32151 research outputs found
Sort by
Observation of Rydberg excitons in nanofabricated Cu₂O crystals and cavities
No full textPhotons, the fundamental particles of light, hold potential for quantum applications. While creating, manipulating, and detecting photons is possible, achieving strong interactions at the single-photon level is challenging. Although photons in a vacuum do not interact, nonlinear interactions with quantum matter can mediate photon-photon interactions, known as single-photon nonlinearity regime. Exciton-polaritons, which are hybrid light-matter quasiparticles, offer a promising path for these interactions. Conventional materials like GaAs struggle to achieve the desired levels of single-photon nonlinearity. Cu₂O Rydberg excitons are promising contenders, due to their giant optical nonlinearities from higher-order Rydberg states that couple strongly with cavity photons. This thesis explores spatial confinement in Cu₂O nanostructured cavities as a viable method to achieve single-photon nonlinearity.
Major results of this work are: (a) Optically tuned Rydberg excitons in Cu₂O pillars fabricated using a focused ion beam, while preserving excitonic properties. We show a size-dependent redshift in excitonic energies which can be harnessed for generating strongly correlated lattices of Rydberg polaritons. (b) Encapsulating Cu₂O nanostructures in microcavities, where a strong coupling of Rydberg excitons (up to n = 8) to cavity photons is first observed by absorption spectroscopy. A thin layer of ITO deposition on the bulk cavity helps in better etching. Photoluminescence of Rydberg excitons (up to n = 5) is observed in the nanostructured and bulk cavities, with an enhancement in the scaling of the nanostructures with reducing dimensions. Understanding the underlying phenomena of the enhancement is key to exploiting the coupling of Cu₂O Rydberg excitons to cavity photons and generating the predicted nonlinearity. The findings pave the way to establish Cu₂O Rydberg polaritons as a scalable platform for photonic quantum simulations."This work was supported by the EPSRC through grant No. EP/S014403/1, by The Royal Society through RGS\R2\192174, by the Leverhulme Trust through grant No. RPG-2022-188, by the ARC Centre of Excellence for Engineered Quantum Systems (CE170100009). I acknowledge the support of the EPSRC Capital for Great Technologies Grant EP/L017008/1 and the EPSRC Strategic Equipment Resource Grant EP/R023751/1 for the use of FIB equipment for the fabrication of nanostructures."--Fundin
Homochiral carboxylate-anchored truxene tripods : design, synthesis, and monolayer formation on Ag(111)
Get PDFFunding: This work was supported by JSPS KAKENHI Grants-in-Aid for Scientific Research (A) (JP24H00484) and (B) (JP20H02784, JP23H02013), and Scientific Research on Innovative Areas “Aquatic Functional Materials” (JP22H04541), “Molecular Engine” (JP21H00400) and “Coordination Asymmetry” (JP19H04567), a Grant-in-Aid for Transformative Research Areas (A) “Dynamic Exciton” (JP20H05836), and “Supra Ceramics” (JP23H04626), Japan Science and Technology Agency (JST) PRESTO (JPMJPR21 A2) and JST CREST (JPMJCR2302) from MEXT. This work was also supported by the Yazaki Memorial Foundation for Science and Technology, Iketani Science and Technology Foundation (ISTF), the Foundation for the Promotion of Ion Engineering, Kansai Research Foundation for Technology Promotion, and the Research Program of “Five-Star Alliance” in “NJRC Mater. & Dev.”. We thank Prof. Masahiro Miura (Osaka University) for the CPL measurements. Financial support of K.M. by EPSRC (EP/T518062/1 & EP/R513337/1) and the School of Chemistry, St Andrews University, is gratefully acknowledged. M.Z. thanks the Helmholtz Zentrum Berlin (HZB) for the allocation of synchrotron radiation beamtime at BESSY II and financial support as well as Dr. M. Brzhezinskaya (HZB) for the assistance during the measurements at BESSY II. Open Access funding enabled and organized by Projekt DEAL.The design of well-defined assemblies of chiral molecules is a prerequisite for numerous applications, such as chirality-induced spin selectivity (CISS). In this context, tripodal molecular films bear the advantage of better control of molecular orientation and alignment than analogous monopodal systems. To this end, we report on the synthesis and assembly property of C3 chiral syn-5,10,15-truxene triacetic acid. (S,S,S) and (R,R,R) enantiomers were isolated and adsorbed on underpotential deposited Ag(111)/Au/mica both individually and as a racemate. The enantiomers form a densely packed and well-ordered structure (including the azimuthal alignment), even though with small sizes of individual domains. The molecules adsorb predominantly in tripodal configuration, with all three docking groups bound to the substrate as carboxylates in a bidentate fashion. The truxene backbone is then oriented parallel to the substrate surface but the fluorene blades are twisted to some extent. The racemate monolayer turned out to be less densely packed and less well-ordered compared to the films of individual enantiomers, which underlines the fact that uniform chirality is primarily important for molecular ordering of the truxenes. We hope that the designed system will be useful in the context of CISS and stimulate further activities regarding chiral tripods.Peer reviewe
