Atomic-scale visualization of inertial dynamics

The motion of atoms on interatomic potential energy surfaces is fundamental to the dynamics of liquids and solids. An accelerator-based source of femtosecond x-ray pulses allowed us to follow directly atomic displacements on an optically modified energy landscape, leading eventually to the transition from crystalline solid to disordered liquid. We show that, to first order in time, the dynamics are inertial, and we place constraints on the shape and curvature of the transition-state potential energy surface. Our measurements point toward analogies between this nonequilibrium phase transition and the short-time dynamics intrinsic to equilibrium liquids.     

Geographic, terrestrial and aquatic factors: which most influence the structure of stream fish assemblages in the midwestern United States?

Abstract – Effects of environmental or landscape factors on species composition, species richness and complexity of fish assemblages were examined using our collections of fish from 65 sites on streams in 13 drainages across the midwestern United States. Effects of environmental factors were examined at three scales: broad geographic factors included drainage, latitude, and longitude; local terrestrial factors included features of the riparian zone adjacent to the collecting site as well as local climate and land use; within-stream aquatic factors related to structure and hydrology of the stream reach sampled. Each assemblage property was examined for its relationship to factors at each scale separately, and then for relative importance of all factors found to be significant in the separate analyses. Assemblage composition (summarized as sample scores on two axes of a detrended correspondence analysis) varied significantly as a function of factors at all three scales when each scale was considered separately. With simultaneous consideration of all scales, however, only broad geographic factors (particularly latitude) and local terrestrial factors explained significant variation in assemblage composition. Species richness (the number of species we captured) was explained by longitude and within-stream aquatic factors both when considered separately and together. Assemblage complexity (quantified as slope of relative abundance versus rank abundance) was only related to within-stream aquatic factors. Assemblage composition and emergent assemblage properties (richness and complexity), therefore, were explained by factors acting at different scales. The total variation explained for assemblage composition was much greater than that explained for emergent assemblage properties, suggesting that assemblage composition may vary more as a function of environmental and landscape factors than do species richness and complexity. ^NOTE     

Defining landscape-level forest types: application of latent Dirichlet allocation to species distribution models

Landscape Ecology - Forest type (FT) classification provides useful information to ecologists and forest managers by representing similar sites based on species dominance. Various methods have been...     

Determination of methyl bromide residues in stored foods using automated headspace gas chromatography

An automated gas chromatographic headspace method capable of detecting methyl bromide (MB) down to 0.01 mg kg^?1 has been developed and evaluated. The method is suitable for analysing cereals, nuts, seeds and dried fruit. Commodities are extracted with solvent and MB present is derivatised to methyl iodide (MI) which is determined by automated headspace gas chromatography. Results from the method described are compared with those using an established solvent extraction method and show good quantitative agreement. The analytical conditions recommended are likely to be suitable for examination of other commodities for MB residues.     

Effect of chromium propionate and metabolizable energy on growth,carcass traits,and pork quality of growing-finishing pigs

An experiment was conducted to evaluate the dietary effects of Cr propionate (CrProp) and metabolizable energy (ME) on growth, carcass traits, and pork quality of growing-finishing pigs. One hundred forty-four Cambrough-22 barrows were allotted to four dietary treatments in a randomized complete block design (six replicates of six pigs per replicate; average initial and final body weight were 27 and 113 kg, respectively). The dietary treatments were: 1) corn-soybean meal basal (B; low ME), 2) B + 200 ppb of Cr (as CrProp), 3) B + 200 kcal ME/kg (4.5% added fat; high ME), or 4) B + 200 kcal ME/kg + 200 ppb of Cr. At trial termination, three pigs per replicate were killed to determine dietary effects on carcass traits and pork quality. Overall average daily gain, average daily feed intake, and gain:feed ratio were not affected (P > 0.10) by diet. During the early growing period, average daily gain was increased in pigs fed the CrProp-low-ME diets, but decreased in pigs fed the CrProp-high ME diets (Cr x ME, P < 0.04). Feed intake was increased (P < 0.05) in pigs fed the high-ME diets during the early growing period. Forty-five min and 24 h pH were not affected (P > 0.10) by diet. The CIE L* tended (P = 0.07) to be increased and shear force tended (P = 0.06) to be decreased in pigs fed high-ME diets. Subjective marbling was increased (P < 0.03) and longissimus muscle percentage moisture and thaw loss were decreased (P < 0.04) in pigs fed CrProp. Chromium propionate had no consistent effect on growth and carcass traits in this experiment; however, CrProp did affect some aspects of pork quality.     

