Analysis of floating refuse along the Gombak River

Data were collected on the types and weights of floating refuse along the Gombak River off Jalan Sentul in Kuala Lumpur over a period of 6 months. Based on the samples taken, the refuse was divided into different categories and their proportions by weight and average bulk density were estimated. It was found that the largest component by weight (42%) of the refuse consisted of cans, containers and other products made from metal. The average bulk density of the wet refuse was about 100 kg/m 3 . Suggestions are also made with regards to the best methods to collect the floating refuse and to clean up the rivers in the Kuala Lumpur City area based on the characteristics of the waste and an assessment of the various methods being currently tested

The onset of convection caused by buoyancy during transient heat conduction in deep fluids

The onset of convection in a thermal layer generated by transient heat conduction in deep fluid is examined. It is generally accepted that buoyancy driven convection predominates in deep fluids while surface tension driven convection can occur only in very thin layers of liquid. The occurrence of buoyancy convection can be predicted from conventional linear stability analysis for steady-state heat conduction. Its results are summarised in terms of critical Rayleigh numbers. The point of instability in transient heat conduction is, however, less well understood. Its onset in deep fluids is determined by the mode and rate of cooling. In this paper, the judicial application of transient heat conduction equations and a newly defined transient local Ra with the appropriate boundary conditions has allowed the tracking of the time and spatial development of local hydrodynamic equilibrium to the point of instability. The onset of convection can be predicted from the maximum transient Ra whose values are the same as those previously obtained by linear stability analysis for the same boundary conditions. The critical times and critical depths for stable diffusion in fluids (i.e. without convection) can thus be determined accurately. Agreement with observed values from the literature is very good. The mode and rate of heat conduction are confirmed to be the controlling factors in determining the time of onset of convection

Onset of natural convection in gas-gas system induced by bottom-up transient mass diffusion

The onset of convection induced by transient mass diffusion in a stationary gas was succesfully predicted with transient instability theory and simulated using a computational fluid dynamics (CFD) scheme. 2D time-dependent simulations were conducted for bottom-up diffusion of a light gas in a stagnant heavy gas. The results of simulations were used to calculate the transient Rayleigh number adopted from the theory of Tan and Thorpe (1996 and 1999). The average transient maximum Rayleigh number from simulations is 707, which is close to the theoretical value of 817 for analogous bottom heating with constant heat flux. The simulated critical times of the onset of convection were in reasonably good agreement with the predicted values from theory

On predicting mantle mushroom plumes

AbstractThis study investigates the mechanism of formation of convection plumes of mushroom shape in sub-solidus mantle and their prediction. The seismic-tomographic images of columnar structures of several hundreds kilometers in diameter have been reported by several researchers, while the much cherished mushroom-shaped plume heads could only be found in computational geodynamics (CGD) models and simple small-scale laboratory analogue simulations. Our theory of transient instability shows that the formation of convection plumes is preceded by the onset of convection caused by unsteady-state heat conduction at the boundaries, from which filamentous plumes first appear. The plumes generated at the Core Mantle Boundary (CMB) and lithosphere rising and falling through the mantle have been predicted simply with our theory for various heat fluxes and viscosities, which still remain uncertain amongst geoscientists. The sizes of mushroom plumes in the sub-solidus mantle caused by heat fluxes of 20 and 120 mW/m2 at the CMB are found to be 1842 km and 1173 km with critical times over 825 Myr and 334 Myr respectively. They are comparable to some large continental flood basalt provinces, and they number between 17 and 41. The thickness of the thermal boundary layers at the CMB from which convection plumes evolved are found to be 652 km and 415 km for 20 and 120 mW/m2 respectively.Top cooling may produce plunging plumes of diameter of 585 km and at least 195 Myr old. The number of cold plumes is estimated to be 569, which has not been observed by seismic tomography or as cold spots. The cold plunging plumes may overwhelm and entrap some of the hot rising plumes from CMB, so that together they may settle in the transition zone

