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The pollen tube clear zone: Clues to the mechanism of polarized growth

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journal of Integrative Plant Biology 2015年第1期57卷 79-92页

作者： Peter K.Hepler lawrence j.winship Biology Department University of Massachusetts School of Natural Science Hampshire College

Pollen tubes usually exhibit a prominent region at their apex called the ＂clear zone＂ because it lacks light refracting amyloplasts. A robust, long clear zone often associates with fast growing pollen tubes, and thus serves as an indicator of pollen tube health. Nevertheless we do not understand how it arises or how it is maintained. Here we review the structure of the clear zone, and attempt to explain the factors that contribute to its formation. While amyloplasts and vacuolar elements are excluded from the clear zone, virtually all other organelles are present including secretory vesicles, mitochondria, Golgi dictyosomes, and the endoplas-mic reticulum （ER）. Secretory vesicles aggregate into an inverted cone appressed against the apical plasma membrane. ER elements move nearly to the extreme apex, whereas mitochondria and Golgi dictyosomes move less far forward. The cortical actin fringe assumes a central position in the control of clear zone formation and maintenance, given its role in generating cytoplasmic streaming. Other likely factors include the tip-focused calcium gradient, the apical pH gradient, the influx of water, and a host of signaling factors （small G-proteins）. We think that the clear zone is an emergent property that depends on the interaction of several factors crucial for polarized growth.

关键词： Actin endoplasmic reticulum myosin polarized growth pollen tube

Control of Cell Wall Extensibility during Pollen Tube Growth

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Molecular Plant 2013年第4期6卷 998-1017页

作者： Peter K. Hepler Caleb M. Rounds lawrence j. winship Biology Department University of Massachusetts Amherst MA 01003 USA School of Natural Science Hampshire College Amherst MA 01002 USA

In this review, we address the question of how the tip-growing pollen tube achieves its rapid rate of elongation while maintaining an intact cell wall. Although turgor is essential for growth to occur, the local expansion rate is controlled by local changes in the viscosity of the apical wall. We focus on several different structures and underly- ing processes that are thought to be major participants including exocytosis, the organization and activity of the actin cytoskeleton, calcium and proton physiology, and cellular energetics. We think that the actin cytoskeleton, in particular the apical cortical actin fringe, directs the flow of vesicles to the apical domain, where they fuse with the plasma mem- brane and contribute their contents to the expanding cell wall. While pH gradients, as generated by a proton-ATPase located on the plasma membrane along the side of the clear zone, may regulate rapid actin turnover and new polymeri- zation in the fringe, the tip-focused calcium gradient biases secretion towards the polar axis. The recent data showing that exocytosis of new wall material precedes and predicts the process of cell elongation provide support for the idea that the intussusception of newly secreted pectin contributes to decreases in apical wall viscosity and to cell expansion. Other prime factors will be the localization and activity of the enzyme pectin methyl-esterase, and the chelation of calcium by pectic acids. Finally, we acknowledge a role for reactive oxygen species in the control of wall viscosity.

关键词： cell expansion cell walls cytoskeleton dynamics polarity pollen development.

Oxidative Stress in Collegiate Cross Country Skiers in Mid- and Post-Seasons

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journal of Biosciences and Medicines 2024年第5期12卷 99-110页

作者： Scott P. jerome Kriya L. Dunlap Ava M. Parrish Matthew L. Lowman Emily M. Shipman lawrence K. Duffy Arleigh j. Reynolds Department of Chemistry & Biochemistry University of Alaska Fairbanks Fairbanks AK USA Institute of Arctic Biology University of Alaska Fairbanks Fairbanks AK USA Department of Biology & Wildlife University of Alaska Fairbanks Fairbanks AK USA Department of Veterinary Medicine University of Alaska Fairbanks Fairbanks AK USA

Purpose: The oxidative stress (OS) hypothesis of overtraining syndrome argues that increased production of free radicals through exercise cause muscle fatigue and damage resulting in lower athletic performance. Several studies have investigated OS immediately before and after exercise bouts in a training macrocycle. Our study aimed to compare OS of endurance athletes between a competition macrocycle and the immediate post-season recovery macrocycle. In addition, we aimed to identify athletes who experienced an unexplainable drop in athletic performance during the competition season in order to compare their OS to those who experienced no drop in performance. Methods: Fifteen members of the University of Alaska Fairbanks cross country ski team volunteered for this study. Blood samples were taken in early February (“mid-season”) and late April (“post-season”). Participants completed questionnaires regarding physical activity and athletic performance at the time of the blood draws. Plasma was analyzed for 4-hydroxynonenal (HNE), nitrotyrosine, nitric oxide (NOX), and superoxide dismutase (SOD). Significance was determined by Wilcoxon and Mann-Whitney tests. Results: Participants displayed significantly higher (p Conclusion: Signs of oxidative stress and mitigation during the post-season recovery macrocycle were higher in athletes who reported experiencing a drop in athletic performance during the competition season macrocycle.

