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Compression-induced electrical percolation and enhanced mechanical properties of polydimethylsiloxane-based nanocomposites
No full textYesIn this work, a compression-induced percolation threshold was found when the thickness of polydimethylsiloxane (PDMS) nanocomposite samples was reduced via a spatial confining forced network assembly (SCFNA) process from 1.0 mm to 0.1 mm. Such as for PDMS/2 wt% short carbon fiber/4 wt% carbon nanotube (CNT) composite, its conductivity was more than 8 times enhanced to 487 S/m from 59.5 S/m, and the mechanical properties of composites have been improved by more than 15% accordingly. Comparatively, when increased the concentration of CNT or Gr from 1 to 4 wt%, the electrical conductivity of PDMS nanocomposites at 1 mm thickness was barely changed as it generally reached saturation and became independent of filler loading. Compared with the traditional blending method, it indicates that the SCFNA process can further promote the maximum electrical conductivity of polymer nanocomposites when the filler concentration has little effect on the conductivity. Especially under the condition of relatively high filler concentration, the electrical conductivity enhancement effect becomes more significant that is contrary to the classical percolation theory. Moreover, the mechanical properties of the nanocomposites can be slightly improved by the mechanical compression, which makes it more suitable for flexible electronic devices' applications
Solid-State Competitive Destabilization of Caffeine Malonic Acid cocrystal: Mechanistic and Kinetic Investigation
No full textYesThe main objective of this research is to investigate solid-state destabilization mechanism and kinetics of the model cocrystal caffeine : malonic acid (CA:MO) in presence of oxalic acid (OX) as a structural competitor. Competitive destabilization of CA:MO and subsequent formation of CA:OX takes place at temperatures significantly below its melting point. Destabilization mechanism was found to be mediated by sublimation of both CA:MO and OX. During CA:MO destabilization, free CA could not be detected and direct transformation to CA:OX cocrystal was observed. The destabilization kinetics follow Prout-Tompkins nucleation and crystal growth model with activation energy of 133.91 kJ/mol and subsequent CA:OX growth kinetic follow Ginstling – Brounshtien diffusion model with activation energy of kJ/mol
Investigation and design of 5G antennas for future smartphone applications
Get PDFThe fifth-generation (5G) wireless network has received a lot of attention from both
academia and industry with many reported efforts. Multiple-input-multiple-output (MIMO)
is the most promising wireless access technology for next-generation networks to
provide high spectral and energy efficiency. For handheld devices such as smartphones,
2×2 MIMO antennas are currently employed in 4G systems and it is expected to employ
a larger number of elements for 5G mobile terminals.
Placing multiple antennas in the limited space of a smartphone PCB poses a significant
challenge. Therefore, a new design technique using dual-polarized antenna resonators
for 8×8 MIMO configuration is proposed for sub 6 GHz 5G applications. The proposed
MIMO configuration could improve the channel capacity, diversity function, and
multiplexing gain of the smartphone antenna system which makes it suitable for 5G
applications. Different types of new and compact diversity MIMO antennas with Patch,
Slot, and Planar inverted F antenna (PIFA) resonators are studied for different candidate
bands of sub 6 GHz spectrum such as 2.6, 3.6, and 5.8 GHz. Unlike the reported MIMO
antennas, the proposed designs provide full radiation coverage and polarization diversity
with sufficient gain and efficiency values supporting different sides of the mainboard.
Apart from the sub 6 GHz frequencies, 5G devices are also expected to support the
higher bands at the centimeter/millimeter-wave spectrums. Compact antennas can be
employed at different portions of a smartphone board to form linear phased arrays. Here,
we propose new linear phased arrays with compact elements such as Dipole and Quasi Yagi resonators for 5G smartphones. Compared with the recently reported designs, the
proposed phased arrays exhibit satisfactory features such as compact size, wide beam steering, broad bandwidth, end-fire radiation, high gain, and efficiency characteristics.
The proposed 5G antennas can provide single-band, multi-band, and broad-band
characteristics with reduced mutual coupling function. The fundamental characteristics
of the 5G antennas are examined using both simulations and measurements and good
agreement is observed. Furthermore, due to compact size and better placement of
elements, quite good characteristics are observed in the presence of the user and the
smartphone components. These advantages make the proposed antennas highly
suitable for use in 5G smartphone applications.European Union Horizon 2020 Research and Innovation Programme under grant agreement H2020-MSCA-ITN-2016 SECRET-72242
Design of New, Compact and Efficient Microstrip Filters for 5G Wireless Communications
Get PDFThe electromagnetic spectrum is becoming increasingly congested due to the
rapid development of wireless and mobile communication in recent decades.
