Planar Heterostructure Graphene -- Narrow-Gap Semiconductor -- Graphene

We investigate a planar heterostructure composed of two graphene films separated by a narrow-gap semiconductor ribbon. We show that there is no the Klein paradox when the Dirac points of the Brillouin zone of graphene are in a band gap of a narrow-gap semiconductor. There is the energy range depending on an angle of incidence, in which the above-barrier damped solution exists. Therefore, this heterostructure is a "filter" transmitting particles in a certain range of angles of incidence upon a potential barrier. We discuss the possibility of an application of this heterostructure as a "switch".Comment: 9 pages, 2 figure

Anomalies and Pathology in the Bones of the Late Cenozoic Ectothermic Tetrapods

Anomalies and pathologies can be observed in fossil animals. Among these pathologies are tumors, callus in fractures and the underdevelopment of skeleton elements. Anomalies often occur in the spine and are represented by the fusion of the vertebrae, variations in the joints and the deformation of skeletal elements.Sometimes anomalies and pathology combined in a single element of the skeleton. These anomalies and pathologies may not always be recognized in fossil material, especially if it is small in size. In this case, anomalies can be described as new taxa

Cambios de asignación genérica en especies fósiles del este de Europa descritas como Bufo belogoricus Ratnikov, 1993, Bufo planus Ratnikov, 1993 y Bufo albus Ratnikov, 1993 (Amphibia, Anura, Bufonidae)

The generic assignment of three fossil forms described as Bufo belogoricus Ratnikov, 1993, Bufo planus Ratnikov, 1993 and Bufo albus Ratnikov, 1993 is discussed. The author justifies why their original generic names should not be changed to Pseudepidalea, as recently proposed, but should be maintained until more convincing evidence is discovered.Se discute la atribución genérica de tres formas fósiles descritas como Bufo belogoricus Ratnikov, 1993, Bufo planus Ratnikov, 1993, y Bufo albus Ratnikov, 1993. El autor justifica las razones por las cuales las adscripciones genéricas originales no deberían cambiarse a Pseudepidalea, como recientemente se ha propuesto, sino mantenerse hasta que se descubra nueva evidencia más convincente