Design of a 3D photonic band gap cavity in a diamond-like inverse woodpile photonic crystal

We theoretically investigate the design of cavities in a three-dimensional (3D) inverse woodpile photonic crystal. This class of cubic diamond-like crystals has a very broad photonic band gap and consists of two perpendicular arrays of pores with a rectangular structure. The point defect that acts as a cavity is centred on the intersection of two intersecting perpendicular pores with a radius that differs from the ones in the bulk of the crystal. We have performed supercell bandstructure calculations with up to $5 \times 5 \times 5$ unit cells. We find that up to five isolated and dispersionless bands appear within the 3D photonic band gap. For each isolated band, the electric-field energy is localized in a volume centred on the point defect, hence the point defect acts as a 3D photonic band gap cavity. The mode volume of the cavities resonances is as small as 0.8 $\lambda^{3}$ (resonance wavelength cubed), indicating a strong confinement of the light. By varying the radius of the defect pores we found that only donor-like resonances appear for smaller defect radius, whereas no acceptor-like resonances appear for greater defect radius. From a 3D plot of the distribution of the electric-field energy density we conclude that peaks of energy found in sharp edges situated at the point defect, similar to how electrons collect at such features. This is different from what is observed for cavities in non-inverted woodpile structures. Since inverse woodpile crystals can be fabricated from silicon by CMOS-compatible means, we project that single cavities and even cavity arrays can be realized, for wavelength ranges compatible with telecommunication windows in the near infrared.Comment: 11 figure

Signature of a three-dimensional photonic band gap observed on silicon inverse woodpile photonic crystals

We have studied the reflectivity of CMOS-compatible three-dimensional silicon inverse woodpile photonic crystals at near-infrared frequencies. Polarization-resolved reflectivity spectra were obtained from two orthogonal crystal surfaces corresponding to 1.88 pi sr solid angle. The spectra reveal broad peaks with high reflectivity up to 67 % that are independent of the spatial position on the crystals. The spectrally overlapping reflectivity peaks for all directions and polarizations form the signature of a broad photonic band gap with a relative bandwidth up to 16 %. This signature is supported with stopgaps in plane wave bandstructure calculations and with the frequency region of the expected band gap.Comment: 9 pages, 5 figure

Résection trans urétrale de la prostate : première expérience à Bukavu, RD Congo: Transurethral resection of the prostate: pilot experience in Bukavu, DR Congo

Context and objective. Despite its large use as alternative to open surgical adenomectomy, transurethral resection of the prostate (TURP) is still poorly performed in many African countries. The purpose of this study was to describe a pilotTURP experience in Bukavu. Methods.This retrospective study included 159 patients (average age: 68 ± 8.5 years) with benign prostatic hypertrophy (BPH), treated at three medical centres in Bukavu between February 2014 andFebruary 2017. Socio-demographic, clinical, and ultrasound data were recorded, and comorbidities and complications reported. Each patient was questionned about treatment received before surgery. Results. The average prostatic volume was 53.2 ± 22 grams. All patients were severelysymptomatic (mean International Prostate Symptoms Score (IPSS) 26.8 ± 5.8) and severely bored (mean quality of life score (QOL) 6.2 ± 0.8).Hypertension (42%) and type 2 diabetes (41%) were the most common comorbidities. The most frequent complications of BPH were urinary tractinfection (44%) and urinary retention (40%). Prior to hospital admission, 60% of patients used traditional medicine. Conclusion.This study has revealed a late reference of patients to the hospital, when the illness is already in advanced stage with complications. There is a need of implementing educational measures targeting early detection and reference of patients with BPH in this area. Résumé Contexte et objectif. Bien que la résection trans urétrale de la prostate (RTUP) se soit imposée comme alternative à l’adénomectomie chirurgicale classique à ciel ouvert, sa pratique reste exceptionnelle dans quelques contrées africaines. L’objectif de la présente étude était de décrire la première expérience de la RTUP à Bukavu. Méthodes. La présente étude documentaire a porté sur 159 patients avec hypertrophie bénigne de la prostate (HBP), opérés dans 3 centres médicaux de Bukavu entre février 2014 et février 2017. Les paramètres d’intérêts comprenaient les données sociodémographiques, cliniques, échographiques les comorbidités, les complications et l’attitude thérapeutique avant l’intervention. Résultats. Leur âge moyen était de 68±8,5 ans. Le volume prostatique moyen était de 53,2 ± 22 grammes. Tous les patients étaient sévèrement symptomatiques (score international des symptômes prostatiques (IPSS) moyen de 26,8 ± 5,8) et fortement ennuyés (score de la qualité de vie (QOL) moyen de 6,2 ± 0,8). L’hypertension artérielle (42%) et le diabète sucré de type 2 (41 %) étaient les comorbidités les plus fréquentes. Les complications de l’HBP les plus fréquentes étaient l’infection urinaire (44 %) et la rétention urinaire (40%). Avant l’admission à l’hôpital, 60% des patients ont eu recours à la médecine traditionnelle. Conclusion. L’avènement de la RTUP à Bukavu a permis de déceler que la majorité des patients avec HBP consultent très tardivement au stade de sevérité symptomatique et des complications. Une campagne d’éducation, information et communication de la population sur le dépistage précoce de l’HBP est à envisager

