequence led to the homogenization of the microstructure and improvement of mechanical properties, though anisotropy in properties (residual stresses, hardness) remained. The application of the heat treatment process not only homogenized the hardness but also reduced the anisotropy. These approaches would be considered as the two potential strategies to overcome the shortcoming of the SLM process, depending on the required properties, possibility and performance, and the budget.

Nanomaterials have been extensively used to develop potent regenerative medicine against diseased and damaged nervous tissues concerning memory, cognition, and locomotion. The exquisite properties such as mechanical, thermal, and electrical properties of carbon-based nanomaterials (graphene and carbon nanotubes) render them the ability to drive neural tissue repair and regeneration. This review mainly focuses on the importance of carbon nanomaterials and their polymeric composites in nerve tissue engineering applications. Along with that, we also discuss about the properties of the scaffolds, types of materials used, different types of composite preparation methods, and background of synthesis of polymer nanocomposites for neural tissue engineering. Moreover, current limitations of using carbon nanomaterials in tissue engineering are also explored along with the future prospective. Overall, this article reviews carbon nanomaterial-based polymer composites as promising “next-generation” treatment strategies in the area of neural tissue engineering.

Zinc oxide tetrapod whiskers (T-ZnO) with uniform morphology were processed by thermal evaporation and condensation technique. This was used as filler in epoxy matrix resins to formulate room temperature curable, thermally conducting and high-strength composite adhesive systems. Adhesive compositions with varying extend of T-ZnOs were processed and cured using an ambient temperature curable amine hardener. Adhesive formulations which contain the same extent of conventional irregularly shaped zinc oxide particles were also processed for comparison. Various formulations were evaluated for lap shear strength (LSS), thermal conductivity and morphological examinations. Epoxy-TZnO-based adhesive formulations exhibited higher lap shear strength and thermal conductivity compared to their conventional zinc oxide-based counterparts. Thus, an optimized epoxy-TZnO formulation exhibited 42% improvement in LSS and 77% in thermal conductivity than their zinc oxide counterparts. Fracture morphology revealed a rough texture and uniform distribution of T-ZnO in the epoxy resin system.