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Ultracold and quantum degenerate mixtures of Cs and Yb
Get PDFThe study of ultracold mixtures of neutral atoms builds on the techniques of trapping and cooling single species of atoms to access more complex physical systems, and provides a route towards formation of ultracold molecules. In this thesis, we experimentally produce and study ultracold mixtures of Cs and Yb. This choice of Cs and Yb gives a versatile experimental system, with high tuneability of reduced mass, intraspecies and interspecies scattering properties, and the ability to study Bose-Bose and Bose-Fermi atomic mixtures. A long-term goal of working with the mixture is production of ultracold CsYb molecules. The CsYb molecule has a 2-Sigma symmetry ground state, and both magnetic and electric dipole moments. An array of such CsYb molecules would therefore be a versatile experimental platform for applications such as quantum simulation of physical systems, quantum computation and ultracold quantum chemistry.
In this thesis, we report on experimental observations within the Cs-Yb mixture, made possible by the implementation of a bichromatic optical dipole trap consisting of individual dipole trapping beams of 532 nm and 1070 nm. This trap has been designed to overcome the problems of mismatched trap depths and in-trap losses previously encountered in a single-wavelength optical dipole trap. This allowed us for the first time to produce dual quantum degenerate mixtures. We report production of pure dual Bose-Einstein condensates (BECs) of Cs+174Yb with N_Cs~5x10^3 and N_Yb~7x10^4. We also report production of pure dual BECs of Cs+170Yb with N_Cs~1x10^4 and N_Yb~4x10^4. We further study these quantum degenerate mixtures, observing their lifetimes, dynamics, and properties such as mixture immiscibility and dual-species collapse.
We further improve the versatility of our experimental apparatus by implementing an optical lattice with tuneable wavelength. The lattice can operate at two Cs `tune-out' wavelengths in the region of 460 nm. This allows a species-specific lattice potential which traps only Yb. Alternatively, it can be operated at wavelengths where either the trapping potential or the trap frequency is balanced for Cs and Yb. We measure the polarizability of Cs with Kapitza-Dirac diffraction of a Cs BEC using the tuneable lattice. This helps us obtain a more precise measurement of the Cs tune-out wavelengths.
Finally, we investigate a potential route to formation of CsYb molecules by performing Feshbach spectroscopy on an ultracold mixture of Cs+173Yb. Using predictions supported by previous experimental and theoretical work, we report the first experimental observations of interspecies magnetic Cs-Yb Feshbach resonances. We observe two sets of resonances, at magnetic bias fields around 622 G and 702 G. These observations motivate further discussion on the utilisation of the resonances for magnetoassociation, as well as experimental techniques to detect and manipulate the nuclear spin substate composition of Fermionic Yb
An empirical analysis of Total Factor Productivity (TFP) in Mexico, 1993-2018: determinants, decomposition and convergence
Get PDFThis research estimates TFP at the establishment level in Mexico at 5-year intervals from 1993 to 2018. The production function used to estimate TFP includes a mark-up correction to overcome the omitted price bias, and the Wooldridge (2009) approach overcomes the endogeneity bias. The TFP analysis is divided into three categories: determinants, decomposition and convergence. The first category of the research identified six TFP determinants at the establishment level. The main findings are: (i) firm age positively impacts TFP, indicating a learning-by-doing effect; (ii) managerial and organisational efforts to reduce costs increase TFP; (iii) higher industrial concentration positively impacts TFP, suggesting that higher competition does not necessarily lead to higher TFP (i.e. Schumpeterian models); (iv) MAR externalities positively impact TFP due to localised economies of scale; (v) Jacobian externalities negatively affect TFP as a result of potential urbanisation costs; (vi) population density negatively affects TFP due to potential congestion costs in most sectors. The second category of the research analysed TFP decomposition by geographical locations, economic sectors and the contribution of firm selection to TFP growth. The geographical dimension of TFP indicates three clusters of states with high TFP: (i) some