How Fast are Elastic Domino Waves?

The paper is concerned with the problem of toppling propagation velocity in elastic, domino-like mechanical systems. We build on the work of Efthimiou and Johnson, who developed the theory of perfectly elastic collisions of thin rigid dominoes on a frictional foundation. This theory has been criticised for the lack of correspondence with the experimental observations, in particular, prediction of infinite propagation velocity for zero spacing between dominoes, as well as the inability to represent the collective nature of collisions in real domino systems. In our work we consider a more realistic scenario of dominoes of finite stiffness and obtain a theory of fast elastic domino waves, taking into account a limit velocity of the perturbation propagation in the system of dominoes. Moreover, finite collision time allows to extract dynamic quantities of collisions and establish upper and lower borders for domino separations where the theory could still be applied. Our discrete element simulations support our theoretical findings and shed light on the nature of collective interactions in the nearly-elastic domino chains

How Fast are Domino Waves?

The paper is concerned with the problem of toppling propagation velocity in domino-like mechanical systems. We build on the work of Efthimiou and Johnson, who developed the theory of perfectly elastic collisions of thin rigid dominoes on a frictional foundation. This theory nicely predicts important aspects of domino wave propagation, however, it leads to infinite propagation velocity for the limit of zero spacing between dominoes. In our work we account for finite stiffness of the dominoes and obtain a refined theory of fast domino waves, taking into account a limit velocity of the perturbation propagation in the system of dominoes. Moreover, finite collision time allows to extract dynamic quantities of collisions and establish upper and lower borders for domino separations where the theory is still applicable. Within the established bounds, our theory agrees with the results of real experiments and DEM numerical modeling of domino waves

Aspects of permian palaeobotany and palynology, VII. the majonicaceae, a new family of late permian conifers

On the basis of rich vegetative and fertile material from the Val Gardena Formation in the Dolomites and the Vicentinian Alps, coniferous remains have been studied in detail with the aid of cuticle analysis. Except the genus Ortiseia Florin, three other natural genera can be distinguished: Majonica nov. gen, Dolomitia nov. gen. and Pseudovoltzia Florin. Within both Majonica and Dolomitia a single species is recognized, Majonica alpina nov. sp. and Dolomitia cittertiae nov. sp., respectively. Within Pseudovoltzia two species can be recognized: P. liebeana (Geinitz) Florin and P. sjerpii nov. sp. The genera Majonica, Dolomitia and Pseudovoltzia are associated with ovuliferous fructifications and Majonica even with polliniferous cones and bisaccoid bitaeniate pollen grains. A new family—the Majonicaceae—is proposed to include the genera Majonica, Dolomitia and Pseudovoltzia. The family is characterized by a peculiar organization of the ovuliferous dwarf-shoots, i.e. the places of ovule-attachment on the lateral fertile scales varying from explicitly laterally situated to more or less shifted to the adaxial side of the dwarf-shoot

Aspects of Permian palaeobotany and palynology. IV. The conifer Ortiseia florin from the val gardena formation of the dolomites and the Vicentinian alps (Italy) with special reference to a revised concept of the Walchiaceae (Göppert) Schimper

On the basis of rich material from the Val Gardena Formation in the Dolomites and the Vicentinian Alps, the Late Permian conifer Ortiseria Florin has been studied in detail with the aid of cuticle analysis. Originally described as a form-genus for sterile remains with preserved epidermal structure, the diagnosis of Ortiseia is considerably emended by including information on the organization of the ovuliferous and polliniferous cones. Pollen grains (prepollen) correspond to the palynological form-genus Nuskoisporites Potonié et Klaus. Within Ortiseia three distinctive species can be recognized: Ortiseia leonardii Florin, Ortiseia visscheri nov. sp. and Ortiseia jonkeri nov. sp. The genus Ortiseia is compared in detail with the Late Carboniferous—Early Permian conifers Walchia Sternberg (synonym: Lebachia Florin) and Ernestiodendron Florin, especially with respect to the organization of the ovuliferous cone. There is every indication that the three genera are characterized by inverted ovules, which are abaxially attached on megasporophylls. Such a characteristic is in conflict with generally accepted reconstructions of Walchia and Ernestiodendron. Consequently, the diagnoses of these genera are emended; together with Ortiseia they are classified within the family Walchiaceae (Göppert) Schimper. Two species, formerly included in Lebachia have been transferred to Walchia: W. garnettensis (Florin) nov. comb. and W. goeppertiana (Florin) nov. comb. The form-genus Culmitzschia Ullrich is emended to include sterile walchiaceous remains with preserved epidermal structure. A number of species formerly included in Lebachia have been transferred to Culmitzschia: C. angustifolia (Florin) nov. comb., C. frondosa (Renault) nov. comb., C. hirmeri (Florin) nov. comb., C. intermedia (Florin) nov. comb., C. laxifolia (Florin) nov. comb., C. mitis (Florin) nov. comb., C. mucronata (Florin) nov. comb. and C. speciosa (Florin) nov. comb