The fragmentation criteria in local vertically stratified self-gravitating disk simulations

Massive circumstellar disks are prone to gravitational instabilities, which trigger the formation of spiral arms that can fragment into bound clumps under the right conditions. Two dimensional simulations of self-gravitating disks are useful starting points for studying fragmentation, allowing for high-resolution simulations of thin disks. However, convergence issues can arise in 2D from various sources. One of these sources is the 2D approximation of self-gravity, which exaggerates the effect of self-gravity on small scales when the potential is not smoothed to account for the assumed vertical extent of the disk. This effect is enhanced by increased resolution, resulting in fragmentation at longer cooling timescales $\beta$. If true, it suggests that the 3D simulations of disk fragmentation may not have the same convergence problem and could be used to examine the nature of fragmentation without smoothing self-gravity on scales similar to the disk scale height. To that end, we have carried out local 3D self-gravitating disk simulations with simple $\beta$ cooling with fixed background irradiation to determine if 3D is necessary to properly describe disk fragmentation. Above a resolution of $\sim 40$ grid cells per scale height, we find that our simulations converge with respect to the cooling timescale. This result converges in agreement with analytic expectations which place a fragmentation boundary at $\beta_\mathrm{crit} = 3$.Comment: 11 pages, 9 figures. Accepted for publication in Ap

Photodetection in silicon beyond the band edge with surface states

Silicon is an extremely attractive material platform for integrated optics at telecommunications wavelengths, particularly for integration with CMOS circuits. Developing detectors and electrically pumped lasers at telecom wavelengths are the two main technological hurdles before silicon can become a comprehensive platform for integrated optics. We report on the generation of free carriers in unimplanted SOI ridge waveguides, which we attribute to surface state absorption. By electrically contacting the waveguides, a photodetector with a responsivity of 36 mA/W and quantum efficiency of 2.8% is demonstrated. The photoconductive effect is shown to have minimal falloff at speeds of up to 60 Mhz

Tasmanitachoides Erwin glabellus sp. n. del norte de Queensland, Australia, con una mención sobre Tasmanitachoides lutus (Darlington) (Insecta, Coleoptera, Carabidae, Bembidiinae)

A new species of the genus Tasmanitachoides Erwin from North Queensland is described: T. glabellus n. sp. The species belongs to the T. murrumbidgensis–group of species that is characterized by its distinctly impressed clypeus, but it is distinguished from all related species by its glabrous body surface. It is the first Tasmanitachoides from northern Australia to be found in rainforest on high mountains and has thus probably preserved the original habits of the genus that are still characteristic for those species living in southern temperate regions of Australia. Tasmanitachoides lutus (Darlington) so far known from the type locality in southern New South Wales and from the holotype only, is now recorded from eastern Victoria.Se describe una nueva especie del género Tasmanitachoides Erwin del norte de Queensland: T. glabellus sp. n. Esta especie pertenece al grupo de especies T. murrumbidgensis que se caracteriza por la impresión diferenciada del clipeo, pero que se distingue de todas las especies relacionadas por presentar una superficie corporal glabra. Es el primer Tasmanitachoides del norte de Australia encontrado en la selva pluvial de alta montaña y probablemente mantiene los hábitos originales de su género, que siguen siendo característicos de las especies que viven en laszonas templadas del sur de Australia. Tasmanitachoides lutus (Darlington) conocido hasta el momento a partir de la localidad tipo, en el sur de Nueva Gales del Sur, y únicamente por el holotipo, ha sido registrado ahora en el este del estado de Victoria

Further new species of the genus Dolichoctis Schmidt-Göbel from New Guinea and surrounding islands (Insecta, Coleoptera, Carabidae, Lebiinae)

Two new species of the carabid genus Dolichoctis Schmidt-Göbel from New Guinea and New Ireland are described: D. glabripennis of the striata-group (sensu Baehr, 1999) of the nominate subgenus, from New Guinea, and D. novaeirlandiae of the subgenus Spinidolichoctis Baehr, from the island of New Ireland. In New Guinea, D. glabripennis replaces D. microdera Andrewes of the Greater Sunda Islands and Moluccas that apparently does not occur in New Guinea. D. novaeirlandiae is the first record of a Dolichoctis from this island and it is outstanding due to its very short, only dentate elytra apex

