排序方式: 共有14条查询结果,搜索用时 203 毫秒
1.
Mobbs D Petrovic P Marchant JL Hassabis D Weiskopf N Seymour B Dolan RJ Frith CD 《Science (New York, N.Y.)》2007,317(5841):1079-1083
Humans, like other animals, alter their behavior depending on whether a threat is close or distant. We investigated spatial imminence of threat by developing an active avoidance paradigm in which volunteers were pursued through a maze by a virtual predator endowed with an ability to chase, capture, and inflict pain. Using functional magnetic resonance imaging, we found that as the virtual predator grew closer, brain activity shifted from the ventromedial prefrontal cortex to the periaqueductal gray. This shift showed maximal expression when a high degree of pain was anticipated. Moreover, imminence-driven periaqueductal gray activity correlated with increased subjective degree of dread and decreased confidence of escape. Our findings cast light on the neural dynamics of threat anticipation and have implications for the neurobiology of human anxiety-related disorders. 相似文献
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Carolina M. Malgarin Javier B. Zarate Predrag Novakovic Susan E. Detmer Daniel J. MacPhee John C. S. Harding 《Journal of veterinary diagnostic investigation》2021,33(2):322
Porcine reproductive and respiratory syndrome virus (PRRSV) is transmitted vertically, causing fetal death in late gestation. Spatiotemporal distribution of virus at the maternal–fetal interface (MFI) is variable, and accurate assessment of viral concentration and lesions is thus subject to sampling error. Our objectives were: 1) to assess whether viral load and lesion severity in a single sample of endometrium (END) and placenta (PLC), collected near the base of the umbilical cord (the current standard), are representative of the entire organ; and 2) to compare sampling strategies and evaluate if spatial variation in viral load can be overcome by pooling of like-tissues. Spatially distinct pieces of END and PLC of 24 fetuses from PRRSV-2–infected dams were collected. PRRSV RNA quantified by RT-qPCR was compared in 5 individual pieces per fetus and in respective pools of tissue and extracted RNA. Three distinct pieces of MFI were assessed for histologic severity. Concordance correlation and kappa inter-rater agreement were used to characterize agreement among individual samples and pools. The viral load of individual samples and pools of END had greater concordance to a referent standard than did samples of PLC. Larger pool sizes had greater concordance than smaller pool sizes. Average viral load and lesion severity did not differ by location sampled, and no technical advantages of pooling tissues versus RNA extracts were found. We conclude that multiple pieces of MFI tissues must be evaluated to accurately assess lesion severity and viral load. Three pieces per fetus provided a reasonable balance of cost and logistic feasibility. 相似文献
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Gagnon E Ranitovic P Tong XM Cocke CL Murnane MM Kapteyn HC Sandhu AS 《Science (New York, N.Y.)》2007,317(5843):1374-1378
The direct observation of molecular dynamics initiated by x-rays has been hindered to date by the lack of bright femtosecond sources of short-wavelength light. We used soft x-ray beams generated by high-harmonic upconversion of a femtosecond laser to photoionize a nitrogen molecule, creating highly excited molecular cations. A strong infrared pulse was then used to probe the ultrafast electronic and nuclear dynamics as the molecule exploded. We found that substantial fragmentation occurs through an electron-shakeup process, in which a second electron is simultaneously excited during the soft x-ray photoionization process. During fragmentation, the molecular potential seen by the electron changes rapidly from nearly spherically symmetric to a two-center molecular potential. Our approach can capture in real time and with angstrom resolution the influence of ionizing radiation on a range of molecular systems, probing dynamics that are inaccessible with the use of other techniques. 相似文献
