The zero forcing polynomial of a graph

Zero forcing is an iterative graph coloring process, where given a set of initially colored vertices, a colored vertex with a single uncolored neighbor causes that neighbor to become colored. A zero forcing set is a set of initially colored vertices which causes the entire graph to eventually become colored. In this paper, we study the counting problem associated with zero forcing. We introduce the zero forcing polynomial of a graph $G$ of order $n$ as the polynomial $\mathcal{Z}(G;x)=\sum_{i=1}^n z(G;i) x^i$, where $z(G;i)$ is the number of zero forcing sets of $G$ of size $i$. We characterize the extremal coefficients of $\mathcal{Z}(G;x)$, derive closed form expressions for the zero forcing polynomials of several families of graphs, and explore various structural properties of $\mathcal{Z}(G;x)$, including multiplicativity, unimodality, and uniqueness.Comment: 23 page

Practical-Time Related-Key Attack on GOST with Secret S-boxes

The block cipher GOST 28147-89 was the Russian Federation encryption standard for over 20 years, and is still one of its two standard block ciphers. GOST is a 32-round Feistel construction, whose security benefits from the fact that the S-boxes used in the design are kept secret. In the last 10 years, several attacks on the full 32-round GOST were presented. However, they all assume that the S-boxes are known. When the S-boxes are secret, all published attacks either target a small number of rounds, or apply for small sets of weak keys. In this paper we present the first practical-time attack on GOST with secret S-boxes. The attack works in the related-key model and is faster than all previous attacks in this model which assume that the S-boxes are known. The complexity of the attack is less than $2^{27}$ encryptions. It was fully verified, and runs in a few seconds on a PC. The attack is based on a novel type of related-key differentials of GOST, inspired by local collisions. Our new technique may be applicable to certain GOST-based hash functions as well. To demonstrate this, we show how to find a collision on a Davies-Meyer construction based on GOST with an arbitrary initial value, in less than $2^{10}$ hash function evaluations

Calotropis procera (Apocynaceae), primeras evidencias de su naturalización en Argentina

According to observations and samples collected in northwestern Argentina, the presence of an adventitious species, Calotropis procera (Apocynaceae: Asclepiadoideae), native to Africa and SW Asia, naturalized in various parts of the world and with great invasive potential, is documented for the first time in this country. The species is described, illustrated by photographs, and information on the populations found is provided.Sobre la base de observaciones efectuadas y muestras recolectadas en el noroeste argentino, se documenta por primera vez para el país, la presencia de una especie adventicia, Calotropis procera (Apocynaceae: Asclepiadoideae) originaria de África y SO Asiático, naturalizada en diversas partes del mundo y con gran potencial invasivo. La especie es descripta, ilustrada mediante fotografías y se brinda información sobre las poblaciones halladas

Calotropis procera (Apocynaceae), first evidences of its naturalización in Argentina

Sobre la base de observaciones efectuadas y muestras recolectadas en el noroeste argentino, se documenta por primera vez para el país, la presencia de una especie adventicia, Calotropis procera (Apocynaceae: Asclepiadoideae) originaria de África y SO Asiático, naturalizada en diversas partes del mundo y con gran potencial invasivo. La especie es descripta, ilustrada mediante fotografías y se brinda información sobre las poblaciones halladas.According to observations and samples collected in northwestern Argentina, the presence of an adventitious species, Calotropis procera (Apocynaceae: Asclepiadoideae), native to Africa and SW Asia, naturalized in various parts of the world and with great invasive potential, is documented for the first time in this country. The species is described, illustrated by photographs, and information on the populations found is provided.Fil: Fabbroni, Mariela. Universidad Nacional de Salta; ArgentinaFil: Casas Marty, Ariel F.. Universidad Nacional de Salta; ArgentinaFil: Keller, Hector Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentin

The genus ruehssia (Apocynaceae) from Argentina: phylogeny, new combinations and new records

Ruehssia se restableció recientemente para clasificar a todas las especies americanas de la tribu Marsdenieae. Aquí, ofrecemos una revisión del género en la Argentina, con una clave de identificación, comentarios, un mapa de distribución e imágenes de todas las especies. La posición filogenética de todas las especies se ha evaluado utilizando secuencias de ADN nuclear y cloroplástico. Reconocemos seis especies. Además de R. altissima y R. macrophylla, incluimos dos nuevos registros, R. hilariana y R. brasiliensis, y proponemos dos nuevas combinaciones en el género, R. castillonii (Lillo ex T. Mey.) H.A. Keller & Liede y R. tressensiae (S.A. Cáceres y Morillo) H.A. Keller & Liede. Ruehssia montana y R. ulei, previamente citadas para la Argentina, no habitan en el país.Ruehssia was recently reestablished to classify all American species of the tribe Marsdenieae. Here, we provide a revision of the genus in Argentina, with an identification key, comments, a distribution map, and images of all species. The phylogenetic position of all species has been assessed using chloroplast and nuclear DNA sequences. We recognize six species. Besides R. altissima and R. macrophylla, we include two new records, R. hilariana and R. brasiliensis, and propose two new combinations in the genus, R. castillonii (Lillo ex T. Mey.) H.A. Keller & Liede and R. tressensiae (S.A. Cáceres & Morillo) H.A. Keller & Liede. Ruehssia montana and R. ulei, previously reported to Argentina, do not occur in the country.Fil: Keller, Hector Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; ArgentinaFil: Liede Schumann, Sigrid. University of Bayreuth; AlemaniaFil: Rapini, Alessandro. Universidade Estadual de Feira de Santana; BrasilFil: Caceres Moral, Sergio Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentin

Saproxylic species are linked to the amount and isolation of dead wood across spatial scales in a beech forest

ContextDead wood is a key habitat for saproxylicspecies, which are often used as indicators of habitatquality in forests. Understanding how the amount andspatial distribution of dead wood in the landscapeaffects saproxylic communities is therefore importantfor maintaining high forest biodiversity.ObjectivesWe investigated effects of the amountand isolation of dead wood on the alpha and betadiversity of four saproxylic species groups, with afocus on how the spatial scale influences results.MethodsWe inventoried saproxylic beetles, wood-inhabiting fungi, and epixylic bryophytes and lichenson 62 plots in the Sihlwald forest reserve in Switzer-land. We used GLMs to relate plot-level speciesrichness to dead wood amount and isolation on spatialscales of 20–200 m radius. Further, we used GDMs todetermine how dead wood amount and isolationaffected beta diversity.ResultsA larger amount of dead wood increasedbeetle richness on all spatial scales, while isolation hadno effect. For fungi, bryophytes and lichens this wasonly true on small spatial scales. On larger scales ofour study, dead wood amount had no effect, whilegreater isolation decreased species richness. Further,we found no strong consistent patterns explaining betadiversity