Realization and analitical and numerical analysis of a groove type resonator at millimeter waves

Bir yarı-simetrik oyuklu dalga kılavuzu rezonatörü 20 – 40 GHz frekans bandında kullanılmak üzere tasarlanmış ve duraleminyum kullanılarak gerçeklenmiştir. Rezonatör, biri düz diğeri ise dairesel oyuk içeren iki plakadan oluşmuştur. Uygun hareketli bir destek sistemine monte edilen rezonatörün, gerekli ölçüm düzeni de hazırlanarak, frekans spektrumu gözlenmiş, rezonans frekansları ve kalite faktörü ölçülmüştür. Oyuklu rezonatör, hem analitik ve hem de sayısal yöntemler kullanılarak analiz edilmiştir. Kullanılan sayısal yöntem zamanda sonlu farklar (FDTD) yöntemidir. Ölçüm sonucu elde edilen rezonans frekansları, analitik ve sayısal yöntemlerden elde edilenlerle karşılaştırılmıştır. Anahtar Kelimeler: Oyuklu dalga kılavuzu, oyuklu rezonatör, FDTD, mikrodalga, transfer rezonans metodu.As an alternative to the classical waveguides, such as the H-waveguide and the rectangular waveguide, the Groove waveguide has been used at millimeter wavelengths for the last couple of decades. It has many advantages such as low-loss and higher power handling capacity. Here, in this study, a semi-symmetrical groove guide resonator based on groove waveguide structure is designed and fabricated. Instead of using the classical symmetrical shaped groove guide, a novel semi-symmetrical groove guide structure is presented for the first time. This semi-symmetrical structure was chosen because it is easier to fabricate and excite. The groove resonator which has one grooved plate and one plane plate, first analyzed analytically. Since exact solutions usually exist for idealized geometries, the closed resonator structure is taken into account first. The Green's function method is applied for different oriented line sources. Then the transverse resonance method is used for the open groove resonator. The numerical simulations are performed via the powerful time domain simulator FDTD (Finite Difference Time Domain). Both cartesian and cylindrical coordinate systems are used for FDTD calculations. Here, the purpose to use cylindrical coordinate is to calibrate cartesian coordinates for discretization. Then, a measurement setup which includes a movable support platform was established from 20 GHz to 40 GHz. The resonance frequencies and loaded quality factor are measured. Analitical and numerical results are compared with measurements and a good agreement was observed.Keywords: Groove waveguide, groove resonator, FDTD, microwave, transverse resonance method.

A Burmese amber fossil of Radula (Porellales, Jungermanniopsida) provides insights into the Cretaceous evolution of epiphytic lineages of leafy liverworts

DNA-based divergence time estimates suggested major changes in the composition of epiphyte lineages of liverworts during the Cretaceous;however, evidence from the fossil record is scarce. We present the first Cretaceous fossil of the predominantly epiphytic leafy liverwort genus Radula in ca. 100 Myr old Burmese amber. The fossil's exquisite preservation allows first insights into the morphology of early crown group representatives of Radula occurring in gymnosperm-dominated forests. Ancestral character state reconstruction aligns the fossil with the crown group of Radula subg. Odontoradula;however, corresponding divergence time estimates using the software BEAST lead to unrealistically old age estimates. Alternatively, assignment of the fossil to the stem of subg. Odontoradula results in a stem age estimate of Radula of 227.8Ma (95% highest posterior density (HPD): 165.7-306.7) and a crown group estimate of 176.3Ma (135.1-227.4), in agreement with analyses employing standard substitution rates (stem age 235.6 Ma (142.9-368.5), crown group age 183.8 Ma (109.9-289.1)). The fossil likely belongs to the stem lineage of Radula subg. Odontoradula. The fossil's modern morphology suggests that switches from gymnosperm to angiosperm phorophytes occurred without changes in plant body plans in epiphytic liverworts. The fossil provides evidence for striking morphological homoplasy in time. Even conservative node assignments of the fossil support older rather than younger age estimates of the Radula crown group, involving origins for most extant subgenera by the end of the Cretaceous and diversification of their crown groups in the Cenozoic

Comment on the letter of the Society of Vertebrate Paleontology (SVP) dated April 21, 2020 regarding 'Fossils from conflict zones and reproducibility of fossil‑based scientific data': Myanmar amber

Recently, the Society of Vertebrate Paleontology (SVP) has sent around a letter, dated 21st April, 2020 to more than 300 palaeontological journals, signed by the President, Vice President and a former President of the society (Rayfield et al. 2020). The signatories of this letter request significant changes to the common practices in palaeontology. With our present, multi-authored comment, we aim to argue why these suggestions will not lead to improvement of both practice and ethics of palaeontological research but, conversely, hamper its further development. Although we disagree with most contents of the SVP letter, we appreciate this initiative to discuss scientific practices and the underlying ethics. Here, we consider different aspects of the suggestions by Rayfield et al. (2020) in which we see weaknesses and dangers. It is our intent to compile views from many different fields of palaeontology, as our discipline is (and should remain) pluralistic. This contribution deals with the aspects concerning Myanmar amber. Reference is made to Haug et al. (2020a) for another comment on aspects concerning amateur palaeontologists/citizen scientists/private collectors

Comment on the letter of the Society of Vertebrate Paleontology (SVP) dated April 21, 2020 regarding “Fossils from conflict zones and reproducibility of fossil‑based scientific data”: Myanmar amber

Non peer reviewe

Visible light emissions during flash sintering of 3YSZ are thermal radiation

Flash sintering enables the densification of ceramics at low furnace temperatures in a few seconds by the application of an electric field to the specimen. One of the earliest mechanisms proposed to explain the rapid densification involves the generation of Frenkel defects. Light emission during flash sintering is often interpreted as electroluminescence from electron-hole pair recombination, in support of this mechanism. In this work, experimental investigation of the emissions during flash sintering of the most widely studied ceramic, 3YSZ, shows that the visible spectrum can be explained completely in terms of black body (thermal) radiation resulting from the Joule heating of the specimen rather than electroluminescence. Apparent peaks in the spectrum are experimental artefacts associated with the equipment. There is no evidence in the visible emission spectrum during flash sintering of 3YSZ for electron-hole pair recombination associated with Frenkel pair formation or for any mechanism other than Joule heating

Optische Korngroessenbestimmung des Sohlenmaterials in Fliessgewaessern mittels Unterwasserkamera und digitaler Bildverarbeitung (UWPS) Abschlussbericht

Available from TIB Hannover: F99B919 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman