Superconducting-coil--resistor circuit with electric field quadratic in the current

It is shown for the first time that the observed [Phys. Lett. A 162 (1992) 105] potential difference Phi_t between the resistor and the screen surrounding the circuit is caused by polarization of the resistor because of the kinetic energy of the electrons of the superconducting coil. The proportionality of Phi_t to the square of the current and to the length of the superconducting wire is explained. It is pointed out that measuring Phi_t makes it possible to determine the Fermi quasimomentum of the electrons of a metal resistor.Comment: 2 pages, 1 figur

Stand Up for Petrograd! (грудью на защиту петрограда!)

Propaganda poster exhorting workers and soldiers to defend the city of Petrograd (St. Petersburg) against counter-revolutionary forces in the civil war that erupted after the Russian Revolution.https://digitalcommons.risd.edu/picturecollection_russianposters/1001/thumbnail.jp

Genetic diversity in the endangered tropical tree, Guaiacum sanctum (Zygophyllaceae)

Fragmentation of tropical forests has changed continuous tropical landscapes into a network of poorly connected fragments, reducing population sizes and potentially increasing genetic isolation. This study quantifies genetic diversity within and among the 7 extant populations of the endangered tropical tree Guaiacum sanctum in Costa Rica. We describe how genetic diversity differs between populations representing continuous and fragmented habitats. Allozyme analyses were conducted on adult samples from populations representing 2 geographic regions in northwestern Costa Rica. We found high levels of genetic diversity within the species (Hes = 0.329) and significant but relatively small differences in allele frequencies among populations (GST = 0.101) and between regions (GST = 0.053). We found no differences in genetic diversity between fragmented and continuous populations. Evidence for significant isolation-by-distance (IBD) was seen only when all populations were analyzed. If populations within the 2 regions were analyzed separately, IBD ceased to be significant. Our results suggest that the patterns of genetic diversity observed for G. sanctum may be caused by the ancient separation of populations into 2 disjunct geographic regions with extensive historical rates of gene flow among populations within each region. Recent forest fragmentation has not yet affected patterns of genetic diversity in this species.Idea WildUniversidad de Costa RicaOrganization for Tropical StudiesNational Science FoundationUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí