共查询到20条相似文献，搜索用时 15 毫秒
1.
Boudreau BP Arnosti C Jørgensen BB Canfield DE 《Science (New York, N.Y.)》2008,319(5870):1616; author reply 1616
Rothman and Forney (Reports, 1 June 2007, p. 1325) described a model for the decay of marine organic carbon. However, the enzyme deactivation rates required by their model are too fast compared with available data, and the model fails to explain the similarity in observed decay rate constants from different experiments. Alternative models provide equally good fit to the observed temporal trend in decay rate constants. 相似文献
2.
Forces for morphogenesis investigated with laser microsurgery and quantitative modeling 总被引：1，自引：0，他引：1
Hutson MS Tokutake Y Chang MS Bloor JW Venakides S Kiehart DP Edwards GS 《Science (New York, N.Y.)》2003,300(5616):145-149
We investigated the forces that connect the genetic program of development to morphogenesis in Drosophila. We focused on dorsal closure, a powerful model system for development and wound healing. We found that the bulk of progress toward closure is driven by contractility in supracellular "purse strings" and in the amnioserosa, whereas adhesion-mediated zipping coordinates the forces produced by the purse strings and is essential only for the end stages. We applied quantitative modeling to show that these forces, generated in distinct cells, are coordinated in space and synchronized in time. Modeling of wild-type and mutant phenotypes is predictive; although closure in myospheroid mutants ultimately fails when the cell sheets rip themselves apart, our analysis indicates that beta(PS) integrin has an earlier, important role in zipping. 相似文献
3.
Humbles AA Lloyd CM McMillan SJ Friend DS Xanthou G McKenna EE Ghiran S Gerard NP Yu C Orkin SH Gerard C 《Science (New York, N.Y.)》2004,305(5691):1776-1779
Features of chronic asthma include airway hyperresponsiveness, inflammatory infiltrates, and structural changes in the airways, termed remodeling. The contribution of eosinophils, cells associated with asthma and allergy, remains to be established. We show that in mice with a total ablation of the eosinophil lineage, increases in airway hyperresponsiveness and mucus secretion were similar to those observed in wild-type mice, but eosinophil-deficient mice were significantly protected from peribronchiolar collagen deposition and increases in airway smooth muscle. These data suggest that eosinophils contribute substantially to airway remodeling but are not obligatory for allergen-induced lung dysfunction, and support an important role for eosinophil-targeted therapies in chronic asthma. 相似文献
4.
Compositional stratification in the deep mantle 总被引：2，自引：0，他引：2
A boundary between compositionally distinct regions at a depth of about 1600 kilometers may explain the seismological observations pertaining to Earth's lower mantle, produce the isotopic signatures of mid-ocean ridge basalts and oceanic island basalts, and reconcile the discrepancy between the observed heat flux and the heat production of the mid-ocean ridge basalt source region. Numerical models of thermochemical convection imply that a layer of material that is intrinsically about 4 percent more dense than the overlying mantle is dynamically stable. Because the deep layer is hot, its net density is only slightly greater than adiabatic and its surface develops substantial topography. 相似文献
5.
目的 观察金水六君煎及其拆方含药血清对肺腺癌细胞A549黏液高分泌模型黏蛋白5AC（MUC5AC）及水通道蛋白5（AQP5）表达的影响,探讨金水六君煎治疗气道黏液高分泌的作用机制。方法 将A549细胞分为空白组、模型组、金水六君煎组、养阴组、化痰组。采用人中性粒弹性蛋白酶（HNE）25 nmmol/L诱导A549细胞黏液高分泌,20%金水六君煎及其拆方含药血清干预24 h。RT-PCR、Western blot法检测细胞MUC5AC、AQP5基因与蛋白表达。ELISA法检测细胞上清液MUC5AC、AQP5蛋白表达。结果 与空白组比较,模型组细胞MUC5AC mRNA与蛋白表达明显增多（P<0.05）,AQP5 mRNA与蛋白表达明显降低（P<0.05）。与模型组比较,金水六君煎组及养阴组细胞MUC5AC mRNA表达明显降低（P<0.05）,AQP5 mRNA表达明显增多（P<0.05）;化痰组A549细胞MUC5AC蛋白表达显著降低（P<0.01）,AQP5蛋白表达明显升高（P<0.05）。模型组细胞上清液MUC5AC、AQP5蛋白表达较空白组差异无统计学意义（P>0.05）。结论 金水六君煎可明显抑制A549细胞MUC5AC产生,促进AQP5表达,纠正黏蛋白/水盐比例失衡可能是其治疗气道黏液高分泌的可能机制。 相似文献
6.
