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192 results on '"MacDonald, Kevin"'

21. Role of asymmetries in q-BIC formation

Author

MacDonald, Kevin F., Staude, Isabelle, Zayats, Anatoly V., Weigand, H., Millet, L., Carletti, L., de Ceglia, D., Rocco, D., Saerens, G., Gao, J., Barati Sedeh, H., Li, W., Litchinitser, N. M., Grange, R., and Vincenti, M. A.

Published
2024
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22. The prehistory of Jebel Moya, Sudan: results from the first three seasons of excavations.

Author

Vella Gregory, Isabelle, Brass, Michael, Adam, Ahmed, Kozieradzka-Ogunmakin, Iwona, MacDonald, Kevin, Abdelwahabe, Shadia, Fedlelmula, Abdelhai, Hajjaj, Ezzeldin, Fuller, Dorian Q, den Hollander, Anna, Khalid, Musaab, Ali, Omer Elsir, Ibrahim, Marsa Hashim, and Ibrahim, Hanaa

Abstract

Copyright of Libyan Studies is the property of Cambridge University Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Published
2023
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23. Picophotonic localization metrology beyond thermal fluctuations

Author

Liu, Tongjun, Chi, Cheng-Hung, Ou, Jun-Yu, Xu, Jie, Chan, Eng Aik, MacDonald, Kevin F., and Zheludev, Nikolay I.

Abstract

Despite recent tremendous progress in optical imaging and metrology1–6, there remains a substantial resolution gap between atomic-scale transmission electron microscopy and optical techniques. Is optical imaging and metrology of nanostructures exhibiting Brownian motion possible with such resolution, beyond thermal fluctuations? Here we report on an experiment in which the average position of a nanowire with a thermal oscillation amplitude of ∼150 pm is resolved in single-shot measurements with subatomic precision of 92 pm, using light at a wavelength of λ= 488 nm, providing an example of such sub-Brownian metrology with ∼λ/5,300 precision. To localize the nanowire, we employ a deep-learning analysis of the scattering of topologically structured light, which is highly sensitive to the nanowire’s position. This non-invasive metrology with absolute errors down to a fraction of the typical size of an atom, opens a range of opportunities to study picometre-scale phenomena with light.

Published
2023
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24. “Bamanaya is so difficult to leave behind”

Author

MacDonald, Kevin C

Abstract

Islamization in Mande West Africa gradually accompanied the expansion of mercantile groups and was surprisingly accommodating via syncretic processes with local spiritual traditions. Elites of the Empire of Mali were amongst the first to embrace Islam and mediate between it and indigenous earth religions. Yet this process was patchy across different cultural sectors and from the seventeenth century onwards there were upswellings of Bamanaya, earth religions, in open conflict with waves of Islamic jihadism (e.g. the Umarian movement). Thus, historic polities could retain both mosques and non-Islamic shrines, and maraboutic practices incorporated forms of local magic. This article considers results from “Project Segou”: historical and archaeological fieldwork undertaken between 2005 and 2013 in the Segou region of Mali, stretching approximately from Sinsanni in the east to Nyamina in the west. As a heartland of the Empire of Mali (c. AD 1235–1500) and the core of Bamana Segou (c. AD 1700–1861), its oral and archaeological sources inform our deep time appreciation of ideological and spiritual change at the margins of the Middle Niger from the thirteenth through nineteenth centuries AD.

Published
2023
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25. Photonic metamaterial analogue of a continuous time crystal

Author

Liu, Tongjun, Ou, Jun-Yu, MacDonald, Kevin F., and Zheludev, Nikolay I.

Abstract

Time crystals are an eagerly sought phase of matter with broken time-translation symmetry. Quantum time crystals with discretely broken time-translation symmetry have been demonstrated in trapped ions, atoms and spins whereas continuously broken time-translation symmetry has been observed in an atomic condensate inside an optical cavity. Here we report that a classical metamaterial nanostructure, a two-dimensional array of plasmonic metamolecules supported on flexible nanowires, can be driven to a state possessing all of the key features of a continuous time crystal: continuous coherent illumination by light resonant with the metamolecules’ plasmonic mode triggers a spontaneous phase transition to a superradiant-like state of transmissivity oscillations, resulting from many-body interactions among the metamolecules, characterized by long-range order in space and time. The phenomenon is of interest to the study of dynamic classical many-body states in the strongly correlated regime and applications in all-optical modulation, frequency conversion and timing.