New, compact and efficient passband filters with multi-functions and good
performance are highly demanded in current and future wireless systems. This
has also driven considerable technological advances in reconfigurable/tunable
filter and filtering antenna designs. In light of this scenario, the objectives of this
thesis are to design, fabricate and measure efficient, compact, multi-standard,
and reconfigurable/tunable microstrip resonator filters and study the integration
of the resonators with patch antennas. As a passive design, a compact dual-band
filter is implemented to cover 2.5 to 2.6 GHz and 3.4 to 3.7 GHz for 4G and 5G,
respectively. Another design is also presented with the advantages of a wide
passband of more than 1 GHz. Conversely, new and compact reconfigurable
filters are designed using varactor and PIN diodes for 4G and 5G. The proposed
filters are tunable in the range from 2.5 to 3.8 GHz. The bandwidth is adjustable
between 40 and 140 MHz with return losses between 17 to 30 dB and insertion
loss of around 1 dB. Also, the thesis investigates the design of cascaded and differentially-fed filtering antenna structures. The cascaded designs operate at
2.4 and 6.5 GHz and have a relatively wide-band bandwidth of more than 1.2
GHz and a fractional bandwidth of more than 40%. For the differentially-fed
structures, good performance is achieved at the 3.5 GHz with a high realized gain
of more than 7.5 dBi is observed.European Union Horizon 2020 Research and Innovation Programme (Marie Skłodowska-Curie Actions) under grant agreement H2020-MSCA-ITN-2016 SECRET-722424
Investigation to Identify the Influence of Mannitol as a Carrier on the Ex-Vivo Dose Emission and the In-Vitro Aerodynamic Dose Emission Characteristics of Dry Powder Inhalers of Budesonide
Get PDFThis study provides, for the first time, an ex vivo comparative evaluation of formulations of budesonide with crystallised β-form mannitol, commercial DPI grade mannitol and lactose. The lactose-budesonide was the marketed Easyhaler® 200 g formulation. Ex vivo assessment of deposition using the Easyhaler® multi-dose high resistance inhaler with reservoir was compared with the RS01® single dose capsule low resistance inhaler at two different inhalation rates. Aerodynamic characteristics, flow and surface energies were investigated together with in vitro and ex vivo assessment of drug deposition. Dose emission was greater for all formulations with higher inhalation flow, indicating greater detachment of drug from carrier, and greater with the Easyhaler®, highlighting the importance of correct device for formulation. Emission was lowest at both inhalation rates for crystallised mannitol due to poor flowability associated with elongated particle shape which resulted in interception deposition. Surface energies were also implicated; closely matched polar surface energy of carrier and drug may be an important inhibiting factor. The promising aerodynamic characteristics of crystallised mannitol with the RS01® inhaler and lactose-budesonide from in vitro assessment were not supported by ex vivo results, highlighting the need for careful selection of device
From Cultural Imperialism to Cultural Peacebuilding. The Role of Media Within the Framework of the Responsibility to Protect Doctrine: The Case of Libya 2011
Get PDFThis thesis undertakes a critical approach to understanding the role of media within the responsibility to protect doctrine framework. The purpose of this work is to respond to the following main two questions: Are there non-violent means that can be applied within the context of the responsibility to protect, Pillar III in particular? Does the conceptualisation of the responsibility to protect and the role assigned to the media prevent or facilitate the application of non-violence to the resolution of humanitarian crises, such as genocide, ethnic cleansing, war crimes and crimes against humanity? In order to investigate the above research questions, it adopts a nuanced Social Constructionist perspective, through which the social function of the media is highlighted. This is achieved through the application of Critical Discourse Analysis, which allowed critical engagement with the semantic position of ‘media’, ‘dialogue,’ and ‘non-violence’ within the founding documents published by the International Commission on Intervention and State Sovereignty and the United Nations that developed the concept of the responsibility to protect between 2001 and 2018. Finally, the work explored how the responsibility to protect has been discussed in selected media outlets that are reflective of two different approaches to journalism, whose underpinning principles differ substantially: mainstream and peace journalism. By adopting the same methodological approach and applying it to the case of the NATO intervention to Libya in 2011 this section of this thesis critically investigated whether there is a difference in their discourse, and, if so, what this difference is
Experimental investigation on the effects of bed slope and tailwater on dam-break flows