关键词： Oxidative Stress 4-Hydroxynonenal Superoxide Dismutase Athletic Performance Training Macrocycle

NEW MURID RODENTS FROM THE LATE CENOZOIC OF YUSHE BASIN, SHANXI

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古脊椎动物学报(中英文） 1992年第1期 29-38+87-88页

作者： lawrence j.Flynn Harvard University NY Research Associate American Museum of Natural History and Peabody Museum

As scientific collaborators of the Chinese-American joint project "Neogene Rocks and Faunas, Yushe Basin, Shanxi, PRC", the present authors, with William R. Downs, Northern Arizona University, sampled the Yushe microfauna in the fall of 1987 and 1988. The fossil temains were retrieved by surface collection and by wet-sieving bulk quantities of sediment.

关键词： Yushe Basin Late cenozoic murids new taxa

Co-author Weighting in Bibliometric Methodology and Subfields of a Scientific Discipline

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journal of Data and Information Science 2020年第3期5卷 84-96页

作者： lawrence Smolinsky Aaron j Lercher Department of Mathematics Louisiana State UniversityBaton RougeLA 70803USA Middleton Library Louisiana State UniversityBaton RougeLA 70803USA

Purpose: To give a theoretical framework to measure the relative impact of bibliometric methodology on the subfields of a scientific discipline, and how that impact depends on the method of evaluation used to credit individual scientists with citations and publications. The authors include a study of the discipline of physics to illustrate the method. Indicators are introduced to measure the proportion of a credit space awarded to a subfield or a set of ***/methodology/approach: The theoretical methodology introduces the notion of credit spaces for a discipline. These quantify the total citation or publication credit accumulated by the scientists in the discipline. One can then examine how the credit is divided among the subfields. The design of the physics study uses the American Physical Society print journals to assign subdiscipline classifications to articles and gather citation, publication, and author information. Credit spaces for the collection of Physical Review journal articles are computed as a proxy for ***: There is a substantial difference in the value or impact of a specific subfield depending on the credit system employed to credit individual *** limitations: Subfield classification information is difficult to obtain. In the illustrative physics study, subfields are treated in groups designated by the Physical Review journals. While this collection of articles represents a broad part of the physics literature, it is not all the literature nor a random *** implications: The method of crediting individual scientists has consequences beyond the individual and affects the perceived impact of whole subfields and institutions. Originality/value: The article reveals the consequences of bibliometric methodology on subfields of a disciple by introducing a systematic theoretical framework for measuring the consequences.

关键词： Citation analysis Bibliometrics Research evaluation Co-author

Involvement of eicosanoids in the pathogenesis of pancreatic cancer: the roles of cyclooxygenase-2 and 5-lipoxygenase

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World journal of Gastroenterology 2014年第31期20卷 10729-10739页

作者： lawrence M Knab Paul j Grippo David j Bentrem Department of Surgery Northwestern University Feinberg School of Medicine Robert H Lurie Comprehensive Cancer Center Northwestern University jesse Brown VA Medical Center

The interplay between inflammation and cancer progression is a growing area of research. A combination of clinical, epidemiological, and basic science investigations indicate that there is a relationship between inflammatory changes in the pancreas and neoplastic progression. Diets high in ω-6 polyunsaturated fatty acids provide increased substrate for arachidonic acid metabolism by cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) to form eicosanoids. These eicosanoids directly contribute to pancreatic cancer cell proliferation. Both COX-2 and 5-LOX are upregulated in multiple cancer types, including pancreatic cancer. In vitro studies using pancreatic cancer cell lines have demonstrated upregulation of COX-2 and 5-LOX at both the mRNA and protein levels. When COX-2 and 5-LOX are blocked via a variety of mechanisms, cancer cell proliferation is abrogated both in vitro and in vivo. The mechanism of COX-2 has been shown to include effects on apoptosis as well as angiogenesis. 5-LOX has been implicated in apoptosis. The use of COX-2 and 5-LOX inhibitors in clinical studies in patients with pancreatic cancer has been limited. Patient enrollment has been restricted to those with advanced disease which makes evaluation of these drugs as chemopreventive agents difficult. COX-2 and 5-LOX expression have been shown to be present during the early neoplastic changes of pancreatic cancer, well before progression to invasive disease. This indicates that the ideal role for these interventions is early in the disease process as preventive agents, perhaps in patients with chronic pancreatitis or hereditary pancreatitis.

