469 resultados para 1444


Relevância:

10.00% 10.00%

Publicador:

Resumo:

活性炭吸附蔗糖是一种化学吸附过程,蔗糖是以单分子铺展的形式被吸附于活性炭表面,其吸附速率由内扩散所控制。

Relevância:

10.00% 10.00%

Publicador:

Resumo:

螺旋藻 (Spirulina,或称节旋藻 Arthrospira) 是一类丝状不形成异型胞的蓝藻,常分布于湖泊、池塘和半咸水中。作为目前利用最广泛的经济微藻,螺旋藻的规模培养、生理生化以及分子遗传等都受到了广泛的关注。但由于缺乏足够的基因组信息,影响了螺旋藻的品种改良以及进一步的基因功能产品的开发。 本研究从挑取单藻丝开始,建立了钝顶螺旋藻 (Spirulina platensis) 的纯培养体系,并构建插入片段分别为1-2Kb和4-6Kb的基因组文库,利用鸟枪法进行全基因组测序,共得到具有8倍覆盖度的7.4Mb拼接后的基因组数据。在该草图中,预测有7795个开放读码框 (ORFs),其中包括长度小于120个氨基酸的ORFs和非全长ORFs。在所有蛋白编码序列中,约有39%的基因是螺旋藻特有的,此外,还有389个基因相对于其他蓝藻,与非蓝藻基因有着更高的相似性。通过Pfam结构域聚类分析发现,螺旋藻含有特有的结构域,如Peptidase_MA、DMT、OB、ATP-grasp、Flavokinase 等。 由于目前尚未有成熟的螺旋藻遗传转化系统,而其体内复杂的限制性内切酶系可能是妨碍外源基因顺利导入和整合的关键因素。在此草图的基础上,我们利用比较基因组学和分子进化的手段,深入分析了螺旋藻及其他蓝藻的限制修饰系统 (Restriction-modification system),为建立螺旋藻的遗传转化技术,并实现后续的螺旋藻基因功能验证模式奠定了基础。 螺旋藻及其他蓝藻的基因组计划提供了大量基因组序列和结构信息,有助于我们深入了解光合微生物基因的结构、功能和进化,以及环境因子或特定突变是如何塑造其基因组的。本文以藻胆蛋白为例,利用分子进化和群体遗传学理论,描绘出一幅藻胆蛋白进化的动态图景,并分析了环境 - 结构 - 功能之间的相互联系,为藻类捕光色素进化机制理论提供了科学依据。 本研究结果发现低光适应型原绿球藻和海洋聚球藻的藻红蛋白中正选择位点分布有着显著差异,提示二者的藻红蛋白基因有不同的进化模式;正选择作用位点多集中在藻胆蛋白的色基结合区域及XY发卡结构处,这些结构域主要与藻胆蛋白的光能捕获、能量传递和结构组装有关。该研究结果不仅揭示了正选择作用的重要性,而且提示光质、光强和能量传递压等可能是潜在的正选择压力。此外,又深入研究了高光和低光适应型两个生态群体的原绿球藻藻红蛋白基因系统发育、种内多态性和种间变异度,以此揭示环境因子对藻胆蛋白进化的影响。 本研究首次对螺旋藻全基因组进行测序,并以藻胆蛋白为例,从分子进化角度揭示其结构和功能的关系,并首次提出正选择压力可能是促使藻胆蛋白功能分化的主要原因,并认为原绿球藻中藻红蛋白的进化呈现出不同的模式,新的捕光色素的出现以及其所处的海洋环境可能使藻红蛋白获得了新的功能。