Onset of natural convection induced by bottom-up transient mass diffusion in porous media

The theory of convection induced by transient mass diffusion in porous media is advanced and verified by computational fluid dynamics (CFD) simulation. A theory of the onset of buoyancy convection and a new transient Rayleigh number were derived. 2D time-dependent simulations were conducted for bottom–up diffusion of methane gas in a porous medium pre-saturated with air. Sand particles with diameter ranged from 0.003 to 0.006 m were used as the porous media. The average maximum transient Rayleigh number for the onset of convection in the simulations was found to be 29.7, which was quite close to the theoretical value of 27.1. The critical times, critical depths of gas penetration and wavelengths were predicted accurately. It was found that the mass transfer may be driven by simultaneous diffusion and buoyancy convection after the onset. The rate of mass transfer for the convection phase was over three times that of pure diffusion

The effect of mechanical grinding on the mesoporosity of steam-activated palm kernel shell activated carbons

Background: Palm kernel shell activated carbon (OPSA) produced by steam gasification at high temperatures generally results in high surface areas of 1146 to 1600 m2 g−1, attributed to the high volume of micropores (0.43 to 0.56 cm3 g−1). The mesoporosity of naturally occurring activated carbons is observed to increase with decreasing particle size. Mechanical grinding was therefore performed to investigate its effect on the mesoporosity and microporosity of OPSA. Results: Mechanical grinding had a strong effect on mesopore volume and average pore diameter, with an increase in mesopore volume from 47 to 66% as particle size decreases. Interestingly, no significant effect on the micropore fraction was observed in ground OPSA particles. Conclusions: The mechanically ground OPSA particles possessed dual adsorption capabilities due to the high microporosity and moderate mesoporosity contained in the structures. This results in interesting porosity behaviour of palm kernel shell activated carbons and the potential to provide materials of distinct sorption capacities with minimal treatment

On the onset of incipient fluidization

The onset of incipient fluidization is investigated theoretically and simulated by a computational fluid dynamics (CFD) procedure. The onset of incipient instability in a particle bed is preceded by stable gas diffusion in the interstices and is caused by a critical momentum force that may overcome the inertia of the particles. The critical momentum force is provided by the critical superficial gas velocity Uc in the form of critical mass flux of diffusion. It is found that the first movement of particles may be predicted by a critical transient Rayleigh number determined by a critical superficial velocity equals to the minimum fluidization velocity, Umf. The onset of incipient fluidization was found to occur at a critical transient Rayleigh number of 3.1, which is close to the lowest theoretical value for buoyancy convection in a porous medium bounded by free surfaces. Consequently the onset times of incipient fluidization may be predicted accurately. The finding has been found to be supported by the present CFD study, past experiments and simulations in the literature

On predicting mantle mushroom plumes

This study investigates the mechanism of formation of convection plumes of mushroom shape in sub-solidus mantle and their prediction. The seismic-tomographic images of columnar structures of several hundreds kilometers in diameter have been reported by several researchers, while the much cherished mushroom-shaped plume heads could only be found in computational geodynamics (CGD) models and simple small-scale laboratory analogue simulations. Our theory of transient instability shows that the formation of convection plumes is preceded by the onset of convection caused by unsteady-state heat conduction at the boundaries, from which filamentous plumes first appear. The plumes generated at the Core Mantle Boundary (CMB) and lithosphere rising and falling through the mantle have been predicted simply with our theory for various heat fluxes and viscosities, which still remain uncertain amongst geoscientists. The sizes of mushroom plumes in the sub-solidus mantle caused by heat fluxes of 20 and 120 mW/m2 at the CMB are found to be 1842 km and 1173 km with critical times over 825 Myr and 334 Myr respectively. They are comparable to some large continental flood basalt provinces, and they number between 17 and 41. The thickness of the thermal boundary layers at the CMB from which convection plumes evolved are found to be 652 km and 415 km for 20 and 120 mW/m2 respectively. Top cooling may produce plunging plumes of diameter of 585 km and at least 195 Myr old. The number of cold plumes is estimated to be 569, which has not been observed by seismic tomography or as cold spots. The cold plunging plumes may overwhelm and entrap some of the hot rising plumes from CMB, so that together they may settle in the transition zone

