High-resolution protein structure determination by serial femtosecond crystallography     

Boutet S  Lomb L  Williams GJ  Barends TR  Aquila A  Doak RB  Weierstall U  DePonte DP  Steinbrener J  Shoeman RL  Messerschmidt M  Barty A  White TA  Kassemeyer S  Kirian RA  Seibert MM  Montanez PA  Kenney C  Herbst R  Hart P  Pines J  Haller G  Gruner SM  Philipp HT  Tate MW  Hromalik M  Koerner LJ  van Bakel N  Morse J  Ghonsalves W  Arnlund D  Bogan MJ  Caleman C  Fromme R  Hampton CY  Hunter MS  Johansson LC  Katona G  Kupitz C  Liang M  Martin AV  Nass K  Redecke L  Stellato F  Timneanu N  Wang D  Zatsepin NA  Schafer D  Defever J 《Science (New York, N.Y.)》2012,337(6092):362-364

Structure determination of proteins and other macromolecules has historically required the growth of high-quality crystals sufficiently large to diffract x-rays efficiently while withstanding radiation damage. We applied serial femtosecond crystallography (SFX) using an x-ray free-electron laser (XFEL) to obtain high-resolution structural information from microcrystals (less than 1 micrometer by 1 micrometer by 3 micrometers) of the well-characterized model protein lysozyme. The agreement with synchrotron data demonstrates the immediate relevance of SFX for analyzing the structure of the large group of difficult-to-crystallize molecules.  相似文献   

Continental-scale effects of nutrient pollution on stream ecosystem functioning     

Woodward G  Gessner MO  Giller PS  Gulis V  Hladyz S  Lecerf A  Malmqvist B  McKie BG  Tiegs SD  Cariss H  Dobson M  Elosegi A  Ferreira V  Graça MA  Fleituch T  Lacoursière JO  Nistorescu M  Pozo J  Risnoveanu G  Schindler M  Vadineanu A  Vought LB  Chauvet E 《Science (New York, N.Y.)》2012,336(6087):1438-1440

Excessive nutrient loading is a major threat to aquatic ecosystems worldwide that leads to profound changes in aquatic biodiversity and biogeochemical processes. Systematic quantitative assessment of functional ecosystem measures for river networks is, however, lacking, especially at continental scales. Here, we narrow this gap by means of a pan-European field experiment on a fundamental ecosystem process--leaf-litter breakdown--in 100 streams across a greater than 1000-fold nutrient gradient. Dramatically slowed breakdown at both extremes of the gradient indicated strong nutrient limitation in unaffected systems, potential for strong stimulation in moderately altered systems, and inhibition in highly polluted streams. This large-scale response pattern emphasizes the need to complement established structural approaches (such as water chemistry, hydrogeomorphology, and biological diversity metrics) with functional measures (such as litter-breakdown rate, whole-system metabolism, and nutrient spiraling) for assessing ecosystem health.  相似文献   

Bright coherent ultrahigh harmonics in the keV x-ray regime from mid-infrared femtosecond lasers     

Popmintchev T  Chen MC  Popmintchev D  Arpin P  Brown S  Alisauskas S  Andriukaitis G  Balciunas T  Mücke OD  Pugzlys A  Baltuska A  Shim B  Schrauth SE  Gaeta A  Hernández-García C  Plaja L  Becker A  Jaron-Becker A  Murnane MM  Kapteyn HC 《Science (New York, N.Y.)》2012,336(6086):1287-1291

High-harmonic generation (HHG) traditionally combines ~100 near-infrared laser photons to generate bright, phase-matched, extreme ultraviolet beams when the emission from many atoms adds constructively. Here, we show that by guiding a mid-infrared femtosecond laser in a high-pressure gas, ultrahigh harmonics can be generated, up to orders greater than 5000, that emerge as a bright supercontinuum that spans the entire electromagnetic spectrum from the ultraviolet to more than 1.6 kilo-electron volts, allowing, in principle, the generation of pulses as short as 2.5 attoseconds. The multiatmosphere gas pressures required for bright, phase-matched emission also support laser beam self-confinement, further enhancing the x-ray yield. Finally, the x-ray beam exhibits high spatial coherence, even though at high gas density the recolliding electrons responsible for HHG encounter other atoms during the emission process.  相似文献   