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Both calcium (Ca2+) and silicon (Si) improve plant performance under salt (NaCl) stress. Although these two mineral elements share numerous similarities, the information on how their extracellular interactions in the root apoplast affect uptake of sodium (Na+) is still lacking. Here, we investigated the effect of high Si supply in the bioavailable form of monosilicic acid (H4SiO4) on the activity of Ca2+ in the external root solution, and subsequent root uptake and compartmentation of Na in maize (Zea mays L.). In the short‐term experiments (6 h), 14‐d‐old maize plants were exposed to various concentrations of Ca2+ at three different pH‐values (6.5, 7.5, and 8.5) and two Si concentrations, i.e., low (1 mM) and high (4 mM) supply of H4SiO4. The activity of Ca2+ and Na+ in the external solution as well as the root concentrations of total and cell sap and BaCl2‐exchangeble apoplastic fractions of both elements were analyzed. The pH of the nutrient solution affected neither the ion activities nor the root accumulation of both Ca2+ and Na+. At higher pH values (7.5 and 8.5) the interactions of Ca2+ and Si at high Si supply led to a decrease of Ca2+ activity and, hence, an increase of Na+ : Ca2+ activity ratio in the external root solution. Concomitantly, despite the elevated exchangeable apoplastic fraction of both Ca2+ and Na+, the total and cell sap concentrations were remarkably decreased for Ca2+ and increased for Na+ by the addition of 4 mM H4SiO4. This work demonstrates that at high Si supply extracellular Ca‐Si interactions leading to lowered activity of Ca2+ might rapidly compromise the ameliorative effect of Ca2+ on Na+ accumulation in roots. Practically, Si over‐fertilization of saline and, in particular, sodic soils may further promote the accumulation of Na+ in root tissues hours after Si application and, hence, increase a potential risk of Na+ toxicity. 相似文献
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Predrag Novakovic Yanyun Y. Huang Betty Lockerbie Farshid Shahriar John Kelly John R. Gordon Dorothy M. Middleton Matthew E. Loewen Beverly A. Kidney Elemir Simko 《Canadian journal of veterinary research》2015,79(2):120-128
F4ac-positive enterotoxigenic Escherichia coli (ETEC) must attach to the intestinal mucosa to cause diarrhea in piglets. Prevention of bacterial attachment to the intestinal mucosa is the most effective defense against ETEC-induced diarrhea. Porcine milk fat globule membranes (MFGM) were shown to be able to inhibit attachment of ETEC to the intestinal brush border; however, the specific components of porcine MFGM that inhibited attachment of ETEC to enterocytes were not identified. Accordingly, the purpose of this study was to identify F4ac-binding MFGM proteins by overlay Western blot and affinity chromatography. The proteome of porcine MFGM was characterized and the following F4ac-binding proteins were detected by overlay Western blot and affinity chromatography: lactadherin, butyrophilin, adipophilin, acyl-CoA synthetase 3, and fatty acid-binding protein 3. The biological function of these proteins was not investigated but it is possible that their interaction with F4ac fimbria interferes with bacterial attachment and colonization. 相似文献
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While there appear to be costs to farmers of over-applying nitrogen, there is evidence in many regions that farmers are applying nitrogen at levels that exceed those suggested by government extension services. A major reason why farmers would apparently waste money by applying more fertilizer than a crop can use is a perception that the general recommendations are not appropriate for their individual situations. In this paper we estimate the economically optimal rates for 7 Ontario sites over multiple years using four yield response functional forms to examine whether the profit-maximizing rates as determined at the end of the growing season (ex post optimal rates) are generally higher than recommended rates due to site, year, or yield response functional form differences. There was no statistical or economic basis for selecting one response model over another suggesting functional form choice or perception is not a reason for over-application. However, there was a great deal of variability found between the actual optimal rate for the season and the ex ante recommended rate, which is constant across seasons for a given site. While the recommended rate is higher than the maximum economic rate of nitrogen (MERN) on the majority of sites examined, the distribution is skewed due to a few large differences. When the recommended rate is lower than the ex post MERN in a given year, it tends to occur on less productive sites and is much lower. The pay-off function to alternative nitrogen rates is generally flat as the difference between the MERN and recommended was less than $10/ha on approximately one-third of the trials but there are large differences in the good years on less productive sites. Thus, the decision to apply more than average to take advantage of the good years is appropriate since the cost of over-application is low compared to the cost of under-application. While the pay off to soil testing for nitrogen and consequently variable rate application technology is brought into question, there appears to be significant value to information on the growing conditions for the upcoming season particularly on less productive sites. Another implication of the study is the need to have a sufficient range of application rates in nitrogen field trials for accurate estimation of the underlying response function. 相似文献