Dominance relations of Norway rats in pairs versus in groups
No full textFunding: For this work, funding was provided to MAP-E (Scholarship Program 783-2017 of the Ministry of Science, Technology, and Innovation—Minciencias, formerly Colciencias) and CKH (Lucie Burgers Foundation grant) for the research project titled ‘Sex and competitive dynamics in groups of rats: is there resemblance to primates?’.Several experimental studies assessing the hierarchy of a group in nonhuman animals have tested pairs of subjects in isolation. However, mounting evidence suggests that the dominance hierarchy of individuals tested in groups differs from that of individuals tested in pairs. In the present study, we compared the hierarchy of the same wild-type Norway rats, Rattus norvegicus, when tested in groups in the so-called Visible Burrow System, and pairs in the classic dyadic tube test. We show that the dominance order derived in groups differed from that inferred in pairs and was less stable in groups. This difference may be due to the presence of bystanders when testing in groups and their absence in isolated pairs. This suggests that the dominance hierarchy in a group is not reliably inferred when testing isolated pairs, and the classic tube test should be reconsidered as a standard protocol for dominance assessments in rats.Peer reviewe
DNA sensing with whispering gallery mode microlasers
Get PDFFunding: Alexander von Humboldt-Stiftung.Nucleic acid sensing is crucial for advancing diagnostics, therapeutic monitoring, and molecular biology research by enabling the precise identification of DNA and RNA interactions. Here, we present an innovative sensing platform based on DNA-functionalized whispering gallery mode (WGM) microlasers. By correlating spectral shifts in laser emission to changes in the refractive index, we demonstrate real-time detection of DNA hybridization and structural changes. The addition of gold nanoparticles to the DNA strands significantly enhances sensitivity, and exclusively labeling the sensing strand or a hairpin strand eliminates the need for secondary labeling of the target strand. We further show that ionic strength influences DNA compactness, and we introduce a hairpin-based system as a dual-purpose sensor and controlled release mechanism for drug delivery. This versatile WGM-based platform offers promise for sequence-specific nucleic acid sensing, multiplexed detection, and in vivo applications in diagnostics and cellular research.Peer reviewe
Glacial lake mapping and monitoring using SAR and optical satellite data : development and applications of algorithms
No full textGlaciers around the world are retreating and thinning due to atmospheric warming resulting in the formation and expansion of glacial lakes. Glacial lakes can affect glacier mass balance and glacier dynamics. They are also a source of catastrophic glacial lake outburst floods (GLOFs). Remote sensing-based mapping and monitoring of glacial lakes are crucial for people living in the nearby glacierized catchments for the early detection of GLOFs with minimal costs. Although many remote sensing techniques already exist for mapping glacial lakes, the generic challenges of approaches include cloud cover, frozen glacial lake surface, turbidity, and shadows from mountains and clouds. Moreover, the remote sensing-based monitoring routines are of low frequency and mainly rely on optical remote sensing data. In this thesis, I have used multi-source remote sensing data from sensors such as Landsat, Sentinel-1 Synthetic Aperture Radar (S-1 SAR), Sentinel-2 Multispectral Instrument (S-2 MSI), and digital elevation models (DEMs) to develop, test, and validate glacial lake mapping and monitoring algorithms that address aforementioned challenges. When necessary, I have also used field photographs and high-resolution remote sensing data to validate results. I mainly focused on the Bhutanese Himalayas, and the alpine regions were also considered. The main approaches I used include threshold-based image segmentation, rule-based image segmentation, the Normalised Difference Water Indices (NDWIs), Persistent Scatterer Interferometry (PSI), and machine learning techniques (e.g., random forest).
