Micromagnetic Simulations of Ferromagnetic Rings

Thin nanomagnetic rings have generated interest for fundamental studies of magnetization reversal and also for their potential in various applications, particularly as magnetic memories. They are a rare example of a geometry in which an analytical solution for the rate of thermally induced magnetic reversal has been determined, in an approximation whose errors can be estimated and bounded. In this work, numerical simulations of soft ferromagnetic rings are used to explore aspects of the analytical solution. The evolution of the energy near the transition states confirms that, consistent with analytical predictions, thermally induced magnetization reversal can have one of two intermediate states: either constant or soliton-like saddle configurations, depending on ring size and externally applied magnetic field. The results confirm analytical predictions of a transition in thermally activated reversal behavior as magnetic field is varied at constant ring size. Simulations also show that the analytic one dimensional model continues to hold even for wide rings

Lead identification and structure-activity relationships of heteroarylpyrazole arylsulfonamides as allosteric CC-chemokine receptor 4 (CCR4) antagonists

A knowledge-based library of aryl 2,3-dichlorophenylsulfonamides was synthesised and screened as human CCR4 antagonists, in order to identify a suitable hit for the start of a lead-optimisation programme. X-ray diffraction studies were used to identify the pyrazole ring as a moiety that could bring about intramolecular hydrogen bonding with the sulfonamide NH and provide a clip or orthogonal conformation that was believed to be the preferred active conformation. Replacement of the core phenyl ring with a pyridine, and replacement of the 2,3-dichlorobenzenesulfonamide with 5- chlorothiophenesulfonamide provided compound 33 which has excellent physicochemical properties and represents a good starting point for a lead optimisation programme. Electronic structure calculations indicated that the preference for the clip or orthogonal conformation found in the small molecule crystal structures of 7 and 14 was in agreement with the order of potency in the biological assay

Thermal Stability of the Magnetization in Perpendicularly Magnetized Thin Film Nanomagnets

Understanding the stability of thin film nanomagnets with perpendicular magnetic anisotropy (PMA) against thermally induced magnetization reversal is important when designing perpendicularly magnetized patterned media and magnetic random access memories. The leading-order dependence of magnetization reversal rates are governed by the energy barrier the system needs to surmount in order for reversal to proceed. In this paper we study the reversal dynamics of these systems and compute the relevant barriers using the string method of E, Vanden-Eijnden, and Ren. We find the reversal to be often spatially incoherent; that is, rather than the magnetization flipping as a rigid unit, reversal proceeds instead through a soliton-like domain wall sweeping through the system. We show that for square nanomagnetic elements the energy barrier increases with element size up to a critical length scale, beyond which the energy barrier is constant. For circular elements the energy barrier continues to increase indefinitely, albeit more slowly beyond a critical size. In both cases the energy barriers are smaller than those expected for coherent magnetization reversal.Comment: 5 pages, 4 Figure

Stability of 2pi domain walls in ferromagnetic nanorings

The stability of 2pi domain walls in ferromagnetic nanorings is investigated via calculation of the minimum energy path that separates a 2pi domain wall from the vortex state of a ferromagnetic nanoring. Trapped domains are stable when they exist between certain types of transverse domain walls, i.e., walls in which the edge defects on the same side of the magnetic strip have equal sign and thus repel. Here the energy barriers between these configurations and vortex magnetization states are obtained using the string method. Due to the geometry of a ring, two types of 2pi walls must be distinguished that differ by their overall topological index and exchange energy. The minimum energy path corresponds to the expulsion of a vortex. The energy barrier for annihilation of a 2pi wall is compared to the activation energy for transitions between the two ring vortex states.Comment: 4 pages, 2 figure

A Comprehensive Survey on RF Energy Harvesting: Applications and Performance Determinants

\ua9 2022 by the authors. Licensee MDPI, Basel, Switzerland.There has been an explosion in research focused on Internet of Things (IoT) devices in recent years, with a broad range of use cases in different domains ranging from industrial automation to business analytics. Being battery-powered, these small devices are expected to last for extended periods (i.e., in some instances up to tens of years) to ensure network longevity and data streams with the required temporal and spatial granularity. It becomes even more critical when IoT devices are installed within a harsh environment where battery replacement/charging is both costly and labour intensive. Recent developments in the energy harvesting paradigm have significantly contributed towards mitigating this critical energy issue by incorporating the renewable energy potentially available within any environment in which a sensor network is deployed. Radio Frequency (RF) energy harvesting is one of the promising approaches being investigated in the research community to address this challenge, conducted by harvesting energy from the incident radio waves from both ambient and dedicated radio sources. A limited number of studies are available covering the state of the art related to specific research topics in this space, but there is a gap in the consolidation of domain knowledge associated with the factors influencing the performance of RF power harvesting systems. Moreover, a number of topics and research challenges affecting the performance of RF harvesting systems are still unreported, which deserve special attention. To this end, this article starts by providing an overview of the different application domains of RF power harvesting outlining their performance requirements and summarizing the RF power harvesting techniques with their associated power densities. It then comprehensively surveys the available literature on the horizons that affect the performance of RF energy harvesting, taking into account the evaluation metrics, power propagation models, rectenna architectures, and MAC protocols for RF energy harvesting. Finally, it summarizes the available literature associated with RF powered networks and highlights the limitations, challenges, and future research directions by synthesizing the research efforts in the field of RF energy harvesting to progress research in this area

Spatial resolution of drug crystallisation in the skin by X-ray micro-computed tomography

Drug crystallisation in the skin is recognised as a significant problem in topical and transdermal drug delivery. Our recent investigations provided new evidence of drug crystallisation in the skin, however, confirming the precise location of crystals remains challenging. Of note, most approaches used have required disruption of the membrane by tape stripping, with crystal detection limited to the superficial skin layers. Hence, a non-destructive method for complete spatial resolution of crystallised drug in skin is still lacking. In this communication, we report the application of X-ray micro-computed tomography (microCT) to examine drug crystallisation in mammalian skin ex vivo. Permeation studies of a saturated solution of diclofenac sodium were conducted in porcine skin; subsequently, tissue samples were scanned using microCT to generate 2D and 3D maps. A layer of drug crystals was observed on the skin surface; microCT maps also confirmed the distribution of drug crystals up to a skin depth of 0.2 – 0.3 mm. MicroCT also allowed the identification of drug crystallisation as a distinct and confirmed event in the skin and as an extension from drug crystals formed on the skin. These preliminary results confirm the potential of microCT to study this important phenomenon in topical and transdermal drug delivery

Tracking Development Progress and Evaluating Development Partnerships in the Post-2015 Era

Wilton Park convened this meeting to shine light on the post-2015 journey towards the Sustainable Development Goals (SDGs) and the role that evaluation should play in tracking progress towards them. This event brought together decision makers, scholars and evaluators from around the world. It discussed policy and evaluation challenges posed by the aspirational nature ofthe SDGs formally endorsed by 193 heads of states in September 2015. While much depends on monitoring progress of the 17 goals and 169 targets through no less than 230 indicators, evaluation potentially needs to provide understanding of what works, how, for whom, under which circumstances, to achieve progress. This Wilton Park meeting sought to address someof the key challenges affecting partnerships and evaluation of the SDGs, including policy priorities, the need for new approaches, tools and methods, support for country-level evaluations and follow-up