On the transformations generated by the electromagnetic spin and orbital angular momentum operators

We present a study of the properties of the transversal "spin angular momentum" and "orbital angular momentum" operators. We show that the "spin angular momentum" operators are generators of spatial translations which depend on helicity and frequency and that the "orbital angular momentum" operators generate transformations which are a sequence of this kind of translations and rotations. We give some examples of the use of these operators in light matter interaction problems. Their relationship with the helicity operator allows to involve the electromagnetic duality symmetry in the analysis. We also find that simultaneous eigenstates of the three "spin" operators and parity define a type of standing modes which has been recently singled out for the interaction of light with chiral molecules. With respect to the relationship between "spin angular momentum", polarization, and total angular momentum, we show that, except for the case of a single plane wave, the total angular momentum of the field is decoupled from its vectorial degrees of freedom even in the regime where the paraxial approximation holds. Finally, we point out a relationship between the three "spin" operators and the spatial part of the Pauli-Lubanski four vector

Necessary symmetry conditions for the rotation of light

Two conditions on symmetries are identified as necessary for a linear scattering system to be able to rotate the linear polarisation of light: Lack of at least one mirror plane of symmetry and electromagnetic duality symmetry. Duality symmetry is equivalent to the conservation of the helicity of light in the same way that rotational symmetry is equivalent to the conservation of angular momentum. When the system is a solution of a single species of particles, the lack of at least one mirror plane of symmetry leads to the familiar requirement of chirality of the individual particle. With respect to helicity preservation, according to the analytical and numerical evidence presented in this paper, the solution preserves helicity if and only if the individual particle itself preserves helicity. However, only in the particular case of forward scattering the helicity preservation condition on the particle is relaxed: We show that the random orientation of the molecules endows the solution with an effective rotational symmetry; at its turn, this leads to helicity preservation in the forward scattering direction independently of any property of the particle. This is not the case for a general scattering direction. These results advance the current understanding of the phenomena of molecular optical activity and provide insight for the design of polarisation control devices at the nanoscale.Comment: 17 pages, 3 figure

Perennialism Through the Lens of Otherness

Otherness has been a subject of the utmost relevance for continental philosophy since the beginning of the 20th century, constituting what might be characterized as an otherness turn. Otherness is here understood as the awareness that one has that other beings or things have their own separate beingness that is not subsumed within oneself. Its essential role in human relations permits the creation of a critical perspective of analysis, a “lens of otherness.” Applying this lens to perennialism up through its latest iterations reveals some problematic aspects of this approach. By contrast, participatory thought may be a more “otherness compliant” alternative to perennialism. Whereas perennialism can be seen as being geared toward theoretical unification, participatory approaches are arguably guided by an ethos of otherness. Otherness is thus advanced as a relevant aspect in the debate on perennialism, and participatory thought is proposed as a more viable philosophical frame for transpersonal studies

Far-field measurements of vortex beams interacting with nanoholes

We measure the far-field intensity of vortex beams going through nanoholes. The process is analyzed in terms of helicity and total angular momentum. It is seen that the total angular momentum is preserved in the process, and helicity is not. We compute the ratio between the two transmitted helicity components, $\gamma_{m,p}$. We observe that this ratio is highly dependent on the helicity ($p$) and the angular momentum ($m$) of the incident vortex beam in consideration. Due to the mirror symmetry of the nanoholes, we are able to relate the transmission properties of vortex beams with a certain helicity and angular momentum, with the ones with opposite helicity and angular momentum. Interestingly, vortex beams enhance the $\gamma_{m,p}$ ratio as compared to those obtained by Gaussian beams

Assessment of left ventricular diastolic function by MR: why, how and when

Cardiovascular magnetic resonance (CMR), a valuable non-invasive technique for the evaluation of the cardiovascular system, has already been accepted as the "gold standard" for the assessment of systolic function. The assessment of diastolic function is important not only for diagnosis purposes, but also in terms of prognosis. ECG-triggering phase-contrast (PC) CMR allows the routine assessment of diastolic function by measuring the transmitral and pulmonary venous flow with high accuracy and reproducibility, using morphological and quantitative parameters similar to those obtained by transthoracic echocardiography, which are so familiar to general cardiologists. Therefore, the increasing role of CMR in the assessment of the cardiovascular system requires a greater awareness and knowledge of this condition by radiologists. The aim of this study is to review the main mechanisms and common causes of left ventricle diastolic dysfunction, provide a practical approach for the assessment of LV diastolic function and illustrate the different degrees of diastolic dysfunction