Using S-1 SAR data, a semi-automated method for lake mapping based on a radar backscatter intensity threshold was presented for the Bhutanese Himalayas. The lake mapping results were accurate. However, the overall accuracy was low due to false positives requiring multiple post-processing steps to improve the accuracy. The main advantage of using S-1 SAR for lake mapping was the high temporal frequency of data acquisition and no cloud cover allowing repeated mapping of glacial lakes. Another glacial lake mapping method was proposed using S-1 SAR data, S-2 MSI data, rule-based image segmentation, and random forest classifier algorithm. The method was tested and validated in eight test sites across the alpine regions. It integrated the strengths of multi-source data and multiple techniques to map glacial lakes. The overall accuracy of the method was greater than 95% in all the test sites.
The time series S-1 SAR data, Google Earth Engine (GEE), and PSI technique were used to develop a method for monitoring glacial lakes at high frequency (every six days) in the Bhutanese Himalayas. The method was validated against the field photographs taken in 2016 and DEM differencing results generated using SPOT-7 and Pleiades data. The integrated use of GEE and time series S-1 SAR data improved hazard assessment techniques by quantifying glacier and basin melt areas, glacier and lake freeze-thaw cycle, and lake area and open water area changes. The PSI results revealed information about the stability of surrounding slopes and moraines of glacial lakes. Using the proposed approaches, an objective and systemic near-real-time mapping and monitoring of glacial lakes across alpine regions should be possible with certainty where field investigation is challenging due to rugged topography, geopolitics, and limited financial resources. Integrating knowledge, methods, tools, and techniques into the early warning systems by decision-makers and scientists is recommended
The Turkic inscription at the Imam Ali shrine in Najaf
Get PDFThis article introduces the 18th-century ʿAjemī/Qizilbāsh Turkish inscrip-tion at the Imam ʿAlī shrine to the English-speaking academic world. The poetic inscription was commissioned in 1743 by Nādir Shāh during his invasion of Ottoman Iraq, where he sought to compel the Porte to recognize his Jaʿfarī creed (maẕhab) as a legitimate school of Sunnī jurisprudence, ostensibly in the interests of Islamic unity. It is argued that the inscription formed part of Nādir’s discourse on establishing Islamic unity as a world sovereign. The inscription drew from various pre-Islamic sources of legitimacy to articulate Nādir’s mandate for universal sovereignty. It then fused this mandate with a distinctly ʿAlīd conception of universal caliphal authority that could appeal to both his Jaʿfarī and Ḥanafī followers. Thus, by analyzing the text of the inscription within the political and socioreligious context in which it was created, new insights are offered on the purpose of the inscription, the role it played in Ottoman–Iranian peace negotiations, and Nādirid political and religious legitimacy. Finally, a complete translation and a transcription are appended herein.Peer reviewe
Themes in von Herbert's letters to Kant : deception, happiness and meaning
Get PDFIn the late eighteenth century, a young Austrian woman named Maria von Herbert, member of a philosophical circle in Klagenfurt at the house of her and her brother, corresponded with Immanuel Kant. She wrote a total of three letters to Kant, of which the last two remained unanswered. The aim of this thesis is to show that their correspondence not only sheds light on contentious topics in Kant's philosophy, but that von Herbert’s letters constitute an early critique of Kant's moral philosophy. First, I investigate the way reticence, candour and deception relate in light of Kant’s letter to von Herbert and argue that deception is not always morally wrong for Kant, and that von Herbert’s "prolonged lie" is not a vice. Second, I explore the concept of happiness and assess von Herbert’s argument that virtuous people are more likely to be unhappy. Third, I discuss the theme of meaning. I argue that von Herbert found herself in a state of profound boredom, involving a loss of meaning, and that it was her primary reason for writing to Kant. I investigate several avenues to see whether Kant's philosophy can account for the significance of meaning and conclude that ultimately it cannot account for meaning in a satisfactory way. Finally, I construe von Herbert's critique as pointing out that of the three components of "the good life" – morality, happiness and meaning – Kant’s moral agents only have room to strive for morality and suggest that this is ultimately a failing of Kant's philosophy
Synchrotron-source micro-x-ray computed tomography for examining butterfly eyes
