Impact of Covid-19 on Liquidity, Profitability, and Financial Health: A case study of 3 sectors from Stock Exchange of Thailand

Purpose-To test the impact of Covid-19 pandemic on Profitability, Liquidity, and Financial Health on the selected 3 sectors which are Tourism and Leisure Sector, Transportation and Logistics Sector, and Health Care Service Sector of the Stock Exchange of Thailand. Design/methodology/approach-The author uses Wilcoxon MEAN and MEDIAN tests to test the statistically difference between the financial ratios from year 2019 and 2020. The 10 independent variables of financial ratios are ROA, ROE, Net Profit Margin, Acid Test, Current Ratio, Cash Ratio, Operating Cash Flow Ratio, Total Asset Turnover, Debt to Assets Ratio, Debt to Equity Ratio. Findings-The result confirms the hypothesis that there is a significantly different in the result of Tourism and Leisure Sector on ROA, ROE, Net Profit Margin, and Total Asset Turnover. Which represent the dramatically impact of covid-19 on the Profitability and Financial Health of the firm. While there are not significantly different in Transportation and Logistic Sector and Health Care Sector. Research implications-Researcher can use this Wilcoxon test in other sectors Thailand or in other country. The investors are not recommended to invest in the stock under the sector of tourism and leisure sector due to the financial performance which effected by the covid-19 pandemic. However, investors who concentrate on long-term investing in securities may get beneficial opportunities by using the information to forecast the firm’s position and direction. The investors should not be so panic about the performance of companies in other sectors because the financial performances of the companies in those sectors have not been significantly changed from covid-19 pandemic

The permeability of virtual macroporous structures generated by sphere packing models: comparison with analytical models

Realistic porous structures typical of those made by replication of packed beds of spherical particles have been produced by a novel modelling method. Fluid dynamics simulation of the permeability of these structures agrees well with experimental measurements and similar modelling of structures derived from X-ray tomographic images. By varying the model structures the “bottleneck” flow concept proposed by analytical models in the literature was substantiated, confirming the high dependence of permeability on the size of the windows connecting the pores but also highlighting the need for accurate determination of the connectivity of the pores for these models to be accurate

Discrete element modelling of the packing of spheres and its application to the structure of porous metals made by infiltration of packed beds of NaCl beads

A numerical model, using the discrete element method, has been developed to quantify specific parameters that are pertinent to the packing behaviour of relatively large, spherical NaCl beads and mixtures of beads of different sizes. These parameters have been compared with porosity and connectivity measurements made on porous aluminium castings made by molten metal infiltration into packed beds of such beads, after removal of the NaCl by dissolution. DEM has been found to accurately predict the packing fraction for salt beads with both mono and binary size distributions and from this the pore fractions in castings made by infiltration into packed beds of beads could be predicted. Through simple development of the condition for contacting of neighbouring beads, the number of windows linking neighbouring pores, and their size, could also be predicted across a wide range of small bead additions. The model also enables an insight into the mixing quality and changes in connectivity introduced through the addition of small beads. This work presents significant progress towards the delivery of a simulation based approach to designing preform architectures in order to tailor the resulting porous structures to best suit specific applications

Porous titanium manufactured by a novel powder tapping method using spherical salt bead space holders: characterisation and mechanical properties

Porous Ti with open porosity in the range of 70–80% has been made using Ti powder and a particulate leaching technique using porous, spherical, NaCl beads. By incorporating the Ti powder into a pre-existing network of salt beads, by tapping followed by compaction, salt dissolution and “sintering”, porous structures with uniform density, pore and strut sizes and a predictable level of connectivity have been produced, showing a significant improvement on the structures made by conventional powder mixing processes. Parts made using beads with sizes in the range of 0.5-1.0 mm show excellent promise as porous metals for medical devices, showing structures and porosities similar to those of commercial porous metals used in this sector, with inter-pore connections that are similar to trabecular bone. The elastic modulus (0.86GPa) is lower than those for commercial porous metals and more closely matches that of trabecular bone and good compressive yield strength is retained (21MPa). The ability to further tailor the structure, in terms of the density and the size of the pores and interconnections has also been demonstrated by immersion of the porous components in acid

Assessing the potential for multi-functional “hybrid” porous Al-phase change material structures

This study reports the potential for porous aluminium structures, containing porosity in the region of 50–80%, to provide enhancement of the rate of energy capture in phase change materials, whilst being capable of providing a basic mechanical function. The energy stored and the time for thermal exchange between warm water (at 65 °C) and porous aluminium, pure PCM and an Al-PCM hybrid structure was measured. It was observed that the melting of the PCM within the hybrid structure can be greatly accelerated by the continuous, porous aluminium structure. The energy uptake per second was found to follow an approximately linear dependence on the thermal effusivity for the material. This knowledge was used to predict the potential for enhancement of the rate of energy capture, by varying the porosity in the structure, whilst also estimating the detriment to the energy storage density and the mechanical strength. Appreciating this trade off in performance and properties is vital to the design of multi-functional porous structures

Measurement and simulation of pressure drop across replicated porous aluminium in the Darcy-Forchheimer regime

