The frequency content of an earthquake ground motion is important because it affects the dynamic response of earth and structural systems. Four scalar parameters that characterize the frequency content of strong ground motions are (1) the mean period (Tm), (2) the average spectral period (Tavg), (3) the smoothed spectral predominant period (To), and (4) the predominant spectral period (Tp). Tm and Tavg distinguish the low frequency content of ground motions, while To is affected most by the high frequency content. Tp does not adequately describe the frequency content of a strong ground motion and is not recommended. Empirical relationships are developed that predict three parameters (Tm, Tavg, and To) as a function of earthquake magnitude, site-to-source distance, site conditions, and rupture directivity. The relationships are developed from a large strong-motion database that includes recorded motions from the recent earthquakes in Turkey and Taiwan. The new relationships update those previously developed by the authors and others. The results indicate that three site classes, which distinguish between rock, shallow soil, and deep soil, provide a better prediction of the frequency content parameters and smaller standard error terms than conventional “rock” and “soil” site classes. Forward directivity significantly increases the frequency content parameters, particularly Tm and To, at distances less than 20 km. Each of the frequency content parameters can be predicted with reasonable accuracy, but Tm is the preferred because it best distinguishes the frequency content of strong ground motions.

The bacterial pathogen, Xylella fastidiosa, infects many plant species in the Americas, making it a good model for investigating the genetics of host adaptation. We used multilocus sequence typing (MLST) to identify isolates of the native U.S. subsp. multiplex that were largely unaffected by intersubspecific homologous recombination (IHR) and to investigate how their evolutionary history influences plant host specialization. We identified 110 "non-IHR" isolates, 2 minimally recombinant "intermediate" ones (including the subspecific type), and 31 with extensive IHR. The non-IHR and intermediate isolates defined 23 sequence types (STs) which we used to identify 22 plant hosts (73% trees) characteristic of the subspecies. Except for almond, subsp. multiplex showed no host overlap with the introduced subspecies (subspecies fastidiosa and sandyi). MLST sequences revealed that subsp. multiplex underwent recent radiation (<25% of subspecies age) which included only limited intrasubspecific recombination (/ ‫؍‬ 0.02); only one isolated lineage (ST50 from ash) was older. A total of 20 of the STs grouped into three loose phylogenetic clusters distinguished by nonoverlapping hosts (excepting purple leaf plum): "almond," "peach," and "oak" types. These host differences were not geographical, since all three types also occurred in California. ST designation was a good indicator of host specialization. ST09, widespread in the southeastern United States, only infected oak species, and all peach isolates were ST10 (from California, Florida, and Georgia). Only ST23 had a broad host range. Hosts of related genotypes were sometimes related, but often host groupings crossed plant family or even order, suggesting that phylogenetically plastic features of hosts affect bacterial pathogenicity.T he genetic typing of bacterial isolates is an increasingly important tool for understanding the epidemiology of pathogenic bacteria. It permits us to track biogeographical patterns, host specificity, and the evolutionary changes occurring within taxa. To achieve these goals, one of the most useful and widely used typing methodologies is multilocus sequence typing (MLST), introduced in 1998 (1, 2). The spread of this methodology has been rapid in the study of human bacterial pathogens; however, MLST schemes are equally important in the study of plant pathogens (3), and schemes for plant bacteria are beginning to become established, e.g., Pseudomonas syringae (4), Xylella fastidiosa (5, 6), fruit tree phytoplasmas (7), Ralstonia solanacearum (8), Xanthomonas spp. (9), and Acidovorax citrulli (10).The genetic typing of plant pathogens provides a critical first step in answering the important question of what genetic factors determine host specificity. Genome comparison among species and pathovars of Xanthomonas suggest specificity is determined by a complex set of genetic differences involving both gene content and gene sequence (11). Of these two kinds of difference, content and sequence, gene content differences are more easily studied, since it...

The bacterium Xylella fastidiosa is a plant pathogen with a history of economically damaging introductions of subspecies to regions where its other subspecies are native. Genetic evidence is presented demonstrating the introduction of two new taxa into Central America and their introgression into the native subspecies, X. fastidiosa subsp. fastidiosa. The data are from 10 genetic outliers detected by multilocus sequence typing (MLST) of isolates from Costa Rica. Six (five from oleander, one from coffee) defined a new sequence type (ST53) that carried alleles at six of the eight loci sequenced (five of the seven MLST loci) diagnostic of the South American subspecies Xylella fastidiosa subsp. pauca which causes two economically damaging plant diseases, citrus variegated chlorosis and coffee leaf scorch. The two remaining loci of ST53 carried alleles from what appears to be a new South American form of X. fastidiosa. Four isolates, classified as X. fastidiosa subsp. fastidiosa, showed a low level of introgression of non-native DNA. One grapevine isolate showed introgression of an allele from X. fastidiosa subsp. pauca while the other three (from citrus and coffee) showed introgression of an allele with similar ancestry to the alleles of unknown origin in ST53. The presence of X. fastidiosa subsp. pauca in Central America is troubling given its disease potential, and establishes another route for the introduction of this economically damaging subspecies into the US or elsewhere, a threat potentially compounded by the presence of a previously unknown form of X. fastidiosa.

This paper examines how employer branding is used and embedded through the organizational HR practices; specifically recruitment, selection and integration. The paper adds to the growing literature on employer branding by specifically focusing upon concrete HR practices, which are often left unexplored in contemporary accounts of branding practices. Our research question is to explore the specific role that these practices play in the enactment of employer branding and assess their implications. Moreover, in order to better understand the wider significance of employer branding, scholarship needs to explore these processes in contexts where brand recognition is less prevalent. Drawing on a large multi-national organization (CollinaTrade) involved in the provision of products and services in the construction industry, the organization's minimalist focus on consumer brands makes them a useful case study for evaluating the work of employer branding outside consumer facing industries. This paper points to the significance of viewing employer branding as a management tool in terms of cultural reinforcement and symbolic representations at work and the way in which this work through HR practices. Our data shows that the logic of employer branding in contexts where the brand is less significant, is essentially contradictory, requiring both individualism and uniformity which may have a greater impact on workplace identities than previously thought.

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