Get PDFFunding: This project was funded through the National Science Foundation NeuroNex Innovation Award # 1707405 and The Pritzker Fellowship, awarded to rising second-year neuroscience students who have shown the most promise based on their outstanding academic performance during their first year in graduate school.Comparative anatomy is an important tool for investigating evolutionary relationships among species, but the lack of scalable imaging tools and stains for rapidly mapping the microscale anatomies of related species poses a major impediment to using comparative anatomy approaches for identifying evolutionary adaptations. We describe a method using synchrotron source micro-x-ray computed tomography (syn-μXCT) combined with machine learning algorithms for high-throughput imaging of Lepidoptera (i.e., butterfly and moth) eyes. Our pipeline allows for imaging at rates of ~15 min/mm3 at 600 nm3 resolution. Image contrast is generated using standard electron microscopy labeling approaches (e.g., osmium tetroxide) that unbiasedly labels all cellular membranes in a species-independent manner thus removing any barrier to imaging any species of interest. To demonstrate the power of the method, we analyzed the 3D morphologies of butterfly crystalline cones, a part of the visual system associated with acuity and sensitivity and found significant variation within six butterfly individuals. Despite this variation, a classic measure of optimization, the ratio of interommatidial angle to resolving power of ommatidia, largely agrees with early work on eye geometry across species. We show that this method can successfully be used to determine compound eye organization and crystalline cone morphology. Our novel pipeline provides for fast, scalable visualization and analysis of eye anatomies that can be applied to any arthropod species, enabling new questions about evolutionary adaptations of compound eyes and beyond.Peer reviewe
The shocking stars : numerical modelling of stellar feedback in giant molecular clouds
Get PDFFrom the scales of molecular clouds to galaxies, feedback from massive stars is crucial for understanding the star formation process. Type II supernovae are deemed one of the biggest source of energy and momentum in the interstellar medium. They limit the cold gas reservoir by dispersing clouds and launching galactic outflows. Meanwhile, pre-supernova feedback, such as ionizing radiation, may modify the environment of supernova progenitors by creating bubbles and channels. These structures largely determine the dynamical impact of feedback.
The first half of this thesis describes the numerical methods I used for studying photoionization in star-forming regions. We employed the smoothed particle hydrodynamics (SPH) technique to simulate the molecular clouds. I present our tree-based radiation hydrodynamics scheme that couples SPH to Monte Carlo radiative transfer code for modelling H ɪɪ regions. This scheme also involves novel algorithms for setting up pseudo-SPH particles, and for computing photoionization heating and cooling.
The second half of the thesis investigates how feedback energy leaves the cloud preferentially through the paths of least resistance, and what it implies about our current supernova sub-grid models. I devised an analytical model to describe supernovae that are partially confined in a porous feedback-driven cavity. The analytical model is verified with simulations of idealized clouds with simplified geometries, and with turbulent molecular clouds in realistic environments. I compared them against supernova blasts in homogeneous environments which are often used to formulate the 1-D feedback prescriptions. I showed that semi-confined supernovae can sustain a relatively higher kinematic input in regions closer to the progenitor, and I argue for the importance of incorporating channelling effects into feedback models
Novel zeotype frameworks for catalytic applications : design, synthesis and characterisation
Get PDFA combination of experimental synthetic and structural studies, performed in the light of modelling, has been used to design and prepare novel microporous silicoaluminophosphate (SAPO) zeotypes of potential application as catalysts.
Cu²⁺ and Ni²⁺ cations complexed by linear polyamines have been studied as structure- directing agents (SDAs) for the direct synthesis of copper- and nickel-containing microporous silicoaluminophosphate (SAPO) materials. The complexing ligands diethylenetriamine (DETA), N-(2-hydroxyethyl)ethylenediamine (HEEDA), triethylenetetramine (TETA), N,N′-bis(2-aminoethyl)-1,3-propanediamine (232), 1,2- bis(3-aminopropylamino)ethane (323), tetraethylenepentamine (TEPA) and pentaethylenehexamine (PEHA) have been investigated. Cu and Ni forms of both SAPO-18 and SAPO-34 materials have been prepared. While most Cu and Ni polyamine complexes direct crystallisation to SAPO-34, SAPO-18 has been prepared with Cu²⁺ 232 and Ni²⁺ complexes of 232 and TETA. The coordination geometry of the included metal complexes was studied by UV-visible and EPR spectroscopy and computer simulation. SAPO-18 is favoured by the smaller square planar complexes or octahedral species (with 2 water molecules) of 232 and TETA. Rietveld analysis has allowed to locate extra-framework Cu²⁺ and Ni²⁺ cations released by calcination. In SAPO-34, Cu²⁺ and Ni²⁺ were located within the cha cage within the 8R window. A second site was found for Ni²⁺ at the centre of the six-membered rings (6Rs) of the double-six-ring (D6R) sub- units. In SAPO-18 both Cu²⁺ and Ni²⁺ cations were located only in the 6Rs of the D6R sub-units. Selected copper SAPO-18 and SAPO-34 samples were tested in the selective catalytic reduction of NO with ammonia (NH₃-SCR): both showed high activity.