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Marina Piria Predrag Simonović Eleni Kalogianni Leonidas Vardakas Nicholas Koutsikos Davor Zanella Milica Ristovska Apostolos Apostolou Avdul Adrović Danilo Mrdak Ali Serhan Tarkan Dragana Milošević Linda N Zanella Rigers Bakiu F Güler Ekmekçi Metka Povž Kastriot Korro Vera Nikolić Rifat Škrijelj Vasil Kostov Andrej Gregori Michael K Joy 《Fish and Fisheries》2018,19(1):138-169
Fish introductions, particularly in areas of high biological diversity and endemism, represent a major threat for biodiversity. In the Balkan Peninsula, 60 fish species have been introduced to date, of which 36 have become naturalized in inland waters. Since the Balkans are one of the world's 35 biodiversity hot spots, this large presence of alien fish species poses a serious threat for the stability of freshwater ecosystems and the survival of the native ichthyofauna and of aquatic biodiversity in general. The motivation for the introductions, and the historical timeline, varies among the Balkan states. Despite recent attempts to implement and align legislation aimed at preventing the introduction of potentially invasive species, and the implementation of rigorous controls of introductions and increased protection of open waters, the majority of current introductions remain intentional, primarily via aquaculture. This review article provides a historical overview of freshwater fish introductions, the motivation behind them and the current distribution of alien freshwater fishes in the Balkans. The ecological implications and future perspectives concerning alien fish species in the region are also discussed. 相似文献
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针对当前生物质固体成型燃料抗结渣剂成本高、抗结渣效果差等实际问题,该研究采用凹土作为天然复合添加剂,制备了凹土添加量为0~7%的生物质固体成型燃料,并对其进行了工业分析及高位热值测定。燃烧生物质固体成型燃料获得灰样,采用高速相机采集灰样宏观形貌,采用扫描电镜(Scanning Electron Microscope,SEM)对灰样微观形貌进行分析。最后借助X荧光(X-ray Fluorescence,XRF)、X射线衍射(X-ray Diffraction,XRD)对生物质灰成分进行确定,以分析凹土抗结渣机理。结果表明,凹土添加量为3%以下时,热值下降速度较小,但灰分随凹土添加量增大而增加较快。由宏观形貌和微观形貌谱图发现,凹土可以极好地提升生物质固体成型燃料抗结渣性,这主要是因为添加凹土后,凹土改变了K的迁移途径,生成了更多KAlSiO4、KAlSi2O6、Ca2Mg(Si2O7)等高熔点的复盐。该研究可为解决生物质固体成型燃料行业缺乏高效低成本抗结渣剂问题提供良好解决方案。 相似文献
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Rodolphe E Gozlan Demetra Andreou Takashi Asaeda Kathleen Beyer Rachid Bouhadad Dean Burnard Nuno Caiola Predrag Cakic Vesna Djikanovic Hamid R Esmaeili Istvan Falka Duncan Golicher Akos Harka Galina Jeney Vladimír Kováč Jiří Musil Annamaria Nocita Meta Povz Nicolas Poulet Tomas Virbickas Christian Wolter A Serhan Tarkan Elena Tricarico Teodora Trichkova Hugo Verreycken Andrzej Witkowski Chun Guang Zhang Irene Zweimueller J Robert Britton 《Fish and Fisheries》2010,11(4):315-340
In recent years, policy‐makers have sought the development of appropriate tools to prevent and manage introductions of invasive species. However, these tools are not well suited for introductions of non‐target species that are unknowingly released alongside intentionally‐introduced species. The most compelling example of such invasion is arguably the topmouth gudgeon Pseudorasbora parva, a small cyprinid species originating from East Asia. A combination of sociological, economical and biological factors has fuelled their rapid invasion since the 1960s; 32 countries (from Central Asia to North Africa) have been invaded in less than 50 years. Based on a combination of monitoring surveys (2535 populations sampled) and literature reviews, this paper aims to quantify and characterise important invasion parameters, such as pathways of introduction, time between introduction and detection, lag phase and plasticity of life history traits. Every decade, five new countries have reported P. parva introduction, mainly resulting from the movement of Chinese carps for fish farming. The mean detection period after first introduction was 4 years, a duration insufficient to prevent their pan‐continental invasion. High phenotypic plasticity in fitness related traits such as growth, early maturity, fecundity, reproductive behaviour and the ability to cope with novel pathogens has predisposed P. parva to being a strong invader. The Pseudorasbora parva invasion has provided quantitative data for the development of 1) early warning systems across different spatial scales; 2) rapid eradication programmes prior to natural spread in open systems and 3) sound risk assessments with emphasis on plasticity of life history traits. 相似文献