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Reported are the results of the Latin American Collaborative Study of Congenital Malformations (ECLAMC), a hospital-based case-control study of 34 293 malformed and 34 477 matched nonmalformed newborn controls. No statistical differences were found between the malformed and control groups, exposed or not exposed to tetanus toroid.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Pyrite is the most stable iron-sulfide in reduced environment, and plays an important role in geochemical iron-sulfur cycling of sediments. Thus, the presence of pyrite in sediments and rocks is an important indicator of sedimentary environments. Previous studies on the thermal products of pyrite showed that all of the products (e.g., pyrrhotite, magnetite, hematite) have strong capability of carrying remanence. To deepen our understanding of the environmental and paleomagnetic significances of pyrite, the mineral transformation processes of pyrite upon heating were systematically investigated in this study using intergrated rock magnetic experiments (in both argon and air atmospheres) and X-ray diffraction analysis. The room temperature susceptibility of the paramagnetic pyrite is about 2.68×10-5 SI. In argon atmosphere (reducing environment), pyrite was transformed into monoclinic stable single domain (SD) pyrrhotite above 440 C. The corresponding coercive force and remanence coercivity are about 20 mT and 30 mT, respectively. In contrast, in air atmosphere (oxidation environment), the intermediate thermal products of pyrite are magnetite and pyrrhotite, which were quickly further oxidated to SD hematite, which has coercivity of about 1400 mT. In addition, the hematite particles gradually grow from SD to PSD grain size region by multiple heating runs. The transformation processes of pyrite in oxidation atomosphere can be interpreted by three possible pathways: (1) pyrite→magnetite→hematite; (2) pyrite→pyrrhotite→magnetite→hematite; and (3) pyrite→pyrrhotite→hematite. Low-temperature magnetic experiments show no transitions for pyrite. Despite that low-temperature magnetic method is not suitable for identification of pyrite, it is clear in this study that the high-temperature thermomagnetic measurements (e.g.,  -T and J-T curves) are very sensitive to the presence of pyrite in sediments and rocks. Nevertheless, for the thermal treatment products, low-temperature magnetic measurements showed the 34 K transition of pyrrhotite and the 250 K Morine transition of hematite. Iron-sulfide has also been found on Martian meteorolites by other workers. Therefore, systematic study of rock magnetism of pyrite (and other iron-sulfides) and their products will have great significances for both paleomagnetism and planetary magnetism.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

This thesis describes a system that synthesizes regularity exposing attributes from large protein databases. After processing primary and secondary structure data, this system discovers an amino acid representation that captures what are thought to be the three most important amino acid characteristics (size, charge, and hydrophobicity) for tertiary structure prediction. A neural network trained using this 16 bit representation achieves a performance accuracy on the secondary structure prediction problem that is comparable to the one achieved by a neural network trained using the standard 24 bit amino acid representation. In addition, the thesis describes bounds on secondary structure prediction accuracy, derived using an optimal learning algorithm and the probably approximately correct (PAC) model.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Książka stanowi plon 2-letniego projektu badawczego zrealizowanego na Wydziale Neofilologii UAM przez zespół złożony z psychologa i filologów aż czterech specjalności językowych. Prezentuje zagadnienia ogólne (m.in. specyfilę komunikacji ustnej, kształtowanie postaw proautonomicznych i osobistej kompetencji komunikacyjnej) oraz sprawozdania z badań (dotyczące m.in. kształtowania samooceny, wrażliwości językowej, umiejętności argumentacyjnych i postawy podmiotowej).

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Publikacja zawiera wybór 14 artykułów zaprezentowanych w trakcie sympozjum nt. „Autonomizacja studentów a efektywność dydaktyki na poziomie zaawansowanym”, które odbyło się w dn. 4-5 lutego 2002 roku w Uniwersytecie im. Adama Mickiewicza w Poznaniu na zakończenie projektu badawczego pod tym samym tytułem. Autorów łączy innowacyjność podejścia, ukierunkowana na autonomizację studentów. Artykuły obejmują następujące grupy zagadnień: opis stosowanych procedur dydaktycznych, badania i obserwacje efektów tych innowacji, a także wybrane ujęcia teoretyczne. Zbiór stanowi reprezentatywny przegląd aktualnej refleksji i stanu badań empirycznych w szeroko pojętym ujęciu autonomizacyjnym.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

Jak efektywnie doskonalić się w komunikacji ustnej na poziomie zaawansowanym? Publikacja niniejsza podejmuje tę kwestię w sposób całościowy i nowatorski, sytuując ją w perspektywie autonomizacji. Jest to plon 2-letniego projektu badawczego zrealizowanego na Wydziale Neofilologii UAM przez zespół pod kierunkiem prof. W. Wilczyńskiej, złożony z psychologa i 10 filologów aż 5 specjalności językowych. Część I obejmuje zagadnienia ogólne: specyfikę komunikacji ustnej, kształtowanie postaw proautonomicznych i osobistej kompetencji komunikacyjnej, relację współpracy dydaktycznej, zastosowaną metodologię badań, implikacje dydaktyczne. Część II zawiera 9 szczegółowych sprawozdań z badań dotyczących m.in. kształtowania samooceny, wrażliwości językowej, umiejętności argumentacyjnych i postawy podmiotowej. Całość uzupełnia słowniczek terminów dotyczących autonomizacji oraz bibliografia. W sumie praca ta stanowi dobre wprowadzenie do badań glottodydaktycznych, a także autorską i pogłębioną refleksję nad wybraną problematyką.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