Xiao-FengMi MinTang Jin-XiangDong 《绵阳农专学报》2004,19(3):393-404
This paper proposes a virtual brush model based on droplet operation to simulate Chinese calligraph yand traditional Chinese painting in real time. Two ways of applying droplet model to virtual calligraphy and painting are discussed in detail. The second droplet model is more elaborated and can produce more vivid results while being slightly more time-consuming. The novel feature of the proposed droplet virtual brush model successfully enables the simulation painting system to overcome the poor expressional ability of virtual brush based on particle system and avoids the complex evaluation of physical brush with solid model. The model, derived from the actual calligraphy and painting experience, due to the simplicity of the droplet operation and its powerful expressive ability, considerably improves the performance of the simulation system and maintains painting effect comparable with real brush by supporting special Chinese brush effect such as dry brush, feng and stroke diffusion. 相似文献
7.
了解不同土壤生物工程措施下根系分布特征与抗拉特性对土壤生物工程措施的合理配置意义重大。以竣工5年的北京市怀柔区土壤生物工程试验区4种不同种植方式(埋根、扦插、梢捆、灌丛垫)下的金丝柳根系为研究对象,测量统计不同土层深度、不同径级的根系生物量并进行单根拉伸试验,分析在不同种植方式下金丝柳根系的生物量分布特征和单根抗拉特性,结果表明:灌丛垫和梢捆措施根系主要分布在0~40cm深度的土层中,在0~20cm土层中尤为集中。灌丛垫方式下根径≤1mm的细根含量丰富(占其总量的31.3%),须根系最为发达,梢捆次之,细根含量占其总量的19.2%。不同种植方式下根系抗拉力与直径都呈正相关,且以幂函数的规律变化。在0~20cm的土层中,不同种植方式下根系的抗拉特性存在较大差异,平均抗拉力从大到小依次为埋根、扦插、梢捆、灌丛垫;而平均延伸率从大到小依次为灌丛垫、梢捆、扦插、埋根。所以,灌丛垫和梢捆方式下根系浅层生物量较大,须根发达且具有更好的延伸性能,可有效减轻表土侵蚀,应设置在水位浮动区;埋根和扦插措施下根系能抵抗更大的剪切力,更好地深入土层深处,可设置在岸堤区。 相似文献
8.
An apical-membrane chloride channel in human tracheal epithelium 总被引：11，自引：0，他引：11
M J Welsh 《Science (New York, N.Y.)》1986,232(4758):1648-1650
The mechanism of chloride transport by airway epithelia has been of substantial interest because airway and sweat gland-duct epithelia are chloride-impermeable in cystic fibrosis. The decreased chloride permeability prevents normal secretion by the airway epithelium, thereby interfering with mucociliary clearance and contributing to the morbidity and mortality of the disease. Because chloride secretion depends on and is regulated by chloride conductance in the apical cell membrane, the patch-clamp technique was used to directly examine single-channel currents in primary cultures of human tracheal epithelium. The cells contained an anion-selective channel that was not strongly voltage-gated or regulated by calcium in cell-free patches. The channel was also blocked by analogs of carboxylic acid that decrease apical chloride conductance in intact epithelia. When attached to the cell, the channel was activated by isoproterenol, although the channel was also observed to open spontaneously. However, in some cases, the channel was only observed after the patch was excised from the cell. These results suggest that this channel is responsible for the apical chloride conductance in airway epithelia. 相似文献
9.
任雪艳 《吉林粮食高等专科学校学报》2005,20(1):34-38
阐述健康的基本概念及健康教育的重要性,结合现代高校体育教育仍存在的弊端,强调“以人为本”的思想是高校体育教学中应遵循的基本原则,从而树立“健康第一”的观念,建立强身育人,发展个性,增强终身体育意识,培养体育能力,养成自觉锻炼习惯的大学体育教育体系。 相似文献
10.