Experimental measurements of the pressure drop across porous metals have been compared with computational fluid dynamics simulations, for the first time, for structures typified by large pores with small interconnecting “windows”. Structural information for the porous structures was obtained from X-ray computed tomography and a robust methodology for developing a representative volume element is described. The modelling approach used was able to reliably predict the pressure drop behaviour within the Forchheimer regime. The methodology was extended to simulate flow through geometrically-adapted, “semi-virtual” pore structures and this approach could prove to be an invaluable tool in the design of porous metal components for applications involving fluid flow

The manufacture and characterisation of aluminium foams made by investment casting using dissolvable spherical sodium chloride bead preforms

This project sought to design, implement and evaluate a process for the manufacture of porous, spherical salt beads, in order to enhance the reproducibility in mechanical properties of open cell aluminium foams made by a replication-based manufacturing technique. Porous beads were favoured in order to increase the dissolution rate of the salt from the preform, thereby making the manufacture of large foam parts practical. Salt beads were made by a novel method using fine NaCI powder, flour and water to make a paste that was subsequently disintegrated into large beads by mechanical stirring in oil. The NaCI paste viscosity was found to be important to the production of spherical beads and by varying the intensity of mechanical disintegration of the paste, control of the bead size was possible. The salt beads with sizes from 0.5 to 3 mm diameter were compacted into preforms and made into moulds for infiltration with molten pure aluminium by pressure- assisted investment casting. The heat treatment used to "cure" the plaster mould containing the preform was sufficient to remove the flour from the beads, sinter the preform and increase its strength. The effect of preform compaction conditions on the size, shape and volume fraction of porosity was quantified using a number of techniques, including mercury porosimetry, which was used to model the infiltration process. At the highest infiltration pressure 0.25 MPa (2.5 bar) the resulting foam densities were higher, but led to extensive penetration of molten aluminium into the porous beads, slowing down salt removal. In general, the compression strength increased with increasing foam density, and was highly reproducible, but where metal infiltration into the beads was extensive, the foam density increased but with little improvement in the compressive strength.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The Manufacture and Characterisation of Aluminium Foams Made by Investment Casting Using Dissolvable Spherical Sodium Chloride Bead Preforms

Open cell Al foams have been made by infiltrating molten Al into preforms made from porous salt spheres. Infiltration has been effected using simple pressure-assisted vacuum investment casting where the maximum infiltration pressure difference was less than 36 psi. The preform and resulting foam density decreased with increasing compaction pressure and the foam density increased with increasing infiltration pressure. For low pressure infiltration, and high density preforms, salt dissolution was rapid due to the porous nature of the salt spheres. Infiltration of molten Al occurred into the beads and, for high density preforms and higher infiltration pressures, the volume of metal in the beads exceeded that in the cell walls, drastically decreasing the NaCl dissolution rate. A simple approach is shown whereby the data from mercury porosimetry can be used to predict the resulting foam density, thereby aiding the design of preform and beads structures

Characterisation and Mechanical Testing of Open Cell Al Foams Manufactured by Molten Metal Infiltration of Porous Salt Bead Preforms: Effect of Bead Size

Preforms made from porous salt beads with different diameters (0.5–1.0, 1.4–2.0 and 2.5–3.1 mm) have been infiltrated with molten Al to produce porous structures using pressure-assisted vacuum investment casting. Infiltration was incomplete for preforms with high densities. At higher infiltration pressures, penetration of molten Al occurred into beads of all sizes and was predicted using a simple model. The yield strength of the porous structures increased with increasing density and decreasing pore (bead) size. Despite the non-optimum distribution of metal in the porous structure, due to partial infiltration within the beads, the magnitude and density dependence of the yield stress were comparable with those for pure Al foams reported in similar studies. The structural efficiency was improved for structures produced at lower infiltration pressure, where the metal is predominantly distributed in the cell walls. The rate of salt dissolution from the preforms was high, in particular for high density preforms, large beads and preforms infiltrated at low pressures, owing to the ability of the porous beads to collapse as well as dissolve

Structure-property-processing relationships for stainless steel foams made by mechanical aeration of powder slurries

A simple process, based on the mechanical aeration of a powder slurry, followed by gel casting and sintering, has been used to produce 316L stainless steel metal foams. The foams have spherical pores, with a small size range, connected by windows, to create an interconnected, open cell structure. Despite the simplicity of the process, the foams have good and reproducible foam structures and compressive mechanical properties, although the ability to vary the pore size and density is limited. While foams of this type are more likely to be suited to applications where the connected nature of the porosity is exploited, they demonstrate mechanical properties on a par with foams and porous metals specifically suited to structural applications, where specific strength and energy absorption are paramount. Foams made in this way therefore demonstrate the multi-functionality that is required of them if they are to be exploited and are thus exciting prospects for further development. A simple process, based on the mechanical aeration of a powder slurry, followed by gel casting and sintering, has been used to produce stainless steel metal foams. The foams have spherical pores, connected by windows, to create an interconnected, open cell structure. Despite the simplicity of the process, the foams have good and reproducible foam structures and compressive mechanical properties