The role of driving energy and delocalized States for charge separation in organic semiconductors     

Bakulin AA  Rao A  Pavelyev VG  van Loosdrecht PH  Pshenichnikov MS  Niedzialek D  Cornil J  Beljonne D  Friend RH 《Science (New York, N.Y.)》2012,335(6074):1340-1344

The electron-hole pair created via photon absorption in organic photoconversion systems must overcome the Coulomb attraction to achieve long-range charge separation. We show that this process is facilitated through the formation of excited, delocalized band states. In our experiments on organic photovoltaic cells, these states were accessed for a short time (<1 picosecond) via infrared (IR) optical excitation of electron-hole pairs bound at the heterojunction. Atomistic modeling showed that the IR photons promote bound charge pairs to delocalized band states, similar to those formed just after singlet exciton dissociation, which indicates that such states act as the gateway for charge separation. Our results suggest that charge separation in efficient organic photoconversion systems occurs through hot-state charge delocalization rather than energy-gradient-driven intermolecular hopping.  相似文献   

Martin D?ring and Brigitte Nerlich (eds): The social and cultural impact of foot-and-mouth disease in the UK in 2001     

Paul R. Gilbert 《Agriculture and Human Values》2012,29(2):275-276

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Occurrence and molecular analysis of Campylobacter in wildlife on livestock farms     

Sippy R  Sandoval-Green CM  Sahin O  Plummer P  Fairbanks WS  Zhang Q  Blanchong JA 《Veterinary microbiology》2012,157(3-4):369-375

Wildlife harbor a variety of Campylobacter spp. and may play a significant role in the transmission of Campylobacter to livestock. Although studies have been conducted on wildlife-associated Campylobacter isolates from farms in other countries, there are little data available for livestock farms in the United States. In addition, the critical questions of whether wildlife harbor Campylobacter that is pathogenic to ruminants and/or antibiotic-resistant Campylobacter have yet to be addressed. We captured wild small mammals (n=142) and small birds (n=188) at livestock farms in central Iowa and sampled them for thermophilic Campylobacter during autumn 2009, spring 2010, and autumn 2010. Overall prevalence was 4.79%, with isolates found only in wild birds. Molecular typing revealed four multilocus sequence types (STs), three of which are novel. The remaining ST (ST-806) was found in two house sparrows and is an ST previously associated with ruminant abortion cases. Further analysis of ST-806 wild bird and ruminant abortion isolates by pulsed-field gel electrophoresis, resistance gene location, and antibiotic susceptibility tests indicated that the isolates are nearly identical. This is the first account of isolation of Campylobacter types from wild birds that are known to be pathogenic to ruminants. Furthermore, these same two wild bird isolates are resistant to the antibiotic fluoroquinolone. Our results indicate there is an overall low prevalence of Campylobacter in selected wildlife in Iowa, but suggest that wildlife may play a role in the epidemiology of pathogenic Campylobacter for domestic livestock, and may also serve as a reservoir for antibiotic-resistant Campylobacter.  相似文献   

Attributes of clinical role models as described by senior veterinary students in Australia     

Schull DN  Kyle GJ  Coleman GT  Mills PC 《Journal of veterinary medical education》2012,39(3):263-266

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Molecular epidemiology of Echinococcosis from food producing animals in north India     

Singh BB  Sharma JK  Ghatak S  Sharma R  Bal MS  Tuli A  Gill JP 《Veterinary parasitology》2012,186(3-4):503-506