基于DPSIR模型与TOPSIS算法的吉林省土地利用系统健康诊断 总被引：3，自引：0，他引：3
土地利用系统健康评价及障碍度诊断是实现土地可持续利用和科学管理的重要基础。构建基于DPSIR框架的吉林省土地利用系统健康评价模型,TOPSIS算法结合障碍度模型对其健康状况及障碍因子进行动态综合诊断。结果表明:(1)吉林省土地利用系统健康状况呈先递减后递增的总体提升态势。(2)DPSIR子系统中,C_(驱动力)、C_(状态)、C_(影响)基本呈递增态势,C_(压力)呈现"W"型变化态势,压力较大且很不稳定,C_(响应)长期处于偏低态势。(3)准则层障碍度排序历年一致,即Y_(压力)Y_(状态)Y_(影响)Y_(驱动力)Y_(响应);指标层主要障碍因子:单位耕地面积农药施用量、全社会固定资产投资增长率、土地垦殖率、地均GDP、农民人均纯收入、农业机械化水平。引入DPSIR模型可以从系统角度看待人和环境的相互关系,将其与TOPSIS算法相结合能够客观、真实反映区域土地利用系统健康动态变化。 相似文献
11.
[目的]介绍大型犬肘头皮下黏液囊炎的诊治过程。[方法]对发病金毛犬进行初步诊断,确诊为肘头皮下黏液囊炎后对其进行手术切除。[结果]发病金毛犬的肘头皮下出现一处肿胀,其与周围有明显的分界。B超检查发现肿胀内有大面积液性暗区,外有强回声包膜。在波动稍明显的部位进行穿刺,可见有清亮黏液流出。根据初诊结果,确诊为肘头皮下黏液囊炎。手术切除该肘头皮下黏液囊后,金毛犬经精心护理后痊愈。[结论]当病情较轻时,应尽量避免切除肘头皮下粘液囊,建议应破坏黏液囊并减少其黏液的过度分泌。 相似文献
12.
Velcich A Yang W Heyer J Fragale A Nicholas C Viani S Kucherlapati R Lipkin M Yang K Augenlicht L 《Science (New York, N.Y.)》2002,295(5560):1726-1729
The gastrointestinal tract is lined by a layer of mucus comprised of highly glycosylated proteins called mucins. To evaluate the importance of mucin in intestinal carcinogenesis, we constructed mice genetically deficient in Muc2, the most abundant secreted gastrointestinal mucin. Muc2-/- mice displayed aberrant intestinal crypt morphology and altered cell maturation and migration. Most notably, the mice frequently developed adenomas in the small intestine that progressed to invasive adenocarcinoma, as well as rectal tumors. Thus, Muc2 is involved in the suppression of colorectal cancer. 相似文献
13.
杨梅癌肿病是由细菌(Pseudomonas syringnc pv.myricae)侵害引起。通过1983～1986年的试验研究表明,病菌主要潜伏在枝干的病瘤内越冬,翌年5月上旬～6月下旬,于病瘤表面溢出菌脓,经雨水传播,从伤口侵入,潜育期30～35天。经室内药效测定结果,以80％抗菌剂402乳油1000 ppm抑菌效果最佳,其次为20％叶青双可湿性粉剂400 ppm。果园药剂防治试验结果表明,对已感病的树,采取切除病瘤后用80％抗菌剂402乳油50～100倍液或20％叶青双可湿性粉剂50～100倍液涂刷伤口,均有良好的治序效果。在抽春梢前,剪除长有瘤的小谈后喷0.5％石灰倍量式波尔多液,具有保护校干、防止病害扩展蔓延的作用。 相似文献
14.
动物胃肠道中定植着数量巨大的肠道微生物,影响宿主动物的代谢和发育。肠道微生物在营养物质交换、信息传递和抵抗病原微生物入侵方面均发挥着重要的作用。依据定植部位,可以分成黏液层微生物和肠腔内微生物,Akkermansia muciniphila偏好地定植于肠道黏液层,对机体活动影响广泛。在肠道中,Akkermansia muciniphila可以特异地降解黏蛋白和低聚糖,分别产生短链脂肪酸和丙酸,在为宿主提供能量的同时也促进了自身的定植。而与此同时,机体黏蛋白的降解会促使宿主补偿产生更多的黏蛋白,进而降低宿主蛋白的沉积。Akkermansia muciniphila的定植还可减缓脂肪沉积,延缓糖尿病。在肠道微生态系统中,该菌群并没有严重的致病性,适宜丰度的Akkermansia muciniphila定植可以促进宿主免疫系统的发育,进而促进肠道健康。随着更多科学研究的展开,胃肠道微生物在机体中的重要性得到呈现。作为目前国内外的研究热点,Akkermansia muciniphila在机体肠道内的作用机制尚未完全明确。本文从Akkermansia muciniphila的定植环境、生理特性、对机体营养代谢的影响、与代谢性疾病及机体免疫相互作用等方面进行了综述,Akkermansia muciniphila为很有潜力的生物标记,应用于营养状态、代谢性疾病、免疫甚至癌症的评估和检测。 相似文献
15.
