Absorption modes of Möbius strip resonators

This is the final version. Available on open access from Nature Research via the DOI in this record. In this work, the electromagnetic response of a mathematically interesting shape-a Möbius strip-is presented, along with a ring resonator for comparison. Both resonators consist of a central lossy dielectric layer bounded by perfectly conducting layers. For the case of the Möbius strips, the computational results show that there are a family of half-integer wavelength modes within the dielectric layer. These additional modes result in increased absorption, and a corresponding reduction in the radar cross section. Interestingly, rotational scans show that these modes can be excited over a large angular range. This investigation gives an understanding of the electromagnetic response of these structures, paving the way for future experiments on Möbius strip resonators.Engineering and Physical Sciences Research Council (EPSRC

Covert Images Using Surface Plasmon-Mediated Optical Polarization Conversion

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this recordCovert optical signatures are a vital element in anticounterfeiting technologies. Plasmonic surfaces offer a means of manipulating the properties of light including the realization of colored pixels and images. In this work, concealed images with accurate color reproduction using plasmonic pixel arrays are demonstrated. The spectral and spatial control of optical polarization conversion is accomplished by tailoring the interaction of light with surface plasmons through the design and arrangement of surface nanostructures. The latent image is revealed using a polarization-sensitive optical system, which represents a means for the authentication of security features that can be created using these nanostructured devices. A red-green-blue color space is defined containing a wide gamut of chromaticities, enabling comprehensive full-color image capability. The device concept extends the functionality of a polarization-dependent plasmonic response to realize the encoding of a color image in covert form.This work was supported by the UK Engineering and Physical Sciences Research Council (EPSRC) Knowledge Transfer Account programme grant EP/H50012X/1, and by QinetiQ Ltd

Efficient mm-wave photomodulation via coupled Fabry–Perot cavities

This is the author accepted manuscript. The final version is available from AIP Publishing via the DOI in this recordData availability: The data that support the findings of this study are available from the corresponding author upon reasonable request.An efficient mm-wave photomodulator is designed based on coupled Fabry–Perot modes in a low-lifetime silicon wafer and an adjacent cavity formed from a transparent reflector, such as indium tin oxide. The modulation of a reflected beam using this coupled-cavity design is increased by a factor of 7 compared with that from an isolated silicon wafer, while also introducing a degree of tunability and maintaining low angular dispersion. For the particular design built and tested, a modulation of 32% is achieved for an extremely low optical illumination of just 0.006W/cm2 and with a maximum operation rate of more than 3 kHz. The large increase in modulation, coupled with the flexibility of the design and the fact that all components can be industrially manufactured, makes this photomodulator a promising candidate for many communication, imaging, and sensing applications.Engineering and Physical Sciences Research Council (EPSRC)QinetiQ Ltd

Effective-periodicity effects in Fibonacci slot arrays (article)

This is the final version. Available from the American Physical Society via the DOI in this record. The data that support the findings of this study are available from the corresponding author upon reasonable request.The dataset associated with this article is available in ORE at: https://doi.org/10.24378/exe.3783In this Letter, the transmission properties of a nonperiodic array of slots arranged in the form of a Fibonacci sequence are investigated. By arranging the slots in this manner, an additional periodicity can be utilized, resulting in corresponding resonance features in the transmitted signal. By investigating the transmission response of a perforated metallic sheet over a broad frequency range (6–40 GHz), it is shown that this simple one-dimensional chain supports two periodicities, one due to the regular periodic separation and one due to average spacing—which is related to the golden ratio. This response replicates the resonant behavior of a two-dimensional periodic array with a single nonperiodic array also creating new families of diffraction lobes in the far-field region.Engineering and Physical Sciences Research CouncilEngineering and Physical Sciences Research CouncilMCIN/AEI/10.13039/50110001103

