68 research outputs found
Composition law for polarizers
The polarization process when polarizers act on an optical field is studied.
We give examples for two kinds of polarizers. The first kind presents an
anisotropic absorption - as in a polaroid film - and the second one is based on
total reflection at the interface with a birefringent medium. Using the Stokes
vector representation, we determine explicitly the trajectories of the wave
light polarization during the polarization process. We find that such
trajectories are not always geodesics of the Poincar\'e sphere as it is usually
thought. Using the analogy between light polarization and special relativity,
we find that the action of successive polarizers on the light wave polarization
is equivalent to the action of a single resulting polarizer followed by a
rotation achieved for example by a device with optical activity. We find a
composition law for polarizers similar to the composition law for noncollinear
velocities in special relativity. We define an angle equivalent to the
relativistic Wigner angle which can be used to quantify the quality of two
composed polarizers.Comment: 23 pages, 9 figures, accepted for publication in Physical Review
Sending femtosecond pulses in circles: highly non-paraxial accelerating beams
We use caustic beam shaping on 100 fs pulses to experimentally generate
non-paraxial accelerating beams along a 60 degree circular arc, moving
laterally by 14 \mum over a 28 \mum propagation length. This is the highest
degree of transverse acceleration reported to our knowledge. Using diffraction
integral theory and numerical beam propagation simulations, we show that
circular acceleration trajectories represent a unique class of non-paraxial
diffraction-free beam profile which also preserves the femtosecond temporal
structure in the vicinity of the caustic
Arbitrary non-paraxial accelerating periodic beams and spherical shaping of light
We report the observation of arbitrary accelerating beams designed using a
non-paraxial description of optical caustics. We use a spatial light
modulator-based setup and techniques of Fourier optics to generate circular and
Weber beams subtending over 95 degrees of arc. Applying a complementary binary
mask also allows the generation of periodic accelerating beams taking the forms
of snake-like trajectories, and the application of a rotation to the caustic
allows the first experimental synthesis of optical accelerating beams upon the
surface of a sphere in three dimensions.Comment: 4 pages, 4 figures articl
Characterization of seed proanthocyanidins of thirty-two red and white hybrid grape varieties
Grape seed extracts are known for their beneficial effects on health and on cardiovascular diseases due to antioxidant activity and the free radical-scavenging properties of proanthocyanidins (PAs). Moreover, grape seed tannins are used in oenology as additives to improve the organoleptic characteristics of wines, and for the clarification of must and wines. PAs in seed extract of 32 hybrid and three V. vinifera grape varieties were characterized by MALDI-TOF mass spectrometry. Signals of 148 compounds were identified as [M+H]+, [M+Na]+ and [M+K]+ adducts of B-type and A-type PAs formed from catechin/epicatechin subunits up to undecamers and with galloylation degree 0-7. The number-average molecular weight (Mn) of the samples, a parameter correlated with the molecular weight of polymers, and the polyphenolic content of extract, were also determined. Profiles of the hybrid grape varieties were compared with those of three V. vinifera samples studied as references. 'Terzi 108-6' showed high content of antioxidant polyphenols and 'Seyve Villard 12-390' higher content of higher oligomers. These two grape varieties are therefore potentially very interesting as sources of antioxidants and tannins for nutraceutical and oenological uses
Security challenges of small cell as a service in virtualized mobile edge computing environments
Research on next-generation 5G wireless networks is currently attracting a lot of attention in both academia and industry. While 5G development and standardization activities are still at their early stage, it is widely acknowledged that 5G systems are going to extensively rely on dense small cell deployments, which would exploit infrastructure and network functions virtualization (NFV), and push the network intelligence towards network edges by embracing the concept of mobile edge computing (MEC). As security will be a fundamental enabling factor of small cell as a service (SCaaS) in 5G networks, we present the most prominent threats and vulnerabilities against a broad range of targets. As far as the related work is concerned, to the best of our knowledge, this paper is the first to investigate security challenges at the intersection of SCaaS, NFV, and MEC. It is also the first paper that proposes a set of criteria to facilitate a clear and effective taxonomy of security challenges of main elements of 5G networks. Our analysis can serve as a staring point towards the development of appropriate 5G security solutions. These will have crucial effect on legal and regulatory frameworks as well as on decisions of businesses, governments, and end-users
Palladacyclopentadienyl complexes bearing purine-based N-heterocyclic carbenes: A new class of promising antiproliferative agents against human ovarian cancer
A complete protocol for the synthesis of new palladacyclopentadienyl complexes with purineâ based carbenes as supporting ligands is described. The new organometallic compounds were exhaustively characterized using NMR and infrared spectroscopies and elemental analysis. The singleâ crystal Xâ ray structure of complex 2b coordinating also a triphenylphosphine was resolved. Some of these complexes showed an antiproliferative activity comparable to or better than that of cisplatin on two human ovarian cancer lines: A2780 (cisplatinâ sensitive) and A2780cis (cisplatinâ resistant). Moreover, for complexes 2 and 3 (coordinating one purineâ based Nâ heterocyclic carbene ligand and one phosphine) the cytotoxicity is associated with an evident induction of apoptosis. Finally, complexes 3 , bearing one purineâ based Nâ heterocyclic carbene ligand and one 1,3,5â triazaâ 7â phosphaadamantane, proved practically inactive on nonâ tumour fibroblast cells (MRCâ 5)
Void reactivity coefficient benchmark results for a 10x10 BWR assembly in the full 0-100% void fraction range
A boiling water reactor SVEA-96+ fresh fuel lattice has been used as the basis for a benchmark study of the void reactivity coefficient at assembly level in the full voidage range. Results have been obtained using the deterministic codes CASMO-4, HELIOS, PHOENIX, BOXER and the probabilistic code MCNP4C, combined for almost all cases with different cross section libraries. A statistical analysis of the results obtained showed that the void reactivity coefficient tends to become less negative beyond 80% void and that the discrepancies between codes tend to increase from less than 15% at voidages lower than 40% to more than 25% at voidages higher than 70%. The void reactivity coefficient results and the corresponding differences between codes were isotopically decomposed to interpret discrepancies. The isotopic decomposition shows that the minimum observed in the void reactivity coefficient between 80% and 90% void is largely due to the decrease in the relative importance of the 157Gd(n, ) rate with increasing voidage, and that the fundamental discrepancies between codes or libraries are mainly governed by the different predictions of the 238U(n, ) variation with voidage. [All rights reserved Elsevier]
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