Echinococcosis is an important medical, veterinary and economic concern in India. Ten cysts were randomly selected from each intermediate host species (cattle, buffalo, sheep, goat and pigs). Either the germinal layer (sterile cysts) or protoscoleces (fertile cysts) were collected for molecular characterization. A 434 base pair fragment of the mitochondrial cytochrome oxidase-1 gene was amplified using PCR from each isolate. Ten representative samples (2 from each intermediate host species) were sequenced in both the directions from which readable sequences were obtained from nine for phylogenetic analysis (NCBI, Blast). Phylogenetic analysis of cytochrome oxidase I gene revealed that seven (77.7%) isolates, from cattle (2), pigs (2), buffaloes (1) and goat (2) were clustered with the Indian Buffalo (G3) strain of Echinococcus granulosus, while two (22.2%) isolates from sheep were clustered with the sheep strain (G1) of E. granulosus. Phylogenetic analysis of the cytochrome oxidase-1 gene revealed that the buffalo strain (G3) and common sheep strain (G1) are cycling among livestock in north India and that these strains are highly adapted to cattle, buffalo, sheep, goats and pigs.  相似文献   

Effect of Restricted Grazing on Hindgut pH and Fluid Balance     

Paul D. Siciliano  Sterling Schmitt  BS 《Journal of Equine Veterinary Science》2012

Six mature idle geldings were used in a crossover design to determine the effects of restricted grazing on hindgut pH and fluid balance. Initially, horses were randomly assigned to a control group (CTRL: n = 3) having access to warm-season grass pasture continuously, or a restricted grazing (RG: n = 3) group having access to pasture for 12 consecutive hours (1900-700 hours) per 24-hour period for 7 days; they were then reassigned to the opposite treatment for an additional 7 days (i.e., CTRL: n = 6; RG: n = 6). Fecal samples were collected from each horse at 700 hours on day 7 of each period and analyzed for pH and dry matter (DM) as indicators of hindgut pH and fluid balance, respectively. Jugular blood samples were also collected at 700, 1300, and 1900 hours on day 7 and were analyzed for plasma protein as an indicator of systematic fluid balance. Fecal pH and DM data were analyzed using a paired t test. Plasma protein data were analyzed as a repeated-measures design. The mean (± SE) difference between CTRL and RG for fecal pH (.01 ± .16) and fecal DM (.68 ± .6%) was not significant (P = .93 and .52, respectively). Mean plasma protein concentrations were not affected by treatment or by treatment × sample time interaction, but tended to increase (P = .07) during the sampling period regardless of treatment. In conclusion, 12 hours of grazing restriction followed by 12 hours of grazing did not negatively impact hindgut pH or fluid balance.  相似文献   

Developments in undergraduate teaching of small-animal soft-tissue surgical skills at the University of Sydney     

Gopinath D  McGreevy PD  Zuber RM  Klupiec C  Baguley J  Barrs VR 《Journal of veterinary medical education》2012,39(1):21-29

This article discusses recent developments in soft-tissue surgery teaching at the University of Sydney, Faculty of Veterinary Science. An integrated teaching program was developed for Bachelor of Veterinary Science (BVSc) students with the aim of providing them with optimal learning opportunities to meet "Day One" small-animal soft-tissue surgical competencies. Didactic lectures and tutorials were introduced earlier into the curriculum to prepare students for live-animal surgery practical. In addition to existing clinics, additional spay/neuter clinics were established in collaboration with animal welfare organizations to increase student exposure to live-animal surgery. A silicon-based, life-like canine ovariohysterectomy model was developed with the assistance of a model-making and special effects company. The model features elastic ovarian pedicles and suspensory ligaments, which can be stretched and broken like those of an actual dog. To monitor the volume and type of student surgical experience, an E-portfolio resource was established. This resource allows for the tracking of numbers of live, student-performed desexing surgeries and incorporates competency-based assessments and reflective tasks to be completed by students. Student feedback on the integrated surgical soft-tissue teaching program was assessed. Respondents were assessed in the fourth year of the degree and will have further opportunities to develop Day One small-animal soft-tissue surgical competencies in the fifth year. Ninety-four percent of respondents agreed or strongly agreed that they were motivated to participate in all aspects of the program, while 78% agreed or strongly agreed that they received an adequate opportunity to develop their skills and confidence in ovariohysterectomy or castration procedures through the fourth-year curriculum.  相似文献