关键词： Arachidonic acid Eicosanoid Cyclooxygenase-2 5-lipoxygenase Pancreatic cancer Inflammation

The sky is not falling!

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Economic and Political Studies 2019年第2期7卷 122-147页

作者： lawrence j.Lau Lau Chor Tak Institute of Global Economics and Finance The Chinese University of Hong KongHong Kong SARChina

As of October 2018,almost half of US imports of goods from China are subject to new US tariffs at various rates,mostly at 10%until the year-end of 2018,when the rates were scheduled to be raised to 25%.These tariff rates will prove to be prohibitive for most if not all of the US imports from *** that US imports from China will be reduced by half,the initial direct real impact on the Chinese economy may be estimated at a loss of 0.43%of *** indirect effects are included,the full real impact may be estimated at a maximum loss of 1.12%of Chinese *** estimated impacts are relatively small and quite *** is a possibility that the scope of the US tariffs may be expanded to cover all US imports from China,in which case the full negative economic impact will be doubled,but still leaving an expected rate of economic growth in excess of 4%.The Renminbi is not likely to be significantly devalued as a result of the trade ***,there are also longer-term underlying forces at work behind the China–US trade war–the competition for economic and technological dominance and the rise of populism,isolationism,nationalism and *** is important for China–US relations,and China’s relations with the rest of the world,in particular with the European Union,Association of Southeast Asian Nations(ASEAN),japan and Russia,to be carefully managed going forward.

关键词： International trade trade war trade surplus tariff China–US relationship

Nano-enhanced solid-state hydrogen storage:Balancing discovery and pragmatism for future energy solutions

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Nano Research 2024年第10期17卷 8729-8753页

作者： Chaochao Dun Xinyi Wang Linfeng Chen Sichi Li Hanna M.Breunig jeffrey j.Urban The Molecular Foundry Lawrence Berkeley National Laboratory BerkeleyBerkeleyCA 94720USA Energy Analysis and Environmental Impacts Division Lawrence Berkeley National LaboratoryBerkeleyCA 94720USA lawrence Livermore National Laboratory LivermoreCA 94550USA

Nanomaterials have revolutionized the battery industry by enhancing energy storage capacities and charging speeds,and their application in hydrogen(H_(2))storage likewise holds strong potential,though with distinct challenges and mechanisms.H_(2) is a crucial future zero-carbon energy vector given its high gravimetric energy density,which far exceeds that of liquid ***,its low volumetric energy density in gaseous form currently requires storage under high pressure or at low *** review critically examines the current and prospective landscapes of solid-state H_(2) storage technologies,with a focus on pragmatic integration of advanced materials such as metal-organic frameworks(MOFs),magnesium-based hybrids,and novel sorbents into future energy *** materials,enhanced by nanotechnology,could significantly improve the efficiency and capacity of H_(2) storage systems by optimizing H_(2) adsorption at the nanoscale and improving the kinetics of H_(2) uptake and *** discuss various H_(2) storage mechanisms—physisorption,chemisorption,and the Kubas interaction—analyzing their impact on the energy efficiency and scalability of storage *** review also addresses the potential of“smart MOFs”,single-atom catalyst-doped metal hydrides,MXenes and entropy-driven alloys to enhance the performance and broaden the application range of H_(2) storage systems,stressing the need for innovative materials and system integration to satisfy future energy ***-throughput screening,combined with machine learning algorithms,is noted as a promising approach to identify patterns and predict the behavior of novel materials under various conditions,significantly reducing the time and cost associated with experimental *** closing,we discuss the increasing involvement of various companies in solid-state H_(2) storage,particularly in prototype vehicles,from a techno-economic *** forward-looking perspective underscores t

关键词： nanomaterials nanotechnology solid-state H_(2)storage techno-economic analysis model-driven material development processes

MAMMIFRES DE SANSAN, coordinated by Stéphane Peigné and Sevket Sen, 2012. Mémoires du Muséum National d'Histoire naturelle, Publication Scientifi que 203, 709 pages, ISBN ***ères de Sansan, key volume on a historical locality

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古脊椎动物学报 2014年第2期52卷 260-264页

作者： Dr.lawrence j.FLYNN Peabody Museum Harvard University

The Muséum National d’Histoire naturelle,via the able hands of Stéphane Peignéand Sevket Sen,has produced a massive scientific work that compiles advanced studies on the diverse mammalian fossil assemblage of Sansan,Gers,southwestern *** et al.(2012)called Sansan a"lagersttte",and so it is:a remarkable fossil site that assembles much of the biota of its past community in one *** is a site complex with

关键词：书刊内容介绍发行工作动物学