states in the North of Mexico, with potential productivity spillovers due to proximity with the U.S; (ii) states with high agglomeration economies, including Mexico City, Jalisco and contiguous states; and (iii) states in the Southeast, including Campeche and Tabasco, which are states mainly dedicated to oil extraction (i.e., natural advantages). The sectoral dimension of TFP accounts can be classified in three sectors with high TFP: (i) mining, quarrying, and oil and gas extraction, (ii) wholesale and retail trade, (iii) finance and insurance. Overall, services and oil extraction had a high TFP during 2018 while manufacturing activities had a low TFP performance. The Mexican economy had a negligible TFP growth of 0.10% from 1998 to 2018, and there was calculated the TFP growth decomposition regarding the contribution of surviving, entering and exiting establishments. The TFP growth decomposition shows a positive contribution of net entrants but a negative contribution of survivors. The condition of survival has deteriorated its contribution to TFP growth since the financial crisis (2008-2009). Conversely, business creation has been a driver of TFP growth. The third category of the research analysed TFP convergence across Mexican states and municipalities. There is no evidence of TFP convergence across states due to a potential aggregation bias. However, there is evidence of TFP convergence at the municipality level, which is associated with a reduction of TFP disparities across municipalities. Mexican municipalities had an absolute convergence rate of 0.21% per annum (1998-2018), and it would take around 323 years to eliminate 50% of the TFP gap across municipalities (i.e. half-life period). This thesis concludes with recommendations for an industrial strategy to increase TFP in Mexico
Magma Chemical Evolution in the Lesser Antilles Arc Crust: Insights from Plutonic Xenoliths
Get PDFMagmas generated beneath volcanic arcs at subduction zones must traverse the crust
of the overriding plate, via “magma plumbing systems” prior to eruption. Magma
plumbing systems are predominantly composed of crystal mush, where low volumes
of melt are distributed throughout higher volumes of crystals. To understand processes
controlling the chemical compositions of arc lavas, it is essential to constrain how
magmas are chemically modified within mushy plumbing systems during storage and
transit through the upper plate crust. Arc lavas often carry fragments of crystal mush,
known as plutonic xenoliths, to the surface, which can be used to study the influence
of crustal processes on arc magma chemical compositions.
This thesis investigates plutonic xenoliths from the islands of Martinique and St
Vincent in the active intra-oceanic Lesser Antilles arc. These samples are used to
determine whether the majority of the trace element and isotopic variation in Lesser
Antilles arc lavas can be produced by crustal processes. Strontium isotopic
compositions of plagioclase, in plutonic xenoliths derived from different crustal
depths, are used to demonstrate that isotopic variation and highly radiogenic isotopic
compositions observed in Martinique lavas are acquired via assimilation of upper
crustal sediments. Textural features and mineral trace element compositions in St
Vincent plutonic xenoliths record polybaric fractional crystallization and melt-mush
reaction processes. These two processes control magma chemical evolution in mushes
beneath the island and consequently influence the trace element compositions of St
Vincent lavas.
These findings suggest that majority of trace element and radiogenic isotopic variation
in Lesser Antilles arc lavas is generated within mushy magma plumbing systems in the
arc crust. An important wider implication is that contributions from crustal processes
must be well constrained before using trace element and isotopic compositions of arc
lavas to assess subduction recycling processes and mantle source heterogeneity
The Complexity of Some Geometric Proof Systems
Get PDFIn this Thesis we investigate proof systems based on Integer Linear Programming. These methods inspect the solution space of an unsatisfiable propositional formula and prove that this space contains no integral points.
We begin by proving some size and depth lower bounds for a recent proof system, Stabbing Planes, and along the way introduce some novel methods for doing so.
We then turn to the complexity of propositional contradictions generated uniformly from first order sentences, in Stabbing Planes and Sum-Of-Squares.
