Aerodynamics and aerosol transportation in human airways

Master'sMASTER OF ENGINEERIN

Novel Electrostatic Characterization of Pharmaceutical Powders

Ph.DDOCTOR OF PHILOSOPH

A contribution to understanding the rheological measurement, yielding mechanism and structural evolution of fresh cemented paste backfill

Cemented paste backfill (CPB) is an efficient and sustainable technology for the disposal of tailings in mining industry. However, the flowability of CPB is not completely clear due to the lack of robust characterization methods and sufficient studies. In this study, the effects of pre-shear rate and time, resting time, and shear protocol on the rheological measurements of fresh CPB were examined. Additionally, a yielding model was built, and the 2-h structural evolution was investigated. The structural evolution of CPB was observed using the oscillatory shear rheology method. The underlying mechanisms were investigated using zeta potential, thermogravimetry, ionic concentration, focused beam reflectance measurement, and 1H nuclear magnetic resonance. The pre-shear rate of 100 s−1, pre-shear time of 100 s, pre-shear resting period of 150 s and the stress ramp-up protocol were all recommended by the results. The dual yielding properties of CPB are adequately represented by the proposed model. It is possible to categorize the structural evolution of CPB at rest into three stages, each of which can be attributed to flocculation brought on by particle interactions, packing density enhancement from the massive formation of rigid links, and an increase in the volume fraction of solid, respectively.</p

Crystallizing Micronized Particles of a Poorly Water-Soluble Active Pharmaceutical Ingredient: Nucleation Enhancement by Polymeric Additives

Antisolvent precipitation aided by polymeric additives has increasingly been explored as a method to produce micron-sized/submicron particles of active pharmaceutical ingredients with low aqueous solubilityso as to enhance their dissolution rate and absorption efficiency. This work is aimed toward understanding the role of these additives in mediating crystal nucleation and the growth process. Nucleation kinetics of naproxen, a poorly water-soluble drug, from an ethanol–water solvent mixture at various solute concentrations and in the presence of additives such as polyvinylpyrolidone (PVP) and hydroxypropyl methyl cellulose (HPMC) was investigated. At a given supersaturation, the crystal nucleation rate was calculated from probability distribution of the induction times measured in stirred, small-volume batch solutions. The analysis revealed that PVP additive significantly promotes the nucleation kinetics in the entire range of supersaturation examined, whereas the effect of HPMC on the nucleation kinetics is supersaturation-dependent. Furthermore, the nucleation rates determined as a function of supersaturation followed the trend predicted using the classical nucleation theory (CNT) and indicated the occurrence of heterogeneous nucleation. Thermodynamic and kinetic parameters derived from the CNT equation, together with the crystal habit and size data, were used to elucidate the mechanisms underpinning the effect of polymeric additives on nucleation kinetics

Experimental and modeling study on the transient flow and time-dependent yield stress of superfine-tailings cemented paste backfill

The fresh superfine-tailings cemented paste backfill (SCPB) exhibits strong thixotropy, but quantification of the resulting transient flow (non-steady state) and time-dependent yield stress is lacking. In this study, a simple qualitative model was developed to describe the transient flow and time-dependent yield stress of SCPB. The effect of pre-shear time on the rheological behavior of SCPB was investigated. In addition, the adaptability of conventional non-Newtonian rheological models to SCPB was also evaluated. The results showed the Herschel-Bulkley model provides the most stable dynamic yield stress estimation of SCPB compared to the Bingham and modified Bingham models. A longer pre-shear time (within 500 s) led to smaller initial static yield stress and delayed recovery kinetics of static yield stress, but hardly affected the steady state of SCPB and the time required to reach it. The proposed model provides a good quantification of the transient flow at a given shear rate and time-dependent yield stress of SCPB.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Rivers, Ports, Waterways and Dredging Engineerin

An integrated photonic chip of measurement-device independent quantum key distribution (MDI-QKD)

An integrated chip of MDI-QKD system is demonstrated. The system generates a key rate per pulse of 2.923 × 10^-6 over a distance corresponding to 50-km optical fibre with 25% detection efficiency.Ministry of Education (MOE)National Research Foundation (NRF)Accepted versionThis work was supported by the Singapore Ministry of Education (MOE) Tier 3 grant (MOE2017-T3-1-001), the Singapore National Research Foundation (NRF) National Natural Science Foundation of China (NSFC) joint grant (NRF2017NRF-NSFC002-014) and the Singapore National Research Foundation under the Competitive Research Program (NRF-CRP13-2014-01)

Chip-based measurement-device-independent quantum key distribution using integrated silicon photonic systems

Measurement-device-independent (MDI) quantum key distribution (QKD) employs an untrusted relay to prevent the receiver from side-channel attacks commonly encountered in earlier QKD protocols. Conventional MDI QKD systems rely entirely on bulky and expensive optical setups that present great challenges for system scaling and integration. In this work, an all-chip-based MDI QKD system including two transmitter chips and one server chip is demonstrated using integrated silicon photonic technology. The system is capable of generating polarization-encoded weak coherent states with polarization extinction ratios of over 20 dB, sufficient for low-error MDI QKD. In the proof-of-concept experiment, the chip-based MDI QKD system generates a key rate per pulse of 2.923×10−6 over a distance corresponding to a 50-km standard fiber with 25% detection efficiency and a predicted distance of 120 km with 85% detection efficiency. Our proof-of-concept prototype makes a giant step forward towards fully chip-based MDI QKD systems and highly integrated quantum communication networks in the near future with its high scalability and cost effectiveness.Ministry of Education (MOE)National Research Foundation (NRF)Published versionThis work is supported by the Singapore Ministry of Education (MOE) Tier 3 grant (No. MOE2017-T3-1-001), the Singapore National Research Foundation (NRF) National Natural Science Foundation of China (NSFC) joint grant (No. NRF2017NRF-NSFC002-014), and the Singapore National Research Foundation under the Competitive Research Program (No. NRF-CRP13-2014-01)

Anomalous particle size shift during post-milling storage

10.1007/s11095-007-9497-8Pharmaceutical Research2551175-1185PHRE

Effect of Milling on DSC Thermogram of Excipient Adipic Acid

The purpose of this research was to investigate why and how mechanical milling results in an unexpected shift in differential scanning calorimetry (DSC) measured fusion enthalpy (∆fusH) and melting point (Tm) of adipic acid, a pharmaceutical excipient. Hyper differential scanning calorimetry (hyper-DSC) was used to characterize adipic acid before and after ball-milling. An experimental study was conducted to evaluate previous postulations such as electrostatic charging using the Faraday cage method, crystallinity loss using powder X-ray diffraction (PXRD), thermal annealing using DSC, impurities removal using thermal gravimetric analysis (TGA) and Karl Fischer titration. DSC thermograms showed that after milling, the values of ∆fusH and Tm were increased by approximately 9% and 5 K, respectively. Previous suggestions of increased electrostatic attraction, change in particle size distribution, and thermal annealing during measurements did not explain the differences. Instead, theoretical analysis and experimental findings suggested that the residual solvent (water) plays a key role. Water entrapped as inclusions inside adipic acid during solution crystallization was partially evaporated by localized heating at the cleaved surfaces during milling. The correlation between the removal of water and melting properties measured was shown via drying and crystallization experiments. These findings show that milling can reduce residual solvent content and causes a shift in DSC results