Modal Analysis and Coupling in Metal-Insulator-Metal Waveguides

This paper shows how to analyze plasmonic metal-insulator-metal waveguides using the full modal structure of these guides. The analysis applies to all frequencies, particularly including the near infrared and visible spectrum, and to a wide range of sizes, including nanometallic structures. We use the approach here specifically to analyze waveguide junctions. We show that the full modal structure of the metal-insulator-metal (MIM) waveguides--which consists of real and complex discrete eigenvalue spectra, as well as the continuous spectrum--forms a complete basis set. We provide the derivation of these modes using the techniques developed for Sturm-Liouville and generalized eigenvalue equations. We demonstrate the need to include all parts of the spectrum to have a complete set of basis vectors to describe scattering within MIM waveguides with the mode-matching technique. We numerically compare the mode-matching formulation with finite-difference frequency-domain analysis and find very good agreement between the two for modal scattering at symmetric MIM waveguide junctions. We touch upon the similarities between the underlying mathematical structure of the MIM waveguide and the PT symmetric quantum mechanical pseudo-Hermitian Hamiltonians. The rich set of modes that the MIM waveguide supports forms a canonical example against which other more complicated geometries can be compared. Our work here encompasses the microwave results, but extends also to waveguides with real metals even at infrared and optical frequencies.Comment: 17 pages, 13 figures, 2 tables, references expanded, typos fixed, figures slightly modifie

Importance of The Variations in The Origin of The PICA: Anatomical Study

Aim: Because the posterior inferior cerebellar artery (PICA) origin shows a very frequent anatomic variation, it is one of the vessels that has higher iatrogenic trauma exposure potential during surgical exposure. In this study, the aim is to investigate the variations in the origin of the PICA and stress the importance of these in terms of microsurgery. Method: This study was carried on 26 (52 hemispheres) adult cerebellum cadavers that were fixed with formalin. Red coloured latex was injected to the vertebral artery (VA ) and the PICA. The diameters of each the PICA at the origin point, the origin surface from the VA, relationship to the lower cranial nerves and other anatomic variations were investigated. Findings: PICA originated from the VA in the 46 of 47 hemispheres, in one of them it originated from BA. In five hemispheres, the PICA was absent (10.6%). In two hemispheres, the PICA (4.25%) originated from the VA's extradural segment. We found that the PICAs were wider on the left side (mean:1.50±0.42 mm on the right side, and mean:1.63±0.34 mm on the left). In eight samples ( 30.7% ) the right PICA, in twelve samples (46.3%) the left PICA was dominant. In altı samples ( 23%) both the PICAs were in equal diameter. The origin surface of the PICA from the VA was mostly posterior (36.1 %) and then lateral (31.9%) medial (23.4%) and anterior (8.4 %). The PICA left the brain stem by passing between the rootlets of the vagus nerve in the 34% of hemispheres, in the 29.8% between the rootlets of the accessory nerve, in the 25.5 % between the vagus and accessory nerves, in the 4.25% coursed rostral to the glossopharyngeal nerve, in the 2.2% between glossofaringeal and vagus nerves. Conclusions: We believe that this study is a significant research in its own field and it gives important messages in terms of knowing the anatomic variations of the PICA at origin in order to minimize surgical morbidity and mortality in the approach to the brain stem and cerebellum pathologies.Amaç: Posterior inferior serebellar arter'in (PİSA) orijini çok sık anatomik varyasyon gÖstermesi nedeniyle cerrahi yaklaşım sırasında iyatrojenik travmaya maruz kalma olasılığı fazla olan damarlardan biridir. Bu çalışmada amaç PİSA' nın orijinindeki varyasyonları incelemek ve bunların mikrocerrahi girişimler açısından Önemini vurgulamaktır. YÖntem: Bu çalışma 26 adet (52 hemisfer) formalin ile fiske edilmiş erişkin serebellum kadavrası üzerinde yapıldı. Vertebral arter (VA) ve PİSA'lara kırmızı renkli lateks injekte edildi. Her bir PİSA'nın origin noktasında kalınlıkları ve VA'den origin yüzeyi, alt kranial sinirlerle olan ilişkileri ve diğer anatomik varyasyonları incelendi. Bulgular: PİSA 47 hemisferin 46'sında VA'den, birinde BA'den origin aldı. Beş hemisferde PİSA agenetik idi (%10.6). İki hemisferde (%4.25) PİSA, VA'in ekstradural segmentinden orijin aldı. PİSA solda daha kalın bulundu. (sağda ortalama, 1.50±0.42 mm ve solda ortalama 1.63±0.34 mm). PİSA Örneklerin %30.7'sinde sağda, %46.1'inde solda dominant, %23'ünde eşit bulundu. PİSA'nın VA'den orijin yüzeyi çoğunlukla posterior (%36.1) daha sonra lateral (%31.9), medial (%23.4) ve anterior (%8.4) idi. PİSA hemisferlerin %36.1'inde vagus sinirinin rootletleri arasından, %31.9'unda aksessori sinirinin rootletleri arasından, %25.5'inde vagus ve aksessori sinirlerinin arasından, %4.25'inde glossofaringeal sinirin rostralinden ve %2.2'sinde glossofaringeal ve vagus sinirinin arasından geçerek beyin sapını terketti. Sonuçlar: Beyin sapı ve serebellum patolojilerine yaklaşımda cerrahi morbidite ve mortalitenin minimize edilmesi için PİSA'nın orijinindeki anatomik varyasyonlarının bilinmesi anlamında bu makale Önemli mesajlar vermekte ve kendi konusunda Önemli bir çalışma olduğu inancındayız

The Bosphorus Strait: Exchange fluxes, currents and sea-level changes

The flows through the Turkish Straits System (comprised of the Straits of Bosphorus and Dardanelles, and the Sea of Marmara) are subject to a great degree of transient variability, depending on the atmospheric factors and the water budget. As a result of the rapid along-strait variations in the strait geometry, the sharp stratification, and the temporary blocking of the flows in either direction, the maximal exchange regime of controlled flows in the Bosphorus exhibit complex non-linear response to forcing (by the net water budget, pressure and wind setup effects in adjacent basins), resulting in the observed time dependence from daily to interannual time scales. One consequence is the observed controls on sea level changes. Complex relationships exist between the exchange flows, sea level variations, net water budgets and atmospheric pressure variations in the adjacent basins, and are not so easily understood within the full range of time scales. We make a first attempt to discuss these relationships in some detail