加工番茄“宽垄不翻秧”栽培模式,是一种行之有效的、全新的栽培技术。试验将“宽垄不翻秧”栽培模式与普通栽培模式在优质丰产等方面进行比较,结果表明:加工番茄“宽垄不翻秧”栽培模式在提高加工番茄的商品产量(“宽垄不翻秧”栽培模式总产量为97.74 t/hm2,传统栽培模式总产量为91.78 t/hm2,前者比后者增加6.5%),改善果实的品质(“宽垄不翻秧”栽培模式果实可溶性固形物含量为4.83%,传统栽培模式果实可溶性固形物含量为4.33%,前者比后者增加11.5%),减少烂果,增加商品果率(“宽垄不翻秧”栽培模式果实的平均商品果率、烂果率和日灼果率分别为98.21%、1.62%和0.17%;传统栽培模式果实的平均商品果率、烂果率和日灼果率分别为83.67%、15.88%和0.45%);减轻病害方面具有一定的优越性。 相似文献
16.
本文简要介绍电刷镀新技术的原理,工艺特点和应用范围。并以人造板机械“KG9”热磨机轴套应用刷镀强化和修复为例,阐述刷镀层的设计原则和主要内容,刷镀的工艺流程及其应用经济性等。 相似文献
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18.
The growth in organic and local foods consumption has been examined using two different approaches to identify characteristics and motivations of food shoppers: market segmentation and economic models using multivariate analysis. The former approach, based on Means-end Chain theory, examines how intrinsic characteristics of foods affect food choices. The latter microeconomic approach examines economic constraints and extrinsic factors. This study demonstrates value in combining the two approaches to generate better empirical predictions of who buys organic and local food. It also supports a broader theoretical framework to explain behavior in terms of intrinsic and extrinsic motivations. Using US data, an adaptation of the Food Related Lifestyle model yields four consumer lifestyles segmented by intrinsic motivations related to food. Each consumer segment exhibits distinct organic and local foods consumption behaviors. A multinomial logit model is estimated to examine the probability of being in one of these four groups as a function of extrinsic variables and economic constraints. In support of Alphabet theory and Regulatory Focus theory, we find that inclusion of extrinsic factors improves prediction of behavior and the ability to explain why they buy organic and local foods. The extrinsic variables that significantly increase the probability of being in a particular consumer food lifestyle segment include: environmental concerns, health practices, race, the presence of a farmers’ market, and to a lesser degree, family composition and income. We also find regulatory focus is most pronounced among the most active organic and local food shoppers. 相似文献
19.
Gustav Cederlöf 《Agriculture and Human Values》2016,33(4):771-784
Urban agriculture in Cuba is often promoted as an example of how agroecological farming can overcome the need for oil-derived inputs in food production. This article examines the geographical implications of Cuba’s low-carbon urban farming based on fieldwork in five organopónicos in Pinar del Río. The article charts how energy flows, biophysical relations, and socially mediated ecological processes are spatially organised to enable large-scale urban agricultural production. To explain this production system, the literature on Cuban agroecology postulates a model of two distinct modes: agroecology versus industrial agriculture. Yet this distinction inadequately explains Cuba’s urban agriculture: production in the organopónicos rather sits across categories, at once involving agroecological, organic-industrial, and petro-industrial features. To resolve this contradiction, a more nuanced framework is developed that conceptualises production systems by means of their geographical configuration. This provides analytical clarity—and a political strategy for a low-carbon, degrowth agenda. 相似文献
20.
Lee JJ Dimina D Macias MP Ochkur SI McGarry MP O'Neill KR Protheroe C Pero R Nguyen T Cormier SA Lenkiewicz E Colbert D Rinaldi L Ackerman SJ Irvin CG Lee NA 《Science (New York, N.Y.)》2004,305(5691):1773-1776
Eosinophils are often dominant inflammatory cells present in the lungs of asthma patients. Nonetheless, the role of these leukocytes remains poorly understood. We have created a transgenic line of mice (PHIL) that are specifically devoid of eosinophils, but otherwise have a full complement of hematopoietically derived cells. Allergen challenge of PHIL mice demonstrated that eosinophils were required for pulmonary mucus accumulation and the airway hyperresponsiveness associated with asthma. The development of an eosinophil-less mouse now permits an unambiguous assessment of a number of human diseases that have been linked to this granulocyte, including allergic diseases, parasite infections, and tumorigenesis. 相似文献