John Templeton Foundation

Relevância:

10.00% 10.00%

Publicador:

Resumo:

This work employs a custom built body area network of wireless inertial measurement technology to conduct a biomechanical analysis of precision targeted throwing in competitive and recreational darts. The solution is shown to be capable of measuring key biomechanical factors including speed, acceleration and timing. These parameters are subsequently correlated with scoring performance to determine the affect each variable has on outcome. For validation purposes an optical 3D motion capture system provides a complete kinematic model of the subject and enables concurrent benchmarking of the 'gold standard' optical inertial measurement system with the more affordable and proactive wireless inertial measurement solution developed as part of this work.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

OBJECTIVES: To assess the performance of WHO's "Guidelines for care at the first-referral level in developing countries" in an area of intense malaria transmission and identify bacterial infections in children with and without malaria. DESIGN: Prospective study. SETTING: District hospital in Muheza, northeast Tanzania. PARTICIPANTS: Children aged 2 months to 13 years admitted to hospital for febrile illness. MAIN OUTCOME MEASURES: Sensitivity and specificity of WHO guidelines in diagnosing invasive bacterial disease; susceptibility of isolated organisms to recommended antimicrobials. RESULTS: Over one year, 3639 children were enrolled and 184 (5.1%) died; 2195 (60.3%) were blood slide positive for Plasmodium falciparum, 341 (9.4%) had invasive bacterial disease, and 142 (3.9%) were seropositive for HIV. The prevalence of invasive bacterial disease was lower in slide positive children (100/2195, 4.6%) than in slide negative children (241/1444, 16.7%). Non-typhi Salmonella was the most frequently isolated organism (52/100 (52%) of organisms in slide positive children and 108/241 (45%) in slide negative children). Mortality among children with invasive bacterial disease was significantly higher (58/341, 17%) than in children without invasive bacterial disease (126/3298, 3.8%) (P<0.001), and this was true regardless of the presence of P falciparum parasitaemia. The sensitivity and specificity of WHO criteria in identifying invasive bacterial disease in slide positive children were 60.0% (95% confidence interval 58.0% to 62.1%) and 53.5% (51.4% to 55.6%), compared with 70.5% (68.2% to 72.9%) and 48.1% (45.6% to 50.7%) in slide negative children. In children with WHO criteria for invasive bacterial disease, only 99/211(47%) of isolated organisms were susceptible to the first recommended antimicrobial agent. CONCLUSIONS: In an area exposed to high transmission of malaria, current WHO guidelines failed to identify almost a third of children with invasive bacterial disease, and more than half of the organisms isolated were not susceptible to currently recommended antimicrobials. Improved diagnosis and treatment of invasive bacterial disease are needed to reduce childhood mortality.

Relevância:

10.00% 10.00%

Publicador:

Resumo:

The end products of atmospheric degradation are not only CO2 and H2O but also sulfate and nitrate depending on the chemical composition of the substances which are subject to degradation processes. Atmospheric degradation has thus a direct influence on the radiative balance of the earth not only due to formation of greenhouse gases but also of aerosols. Aerosols of a diameter of 0.1 to 2 micrometer, reflect short wave sunlight very efficiently leading to a radiative forcing which is estimated to be about -0.8 watt per m2 by IPCC. Aerosols also influence the radiative balance by way of cloud formation. If more aerosols are present, clouds are formed with more and smaller droplets and these clouds have a higher albedo and are more stable compared to clouds with larger droplets. Not only sulfate, but also nitrate and polar organic compounds, formed as intermediates in degradation processes, contribute to this direct and indirect aerosol effect. Estimates for the Netherlands indicate a direct effect of -4 watt m-2 and an indirect effect of as large as -5 watt m-2. About one third is caused by sulfates, one third by nitrates and last third by polar organic compounds. This large radiative forcing is obviously non-uniform and depends on local conditions.