We finish by investigating the complexity-theoretic impact of the choice of method of generating these propositional contradictions in Sherali-Adams
Atom-light interaction in nano-structured alkali-metal vapour cells
Get PDFWe present an experimental and theoretical study into the behaviour of thermal atoms confined to bespoke micro- and nano-structured vapour cells. We detail advancements to our cell platform, and use our cells to study a number of physical effects at novel lengthscales. We study light-induced atomic desorption (LIAD) for localised liberation of wall-adsorbed atoms into the vapour phase, and demonstrate density increases of up to 5× in a micron-scale region. We also find that non-resonant laser light can create high density condensed regions of rubidium on the cell walls. We demonstrate two-colour excitation and fluorescence spectroscopy in a nano-cell, and use this scheme to measure the density distribution of atoms confined to a 1 × 1 µm channel. We measure an exponential decay with distance into the channel, with a lengthscale of 4.0(11) µm. Finally, we study the response of confined vapours to resonant nanosecond laser pulses. We measure the decay time of the fluorescence activity from single-colour excitation to the 5P3/2 to be much less than the natural lifetime, which we conclude to be due to atomic time of flight. We also perform pulsed excitation to the 5D5/2 state using a two-colour scheme in various geometries, and produce a Monte Carlo wavefunction simulation to model this. We conclude that, in this case involving the longer lived 5D5/2 state, velocity selectivity and time of flight both impact the measured timescale, and use our simulations to extract the contributing velocity classes. Due to the selectivity imposed by our cells, we measure a decay timescale of 38.71(13) ns in a 1 µm cell, despite the mean atomic time of flight being only approx. 3 ns. We discuss the implications of our results in the context of both fundamental physics and technological applications throughout
Understanding complex phenomena in colour and development of a novel laundry metric
Get PDFDiffuse reflectance spectroscopy (DRS) is a powerful non-contact technique for probing the physical world. In this project it was applied to two main areas of study, colourimetry and chemometrics. Chapter 1 gives a review of the relevant concepts used throughout this study. Chapter 2 first explores the origin of the difference in perceived colour when compounds containing certain lanthanide ions are viewed under sunlight or fluorescent lighting. It was found that salts of neodymium and holmium are subject the the largest change in colour. The cause of this phenomenon was found to be the overlap of the concentrated green component in fluorescent lighting with absorption bands of the lanthanide ions, leading to illuminant metamerism. The phenomenon observed in neodymium chloride was then utilised in order to control the perceived appearance of a sample to any hue using a custom-build spectrally tunable light source, while maintaining near-white illumination. The process was herein termed tunable illuminant metamerism.
The colourimetry models which could accurately describe the complex colour appearance of lanthanide salts were then applied to study the workings of fluorescent whitening agents (FWAs) and hueing dyes (HDs) on the colour correction of naturally degraded fabric (yellowing). A platform was developed which could be used to model the appearance fabric under different lighting conditions, at different stages of yellowing while simulating the effects of FWAs and HDs.
In chapter 3, DRS is applied to study the lipid component of laundry stains, and a technique for the quantification of lipid on fabric substrates by short-wave infrared DRS was devised. A unit system for comparing the concentration of lipid on fabric, termed wt%, was first discussed and calibration samples of uniformly set lipid concentration were prepared and measured using DRS to yield a dataset for machine learning. A combination of preprocessing techniques, principal components regression and Gaussian process regression models were used to model lipid concentration from DRS spectra. The validity of the best performing model was tested on an external sample set with consistent results, confirming that the proposed technique is capable of non-contact quantitative measurements of lipid concentration on fabric. The approach was applied to point-scan imaging where the concentration of lipid across a fabric could be quantitatively mapped and results were verified by gravimetry. Further validation of the developed machine learning models is still required as the method of producing calibration samples of low lipid concentration was found inaccurate at low levels of staining. A revised method for producing uniform calibration samples using inkjet printing was investigated to address this issue and found to be feasible
Identification of olfactory cues for egg laying in the Black Soldier Fly, an industrially important insect species
No full textUltrafast dynamics at aqueous-air interfaces
Get PDFA femtosecond time-resolved surface electronic sum-frequency generation spectroscopy setup has been constructed in conjunction with a femtosecond transient absorption setup. The layouts are described, along with the principles of their use. In the case of the surface experiment, a novel combination of existing techniques has enabled nonlinear spectroscopic measurements to be performed on fluorescent samples by optical Kerr gating of the surface nonlinear response. The sum-frequency generation and transient absorption setups were used together to investigate the hydrated electron formed by photo-oxidation of the phenolate anion at the aqueous/air interface and in solution. The hydrated electron is important across a breadth of chemistry, and is relevant to areas such as atmospheric, nuclear, and biological chemistry, where it is considered an important species in reductive DNA damage. The surface electron was observed to exhibit similar dynamics to the same bulk system, albeit at an accelerated rate. The study was improved by observing dynamics across a range of wavelengths, which showed a variation in dynamics across the spectral regions probed. The variations in dynamics were attributed to a second species at the interface: the phenoxyl radical. Kinetics and associated spectra of both species were retrieved from the data, exhibiting the first optical spectrum of the hydrated electron at the aqueous/air interface. Finally, potential chemical systems and experimental developments of interest are presented
The misfit of music in a higher education government institute for Emirati women: An ethnographic study exploring the pursuit of music as an activity in a conventional Islamic setting.