The effect of the aphid sex pheromone on the aphid Myzus persicae and its parasitoid Aphidius colemani

Aphids remain an enormous threat to the sustainability of crops in glasshouse and field environments around the world. It is known that the aphid sex pheromone is used as a kairomone by its natural enemies, such as parasitoids. The focus of this research was how the aphid sex pheromone component, (4aS,7S,7aR)-nepetalactone, affects a host, its parasitoid and the host-parasitoid interaction in a tritrophic system. A model system of Chinese cabbage Brassica rapa sp. Pekinensis Cv. Wong bok, the peach-potato aphid Myzus persicae and the generalist parasitoid Aphidius colemani is applied with a particular emphasis on understanding parasitoid foraging and how it may be affected, and potentially manipulated, by nepetalactone.Firstly, it was demonstrated that asexual M. persicae are capable of detecting the sex pheromone components, despite their components having no previously known ecological function in parthenogenetic populations. Although it was found that they avoid the odour in high concentrations, it was concluded that performance on an individual or population level were unlikely to be affected. The ability of the parasitoid A. colemani to detect nepetalactone was confirmed at the electrophysiological level.Nepetalactone did not elicit any behavioural response when presented in isolation but was found to increase retention of the parasitoid within a patch if other host cues were also present. It was found that Nepeta cataria oil, from which nepetalactone can be isolated, increased the success of parasitoid oviposition in the host. To enhance parasitoid foraging, it was investigated whether learning was possible with nepetalactone; an odour already known to elicit an innate response. Learning through emergence conditioning was ineffective in altering parasitoid behaviour; however, ovipositional experience did induce a change in foraging patterns. This change in foraging pattern did not translate to more effective host location when tested in the laboratory, which led the research towards experimentation in a more complex spatialtemporal environment. Nepetalactone, or the learning of nepetalactone, were not found to have an effect on parasitoid success at this scale. It was found that the introduction of parasitoids into a glasshouse environment reduced aphid population growth at a rate disproportionate to the rate of mummification. This highlighted the importance of indirect consequences of parasitoid visitation on aphid population control. In a separate assay it was identified that aphid population size affects plant fitness, such that smaller aphid populations result in greater plant fitness, thus demonstrating benefits of parasitoids in biological control which are often overlooked.This work provided a greater insight into the role of nepetalactone in a tritrophic system and how odours may be used by parasitoids during foraging. Finally, the key findings of this study are discussed and the possible direction of future work. A new interpretation of parasitoid foraging is discussed, by the integration of information provided by this study and knowledge generated by previous work

Computing Safe Contention Bounds for Multicore Resources with Round-Robin and FIFO Arbitration

Numerous researchers have studied the contention that arises among tasks running in parallel on a multicore processor. Most of those studies seek to derive a tight and sound upper-bound for the worst-case delay with which a processor resource may serve an incoming request, when its access is arbitrated using time-predictable policies such as round-robin or FIFO. We call this value upper-bound delay ( ubd ). Deriving trustworthy ubd statically is possible when sufficient public information exists on the timing latency incurred on access to the resource of interest. Unfortunately however, that is rarely granted for commercial-of-the-shelf (COTS) processors. Therefore, the users resort to measurement observations on the target processor and thus compute a “measured” ubdm . However, using ubdm to compute worst-case execution time values for programs running on COTS multicore processors requires qualification on the soundness of the result. In this paper, we present a measurement-based methodology to derive a ubdm under round-robin (RoRo) and first-in-first-out (FIFO) arbitration, which accurately approximates ubd from above, without needing latency information from the hardware provider. Experimental results, obtained on multiple processor configurations, demonstrate the robustness of the proposed methodology.The research leading to this work has received funding from: the European Union’s Horizon 2020 research and innovation programme under grant agreement No 644080(SAFURE); the European Space Agency under Contract 789.2013 and NPI Contract 40001102880; and COST Action IC1202, Timing Analysis On Code-Level (TACLe). This work has also been partially supported by the Spanish Ministry of Science and Innovation under grant TIN2015-65316-P. Jaume Abella has been partially supported by the MINECO under Ramon y Cajal postdoctoral fellowship number RYC-2013-14717. The authors would like to thanks Paul Caheny for his help with the proofreading of this document.Peer ReviewedPostprint (author's final draft