Multi-resonant tessellated anchor-based metasurfaces

This is the final version. Available from Nature Research via the DOI in this record. Data availability: The research data supporting this publication are openly available from the University of Exeter’s institutional repository at: https://doi.org/10.24378/exe.4504.In this work, a multi-resonant metasurface that can be tailored to absorb microwaves at one or more frequencies is explored. Surface shapes based on an ‘anchor’ motif, incorporating hexagonal, square and triangular-shaped resonant elements, are shown to be readily tailorable to provide a targeted range of microwave responses. A metasurface consisting of an etched copper layer, spaced above a ground plane by a thin (<1/10th of a wavelength) low-loss dielectric is experimentally characterised. The fundamental resonances of each shaped element are exhibited at 4.1 GHz (triangular), 6.1 GHz (square) and 10.1 GHz (hexagonal), providing the potential for single- and multi-frequency absorption across a range that is of interest to the food industry. Reflectivity measurements of the metasurface demonstrate that the three fundamental absorption modes are largely independent of incident polarization as well as both azimuthal and elevation angles.Engineering and Physical Sciences Research Council (EPSRC)PepsiC

Super-resolution imaging for sub-IR frequencies based on total internal reflection

This is the final version. Available on open access from the Optical Society of America via the DOI in this recordFor measurements designed to accurately determine layer thickness, there is a natural trade-off between sensitivity to optical thickness and lateral resolution due to the angular ray distribution required for a focused beam. We demonstrate a near-field imaging approach that enables subwavelength lateral resolution in images with contrast dependent on optical thickness. We illuminate a sample in a total internal reflection geometry, with a photoactivated spatial modulator in the near field, which allows optical thickness images to be computationally reconstructed in a few seconds. We demonstrate our approach at 140 GHz (wavelength 2.15 mm), where images are normally severely limited in spatial resolution, and demonstrate mapping of optical thickness variation in inhomogeneous biological tissues.Engineering and Physical Sciences Research Council (EPSRC)Royal Academy of Engineering (RAE)European Research Council (ERC

Prenatal Vitamin D Supplementation and Child Respiratory Health: A Randomised Controlled Trial

PMCID: PMC3691177This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Belowground DNA-based techniques: untangling the network of plant root interactions

Contains fulltext : 91591.pdf (publisher's version ) (Closed access)7 p

The effects of fruit smoothies on enamel erosion

Objectives: This prospective, randomised in vitro study was to investigate the pH and titratable acidity of fruit smoothie drinks and to assess the effect of these drinks on enamel erosion. Method: Fifty enamel slabs were divided into five groups which were allocated to the sample solutions groups: Innocent® smoothie strawberries and bananas (SB), Innocent® smoothie mangoes and passion fruit (MP) and Diet Coke. Distilled deionised water (DD) was used as negative control and citric acid 0.3 % as positive control. All the slabs were subjected to a 21-day pH cycling regime involving 2 min of immersions, five times a day with appropriate remineralization periods in between. Measurement of surface loss was assessed using profilometry. Independent sample t tests were used to compare mean. Results: The titratable acidity for both test smoothies were 3.5-4 times more than that needed to neutralise Diet Coke and citric acid 0.3 %. The pH of SB, MP smoothie and Diet Coke was found to be 3.73, 3.59 and 2.95, respectively. MP smoothie caused the greatest amount of surface loss followed by Diet Coke. Both smoothies were found to cause significant surface loss. MP smoothie resulted in significantly higher surface loss compared with MB smoothie and citric acid 3 %. Conclusion: The smoothies tested were acidic and had high titratable acidity. They produced a significant erosion of enamel in vitro. The results of this study suggest that there should be increased awareness of the erosive effects of smoothies especially as their consumption seems to be on the increase

Characteristics of patients with venous thromboembolism and atrial fibrillation in Venezuela

<p>Abstract</p> <p>Background</p> <p>Studies describing venous thromboembolic event (VTEE) and atrial fibrillation (AF) in South American populations are limited. The aim of this cross-sectional study was to describe the characteristics of Venezuelan patients admitted and treated for these conditions.</p> <p>Methods</p> <p>A retrospective medical record review of 1397 consecutive patients admitted to three private hospitals or clinics between January 2000 and December 2005 was performed. Data was collected on demographics, anthropometrics, hospital visit, comorbidities and treatment.</p> <p>Results</p> <p>Among 401 VTEE and 996 AF patients, men were more likely to have AF (58%) while more women experienced a VTEE (58%). Most patients were admitted via the emergency room (87%) and had only one event during the study period (83%). Common comorbidities included hypertension (46%), heart failure (17%), diabetes (12%) and congestive heart failure (11%). Characteristics of Venezuelan patients with VTEE and AF are similar to that reported in the literature for other populations.</p> <p>Conclusions</p> <p>These results provide background characteristics for future studies assessing risk factors for AF and VTEE in South American populations.</p