SAPO-34-containing Fe cations in extra-framework position has been prepared by the one-pot approach for the first time using DETA, TETA, TEPA and PEHA as SDAs. The coordination sphere and oxidation state of the Fe cations within the as-prepared and calcined SAPO-34 materials specifically those prepared with Fe-TEPA, were investigated by combining UV-visible and Mössbauer spectroscopies. Iron cations were found to be in two different octahedral coordinations within the as-prepared hydrated
SAPO-34: assigned as [Fe(TEPA)(H2O)]²⁺ and [Fe(TEPA)(O2)]²⁺, respectively. Furthermore the Fe²⁺-TEPA complex contained within SAPO-34 was found to have interesting properties as a reversible O2 carrier. The calcined sample contains octahedral isolated or dimeric Fe³⁺ species well dispersed within the SAPO-34 pores. In order to prove the novelty of our material, Fe-SAPO-34 was synthesised as described in a U.S. Patent Application 2012/0251422. Freshly calcined, one-pot synthesised, Fe- SAPO-34 material shows a greater activity for the SCR DeNOx process than that shown by the US patent sample.
A retro-synthetic method to design the synthesis of target silicoaluminophosphates whose framework belongs to the ABC-6 structural family and has at least one gme cage per unit cell has been successfully developed. This strategy allowed the preparation of SAPO versions of AFX (SAPO-56), SFW (STA-18) and GME (STA-19) types of framework. To the best of my knowledge, the last two SAPOs have been prepared for the first time. The method is based on the use of two SDAs simultaneously, to promote the formation of structure features such as cages or channels of the target framework type. Computational modelling was employed to locate energetic favourable quaternary ammonium compounds and diquaternary salts of diazabicyclooctane (DABCO) with optimal shape and size to template the gme cage and the secondary cages or channels of the target structures, respectively. Trimethylammonium cations showed the most favourable energies for the gme cage while bisDABCO salts and quaternary ammonium oligomers of DABCO with connecting polymethylene chain lengths between 4 and 8 methylene units showed a good fit for the secondary cages or channels. The incorporation and location of the SDAs were determined combining ¹³C MAS NMR, CHN, TGA, computational modelling and Rietveld refinement on PXRD data.
Trimethylamine and diDABCO-C6 have been found to template the crystallisation of a new microporous silicoaluminophosphate framework structure, denoted STA-20 (St. Andrews microporous material-20). The structure of SAPO STA-20 was determined by combining powder diffraction, electron crystallography, and computer modelling
(P-31c, a = b = 13.15935(26) Å, c = 30.5837(6) Å). STA-20 is a unique member of the ABC-6 family of which the stacking sequence, AABAABAACAAC(A), is the equal longest stacking sequence in the subfamily of ABC-6 structures consisting of 6Rs and D6Rs, on a par with the SAT structure. Moreover STA-20 contains the longest cavity observed in ordered ABC-6 materials. The location of the templates within the framework was determined by combining computer modelling and Rietveld refinement against X-ray data. MAS NMR and N₂ adsorption have also been used to further characterise the solid.
Two new disordered silicoaluminophosphate structures belonging to the ABC-6 family were obtained by the combination of specific SDAs. GME-CHA and babelite-AFX intergrowth structures, generically named SAPO STA-22, were prepared by combining trimethylamine, cyclam and ferrous acetate in a SAPO preparation. An intergrowth AFX-CHA structure, denoted SAPO STA-23, was synthesised by partially replacing diDABCO-C4 with Cu- or Fe-TEPA in the preparation of SAPO-56 employing the ‘double- template’ method mentioned above giving a transition-metal containing SAPO-56 by the one-pot approach. The selected-area electron diffraction (SAED) patterns and the simulations of the experimental PXRD pattern performed employing the computer program DIFFaX have allowed us to determine the types of stacking in the materials, which solid-state UV-visible spectroscopy, MAS NMR and N2 adsorption have been used to further characterise them
Access Repository Dashboard
Do you manage St Andrews Research Repository? Access insider analytics, issue reports and manage access to outputs from your repository in the CORE Repository Dashboard!