Porosity characteristics and pore developments of various particle sizes palm kernel shells activated carbon (PKSAC) and its potential applications

The adsorption behaviour and the micro- and mesopore size distributions of commercial palm kernel shell activated carbons (PKSAC) and other commercial activated carbon are characterized. The results showed that PKSAC are predominantly microporous materials, where micropores account 68–79% of total porosity. On the other hand, commercial activated carbons: Norit SX Plus, Calgon 12×40, and Shirasagi “A” activated carbons contained high mesopore fraction ranging from 33 to 52%. The analysis showed that the degree of mesoporosity of PKSAC is increased steadily with the decrease of particle size. This is due to the presence of channels interconnect the smaller pores in the interior of smaller particle size PKSAC. The smaller size PKSAC particle that is highly mesoporous has preformed better on the adsorption of larger molecules such as methylene blue. On the other hand, bigger size PKSAC particle has better performance on the adsorption of smaller adsorbates such as iodine

The cellular characterization of SARS-CoV-2 spike protein in virus-infected cells using the receptor binding domain binding specific human monoclonal antibodies

A human monoclonal antibody panel (PD4, PD5, PD7, SC23, and SC29) was isolated from the B cells of convalescent patients and used to examine the S protein in SARS-CoV-2-infected cells. While all five antibodies bound conformational-specific epitopes within SARS-CoV-2 spike (S) protein, only PD5, PD7, and SC23 were able to bind to the receptor binding domain (RBD). Immunofluorescence microscopy was used to examine the S protein RBD in cells infected with the Singapore isolates SARS-CoV-2/0334 and SARS-CoV-2/1302. The RBD-binders exhibited a distinct cytoplasmic staining pattern that was primarily localized within the Golgi complex and was distinct from the diffuse cytoplasmic staining pattern exhibited by the non-RBD-binders (PD4 and SC29). These data indicated that the S protein adopted a conformation in the Golgi complex that enabled the RBD recognition by the RBD-binders. The RBD-binders also recognized the uncleaved S protein, indicating that S protein cleavage was not required for RBD recognition. Electron microscopy indicated high levels of cell-associated virus particles, and multiple cycle virus infection using RBD-binder staining provided evidence for direct cell-to-cell transmission for both isolates. Although similar levels of RBD-binder staining were demonstrated for each isolate, SARS-CoV-2/1302 exhibited slower rates of cell-to-cell transmission. These data suggest that a conformational change in the S protein occurs during its transit through the Golgi complex that enables RBD recognition by the RBD-binders and suggests that these antibodies can be used to monitor S protein RBD formation during the early stages of infection. IMPORTANCE: The SARS-CoV-2 spike (S) protein receptor binding domain (RBD) mediates the attachment of SARS-CoV-2 to the host cell. This interaction plays an essential role in initiating virus infection, and the S protein RBD is therefore a focus of therapeutic and vaccine interventions. However, new virus variants have emerged with altered biological properties in the RBD that can potentially negate these interventions. Therefore, an improved understanding of the biological properties of the RBD in virus-infected cells may offer future therapeutic strategies to mitigate SARS- CoV-2 infection. We used physiologically relevant antibodies that were isolated from the B cells of convalescent COVID-19 patients to monitor the RBD in cells infected with SARS-CoV-2 clinical isolates. These immunological reagents specifically recognize the correctly folded RBD and were used to monitor the appearance of the RBD in SARS-CoV-2-infected cells and identified the site where the RBD first appears.Nanyang Technological UniversityPublished versionThe work was supported by DSO National Laboratories and Nanyang Technological University