No full textYesUnderstanding of the characteristics of dam-break flows moving along a sloping wet bed can help to timely issue flood warning and risk mitigation. In this study, laboratory experiments are carried out in a large flume for a wide range of upstream water depth, bed slopes and tailwater depth. The water level is recorded and processed to calculate the mean velocity and wave celerity. Results show that the increase of the bed slope will significantly accelerate the wave-front celerity for the downstream dry bed, while the negative wave celerity will decrease. When water depth ratio α ≥ 0.3 (defined as the ratio of initial downstream water depth over the upstream water depth of dam), there are extra negative waves propagating towards the reservoir area after the flow has developed for a period of time. When α ≥ 0.6, there are the Favre waves propagating downstream. The water level and the mean velocity fluctuate due to the influence of the extra negative waves and the Favre waves. Such fluctuant frequency increases with the increase of the water depth ratio. The empirical formulas are obtained for the celerity of the first extra negative wave and the first downstream wave. The variation of wave-front height is very similar under three bed slopes investigated in this study, while the maximum wave-front height occurs when α = 0.2. The present study broadens the understanding of the effects of the bed slope and the tailwater level on the movement of the dam-break flows. Furthermore, experimental results are also compared with some analytical solutions. The validity of the assumptions made during the development of these analytical solutions and their limitations are discussed by comparing with the experimental measurements.The National Natural Science Foundation of China (Grant No: 51879179), the Open Fund from the State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University (SKHL1809) and Sichuan Science and Technology Program (No. 2019JDTD0007)
Application of semi-in situ liquid exfoliation of graphite to the scalable production of graphene-epoxy nanocomposites
No full textYesRecent advances in graphite wet exfoliation methods include new solvent systems, exfoliation-assisting agents such as pyrophosphate and use of graphite-intercalated compounds. These open new avenues for the scalable and versatile production of graphene/nanographite composites, with the prospect of reducing barriers to the adoption of these materials for real-world applications. This article proposes a semi-in situ exfoliation method in which graphite is exfoliated directly in the epoxy/cosolvent system via high-shear mixing. The method is tested with three different solvent systems: epoxy/acetone; epoxy/N-Methyl-2-pyrrolidone (NMP); and epoxy/NMP/water. Tailoring of mechanical properties of the composites is achieved by adjusting the mixing and centrifugation times and the temperature of the process. The incorporation of graphite microparticles in the composites has a positive influence on strength and flexibility at the expense of rigidity resulting in a 13.4% increase in ultimate tensile strength (UTS) and 73% in elongation at break (εmax) at 0.04 wt% loading. The proposed method also leads to nanocomposites with enhanced properties at low-filler loadings. For example, the 0.01 wt% loading gave a 7.4% increase in Young's modulus, 10.6% in UTS, and 9.1% in εmax. The scalability and versatility of this method make it a promising alternative for industrial production of epoxy/graphene nanocomposites.School of Applied Sciences, University of Huddersfield, Huddersfield, UK
Pier scour prediction in non-uniform gravel beds
No full textYesPier scour has been extensively studied in laboratory experiments. However, scour depth relationships based on data at the laboratory scale often yield unacceptable results when extended to field conditions. In this study, non-uniform gravel bed laboratory and field datasets with gravel of median size ranging from 2.7 to 14.25 mm were considered to predict the maximum equilibrium scour depth at cylindrical piers. Specifically, a total of 217 datasets were collected: 132 from literature sources and 85 in this study using new experiments at the laboratory scale, which constitute a novel contribution provided by this paper. From the analysis of data, it was observed that Melville and Coleman's equation performs well in the case of laboratory datasets, while it tends to overestimate field measurements. Guo's and Kim et al.'s relationships showed good agreements only for laboratory datasets with finer non-uniform sediments: deviations in predicting the maximum scour depth with non-uniform gravel beds were found to be significantly greater than those for non-uniform sand and fine gravel beds. Consequently, new K-factors for the Melville and Coleman's equation were proposed in this study for non-uniform gravel-bed streams using a curve-fitting method. The results revealed good agreements between observations and predictions, where this might be an attractive advancement in overcoming scale effects. Moreover, a sensitivity analysis was performed to identify the most sensitive K-factors
Descriptors for adamantane and some of its derivatives
Get PDFYesLiterature data on solubilities of adamantane in organic solvents have been used to obtain properties, or descriptors, of adamantane. There is much less data on substituted adamantanes but we have been able to obtain descriptors for some 40 substituted adamantanes. These descriptors can then be used to estimate a wide range of physicochemical, environmental and other properties of the adamantanes. For the first time, the water-solvent partition coefficient and the gas-solvent partition coefficient into a large range of solvents, can be estimated, the latter being equivalent to Henry's Law constants. A variety of other important properties can also be estimated. These include vapor pressures, enthalpies of vaporization and sublimation, partitions from air and from blood into biological tissues, and skin permeability from water. The descriptors themselves are not exceptional. Adamantane itself has a rather low dipolarity, zero hydrogen bond acidity and a very low hydrogen bond basicity, in common with other multicyclic aliphatic compounds. These lead to adamantane being a very hydrophobic compound, as is evident from our estimated water-octanol partition coefficient