Nuevas citas del género Dolichoctis Schmidt-Göbel de Nueva Guinea e islas próximas (Insecta, Coleoptera, Carabidae, Lebiinae)

New records of species of the carabid genus Dolichoctis Schmidt–Göbel from New Guinea and several surrounding islands are dealt with. Apart from two new species that were described in another recent paper (Baehr, 2003), records of the following species from New Guinea are annotated: D. aculeata Chaudoir, D. biak Baehr, D. dentata Darlington, D. laticollis Baehr, D. striata Schmidt–Göbel, D. subquadrata Darlington, D. subrotunda Darlington, and D. suturalis Darlington. D. aculeata Chaudoir is also recorded for the first time from the island of New Britain. Additional material of D. spinipennis Chaudoir corroborates its status as a separate species, being particular for the Moluccas.Se describen nuevas citas de especies del género Dolichoctis Schmidt–Göbel (Carabidae) para Nueva Guinea y diversas islas próximas. Aparte de dos nuevas especies descritas en otro artículo reciente (Baehr, 2003), se señalan citas procedentes de Nueva Guinea para las siguientes especies: D. aculeata Chaudoir, D. biak Baehr, D. dentata Darlington, D. laticollis Baehr, D. striata Schmidt–Göbel, D. subquadrata Darlington, D. subrotunda Darlington y D. suturalis Darlington. D. aculeata Chaudoir se cita por primera vez en la isla de Nueva Bretaña. Recolecciones adicionales de D. spinipennis Chaudoir corroboran su estatus como especie separada, presente en las islas Molucas

Design of a tunable, room temperature, continuous-wave terahertz source and detector using silicon waveguides

We describe the design of a silicon-based source for radiation in the 0.5-14 THz regime. This new class of devices will permit continuously tunable, milliwatt scale, cw, room temperature operation, a substantial advance over currently available technologies. Our silicon terahertz generator consists of a silicon waveguide for near-infrared radiation, contained within a metal waveguide for terahertz radiation. A nonlinear polymer cladding permits two near-infrared lasers to mix, and through difference-frequency generation produces terahertz output. The small dimensions of the design greatly increase the optical fields, enhancing the nonlinear effect. The design can also be used to detect terahertz radiation

Trilateral tumors in four different lines of transgenic mice expressing SV40 T-antigen

Journal ArticlePURPOSE. A line of transgenic mice containing the simian virus (SV) 40 T-antigen (T-ag) gene driven by the beta-luteinizing hormone (BLH) promoter developed bilateral retinoblastoma and primitive neuroectodermal tumors (PNET) of the midbrain. Midbrain tumors arose from the subependymal layer of the cerebral aqueduct. Bilateral ocular and brain tumors ("trilateral") were found in three other SV40 T-ag transgenic murine lines containing different promoters (murine interphotoreceptor retinoid-binding protein (IRBP), human IRBP, and alpha A-crystallin). To gain insight into the regulatory mechanisms involved in central nervous system tumorigenesis, the authors examined brain tumors from four lines of SV40 T-ag mice with different promoters. METHODS. Formalin-fixed brain tumors were examined from four lines of transgenic mice containing different promoters linked to the protein coding region of the enhancerless SV40 T-ag oncogene. Transgenes contained the following promoters: BLH, mouse 1.8-kb IRBP, human 1.3-kb IRBP, and alpha A-crystallin. RESULTS. Mice with a 1.8-kb IRBP promoter develop retinal photoreceptor and pineal tumors. Intracranial tumors arising from the subependymal layer of the third ventricle also were observed. Mice with a 1.3-kb IRBP promoter exhibit bilateral retinal PNET and PNET originating from the subependymal layer of the third ventricle. Mice with the alpha A-crystallin promoter exhibit bilateral lens tumors and PNET of the midbrain. CONCLUSIONS. Ocular tumors in these mice may be ascribed to the promoter-driven, tissue-specific expression of SV40 T-ag. The common finding of PNET arising from the subependymal layer of the diencephalon is unlikely to be promoter related. These findings indicate that a regulatory region specific to the subependymal layer of the cerebral aqueduct and third ventricle resides in the structural region of the SV40 T-ag gene