Get PDFPeople appear to have a natural disposition toward music. Although music’s presence is evident in all cultures, for many Muslims it not only lacks value as an activity, it is perceived to be incompatible with Islamic principles. This study investigates the complexity involved in navigating the clash of perceptions when engaging in music as an activity, especially within the United Arab Emirates (UAE) as a traditional Muslim country.
The thesis examines a music club activity facilitated by the researcher, a non-Muslim instructor of English who is untrained in teaching music but has years of experience running extracurricular music activities. The club takes place in the women’s campus of a government higher education institution for UAE nationals and explores the music involvement of nine participants. Two of the participants were Western staff members - one male, one female - and the rest were Emirati female students.
This ethnographic study used semi-structured interviews and participant observations to explore the club members’ involvement with the activity over the space of an academic year. Of interest to this investigation were three aspects: first, the perceptions participants encountered towards music within the Muslim community; second, the factors contributing towards participants’ involvement in music activity even though they acknowledged its disapproval among Muslims and third, the experience club members encountered engaging in music as a collaborative pursuit.
Activity theory (AT), also known as cultural historical activity theory (CHAT), recognises the multifaceted nature of human action. It provided the analytical lens that could incorporate the complexities and challenges of a music activity in an Emirati context. However, AT has been criticised for giving greater focus to the culture and history associated with the activity itself and overlooking the cultural and historical factors impacting participants’ contribution to an activity. With its focus on the experience of club members collaborating to achieve the activity object of producing music, this study aims to add to activity theory as an area of knowledge. Most importantly given the polemical viewpoints held toward music and until recently its lack of presence for students aged over 13 years, there is a dearth of research in the area of music in the Emirati education system. This study will contribute to this under-represented field of academic knowledge
A Novel Strategy for Longer Term Differentiation of Human Embryonic Tissues from Pluripotent Stem Cells and Simulations of Teratoma Formation In Vitro
No full textUnderstanding the mechanisms that occur during human tissue development is a major challenge in the fields of developmental biology, stem cell biology and regenerative medicine. Currently, various methods have been employed to study this process; however, each of them has its unique advantages and limitations. Working with human embryos represents a more physiologically option; nevertheless, ethical concerns arise due to its nature. Animal models
are a popular method to elucidate signalling pathways and processes. However, animal studies are not always representative of human events. In vitro models employing human pluripotent stem cells have become an important surrogate for studying human embryogenesis and tissue differentiation. Nevertheless, these cell culture systems do not always provide the appropriate microenvironmental cues in a spatiotemporal manner to enable hPSCs to differentiate into complex 3D tissue structures. Having a better understanding of this topic will allow for the development of more robust differentiation protocols, the creation of cell therapies to treat diseases, and the study and characterisation of human pluripotent stem cells.
In this project, a two-step culture method which combines hPSC-derived embryoid bodies (EBs) with porous scaffold was established to enhance their viability and extend their
differentiation. This approach enabled the formation of tissue-like structures of increasing complexity over time. Furthermore, manipulating their differentiation through physical and chemical cues towards specific germ layers was possible and successful. The introduction of co-culture and dynamic systems impacted importantly the differentiation and morphology of the tissue structures formed. Human EB derived tissues were highly reminiscent of xenograft teratoma samples from the same human pluripotent stem cell population. This confirms the similarity and complexity of the in vitro tissue-like structures to the in vivo samples.
The novel in vitro model developed in this study offers a controllable and reproducible method to form complex tissue structures in vitro for studying human tissue development, as well an animal-free alternative to the teratoma assay
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