Published
2023
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40. Optical Control of Nanomechanical Brownian Motion Eigenfrequencies in Metamaterials

Author

Li, Jinxiang, MacDonald, Kevin F., and Zheludev, Nikolay I.

Abstract

Nanomechanical photonic metamaterials provide a wealth of active switching, nonlinear, and enhanced light-matter interaction functionalities by coupling optically and mechanically resonant subsystems. Thermal (Brownian) motion of the nanostructural components of such metamaterials leads to fluctuations in optical properties, which may manifest as noise, but which also present opportunity to characterize performance and thereby optimize design at the level of individual nanomechanical elements. We show that nanomechanical motion in an all-dielectric metamaterial ensemble of silicon-on-silicon-nitride nanowires can be controlled by light at sub-μW/μm2intensities. Induced changes in nanowire temperature of just a few Kelvin and nonthermal optical forces generated within the structure change the few-MHz Eigenfrequencies and/or picometric displacement amplitudes of motion, and thereby metamaterial transmission. The tuning mechanism can provide active control of frequency response in photonic metadevices and may serve as a basis for bolometric, mass, and micro/nanostructural stress sensing.

Published
2022
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41. Deep-Learning-Assisted Focused Ion Beam Nanofabrication

Author

Buchnev, Oleksandr, Grant-Jacob, James A., Eason, Robert W., Zheludev, Nikolay I., Mills, Ben, and MacDonald, Kevin F.

Abstract

Focused ion beam (FIB) milling is an important rapid prototyping tool for micro- and nanofabrication and device and materials characterization. It allows for the manufacturing of arbitrary structures in a wide variety of materials, but establishing the process parameters for a given task is a multidimensional optimization challenge, usually addressed through time-consuming, iterative trial-and-error. Here, we show that deep learning from prior experience of manufacturing can predict the postfabrication appearance of structures manufactured by focused ion beam (FIB) milling with >96% accuracy over a range of ion beam parameters, taking account of instrument- and target-specific artifacts. With predictions taking only a few milliseconds, the methodology may be deployed in near real time to expedite optimization and improve reproducibility in FIB processing.

Published
2022
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42. MRI and muscle enzymes do not support the diagnosis of local anesthetic myotoxicity: a descriptive case series.

Author

Mahyar, Lauren, Neal, Joseph M., Blackmore, C. Craig, Jackson, Dane W., Hanson, Neil A., MacDonald, Kevin M., Warren, Daniel, and Verdin, Peter J.

Abstract

Background The presence of thigh muscle edema as characterized by increased signal intensity on MRI has been used to support the diagnosis of presumed local anesthetic-induced myotoxicity reported after total knee arthroplasty (TKA) with continuous adductor canal block (CACB). However, neither postoperative baseline imaging appearance nor muscle enzyme values have been described in conjunction with this clinical scenario. Thus, the usefulness of MRI or enzymatic biomarkers of muscle injury for supporting the diagnosis of local anesthetic myotoxicity is unknown. Methods This descriptive case series documents postoperative MRI appearance of the ipsilateral upper leg, plus preoperative and postoperative creatine phosphokinase and aldolase values in volunteer patients who underwent uncomplicated TKA with CACB. Results In 27 volunteer patients with no postsurgical evidence of clinically relevant myotoxicity, anterior thigh muscle edema was universally evident on imaging (n=12) and muscle enzyme values (n=19) were normal or only slightly elevated. Conclusions The non-specificity of these findings suggests that MRI and near normal muscle enzyme levels are of limited diagnostic value when there is clinical suspicion of local anesthetic myotoxicity in the setting of TKA with CACB. [ABSTRACT FROM AUTHOR]

Published
2021
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