Comparisons of cultivar performance on different nutrient media in a routine method for potato micropropagation

Summary The in vitro culture of potato cultivars (Désirée, Estima, Foxton, Pentaland Squire, Record) initiated from tuber sprout buds has been studied with the requirements of a routine method of micropropagation in mind. Comparisons of the growth of the cultivars on media based on Murashige and Skoog (MS) and on Knop showed that although cultivars differed in their propensity to grow through several generations their performance on MS medium was in general superior. Sprout tips grew slower than buds from lower nodes in the first culture generation but no significant differences in growth were seen in later generations. Thus, where limited numbers of buds from lower nodes are available, sprout tips can be used to initiate cultures.

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Zusammenfassung Die aus Knospen von Knollenkeimen hervorgegangene in vitro Kultur der Kartoffelsorten Désirée, Estima, Foxton, Pentland Squire und Record wurde untersucht im Hinblick auf die Erfordernisse einer Routinemethode für eine Mikrovermehrung. Die N?hrmedien wurden wie folgt bezeichnet: M1: siehe Tab. 1; M2: wie M1, ohne Vitamine; K1: siehe Tab. 1; K2: wie K1, ohne Vitamine. Einige Sorten wuchsen schnell (Désirée, Estima), andere dagegen nur langsam (Record, Foxton) (Tab. 2). Auf dem Medium nach Murashige und Skoog (MS) was das Wachstum allgemein besser als auf dem Medium nach Knop. Einige Sorten (Désirée, Estima) wuchsen zun?chst in gleicher Weise auf beiden N?hrmedien w?hrend andere (Pentland Squire) auf MS-Medium auff?llig besser wuchsen. Unterschiede zwischen den Sorten wurden besonders deutlich, wenn die Kultur über mehrere Generationen hinweg durchgeführt wurde (Abb. 1). Désirée, Foxton und Estima zeigten w?hrend 3 Generationen einen verminderten Wuchs auf Knop's Medium, einen guten aber auf MS-Medium, w?hrmedien in gleicher Weise wuchs. Die Zugabe von Vitaminen zu den N?hrmedien beeinflusste nicht überall das Wachstum, aber in einigen F?llen zeigten einzelne Sorten eine Vorliebe für das Vorhandensein oder für das Fehlen von Vitaminen (Tab. 2). Abschnitte von Keimspitzen auf MS-Medium wuchsen zun?chst langsamer als solche aus den unteren Keimbereichen (Tab. 3), aber die Wachstumsunterschiede verschwanden in den Kulturen nach drei Generationen, so dass bei der Verwendung von Keimspitzen die Vermehrungsrate bei denjenigen Sorten erh?ht werden k?nnte, die kurze oder stark verzweigte Keime aufweisen.

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Résumé La culture in vitro de plusieurs variétés de pommes de terre (Désirée, Estima, Foxton, Pentland Squire et Record), à partir des bourgeons issus des germes de tubercule a été testée selon les recommandations d'une méthode de routine pour la micropropagation. Quatre milieux nutritifs ont été utilisés: M1=voir tabl. 1; M2=comme M1 mais sans vitamines; K1=voir tabl. 1; K2=comme K1 mais sans vitamines. Certaines variétés (Désirée, Estima) ont poussé rapidement, alors que d'autres (Record, Foxton) ont eu une croissance lente (tabl. 2). Le milieu de Murashige et Skoog (MS) a donné une croissance générale supérieure à celle de Knop. Certaines variétés (Désirée, Estima) ont eu au départ un taux de croissance similaire sur les deux types de milieu, tandis que pour d'autres (Pentland Squire) il f?t nettement plus important sur milieu MS. Les différences entre variétés sont apparues plus nettement après prolongement de la culture sur plusieurs générations (fig. 1). Désirée, Foxton et Estima ont vu leur croissance diminuer au cours de trois générations sur Knop mais non sur milieu MS, tandis que Record eut un niveau de croissance faible mais identique sur les différents milieux. L'apport de vitamines dans le milieu n'a produit aucun effet général sur la croissance, mais dans quelques cas, on notait une certaine préférence pour la présence ou l'absence des vitamines (tabl. 2). Les extrémités de germes cultivées sur milieu MS ont eu une croissance initiale plus faible que les entre-noeuds inférieurs (tabl. 3) mais les différences disparaissent après trois générations de culture, de sorte que les extrémités de germes peuvent augmenter les taux de multiplication pour les variétés à germes courts ou à forte ramification.