Dual Averaging Method for Online Graph-structured Sparsity

Online learning algorithms update models via one sample per iteration, thus efficient to process large-scale datasets and useful to detect malicious events for social benefits, such as disease outbreak and traffic congestion on the fly. However, existing algorithms for graph-structured models focused on the offline setting and the least square loss, incapable for online setting, while methods designed for online setting cannot be directly applied to the problem of complex (usually non-convex) graph-structured sparsity model. To address these limitations, in this paper we propose a new algorithm for graph-structured sparsity constraint problems under online setting, which we call \textsc{GraphDA}. The key part in \textsc{GraphDA} is to project both averaging gradient (in dual space) and primal variables (in primal space) onto lower dimensional subspaces, thus capturing the graph-structured sparsity effectively. Furthermore, the objective functions assumed here are generally convex so as to handle different losses for online learning settings. To the best of our knowledge, \textsc{GraphDA} is the first online learning algorithm for graph-structure constrained optimization problems. To validate our method, we conduct extensive experiments on both benchmark graph and real-world graph datasets. Our experiment results show that, compared to other baseline methods, \textsc{GraphDA} not only improves classification performance, but also successfully captures graph-structured features more effectively, hence stronger interpretability.Comment: 11 pages, 14 figure

Observation of sub-Bragg diffraction of waves in crystals

We investigate the diffraction conditions and associated formation of stopgaps for waves in crystals with different Bravais lattices. We identify a prominent stopgap in high-symmetry directions that occurs at a frequency below the ubiquitous first-order Bragg condition. This sub-Bragg diffraction condition is demonstrated by reflectance spectroscopy on two-dimensional photonic crystals with a centred rectangular lattice, revealing prominent diffraction peaks for both the sub-Bragg and first-order Bragg condition. These results have implications for wave propagation in 2 of the 5 two-dimensional Bravais lattices and 7 out of 14 three-dimensional Bravais lattices, such as centred rectangular, triangular, hexagonal and body-centred cubic

Temperature-dependent trade-offs in maternal investments: An experimental test with two closely related soil microarthropods

Organisms face trade-offs in their reproductive investment due to energetic constraints. Yet, little is known about how such investments may change at different temperatures, and particularly so in soil invertebrate organisms. Here, we studied two Collembola species (Folsomia candida and Proisotoma minuta) using a long term (several generations) temperature incubation experiment (separately at 15 and 20 ◦C) to investigate how egg size and egg numbers and the trade-off between the two are affected in two temperature regimes. Both species are known to grow at these temperatures, but the variation in their reproductive strategies are little known. Our results show that egg sizes of F. candida were larger in colder temperature whereas no such patterns were found in P. minuta. By contrast, we found no effect of the two temperatures on egg numbers (per clutch) in any of the species. Moreover, we observed a negative correlation (indication of a potential trade-off) between egg size and egg numbers (per clutch) at colder temperature in F. candida, which disappeared in warmer temperature in the same species. No such trade-offs were found in P. minuta. Our results highlight that temperature effects on maternal investments are both trait- and species-specific, particularly when Collembola species are within their optimal thermal niches