287 resultados para PL-100
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凋落物的分解对生物地球化学循环起着重要的作用。本研究以位于中国北方农牧交错区(内蒙古多伦县)的半干旱克氏针茅(Stipa krylovii Roshev.)草原生态系统为背景,针对凋落物分解研究中的几个关键过程和问题进行了探讨。研究内容包括该生态系统中几种常见植物凋落物的分解速率,在分解过程中的养分动态,凋落物的混合效应(即非加性效应)及其机制,全球变化引起的土壤有效N、P和降水增加对凋落物分解的影响及其对草原生态系统碳储量的影响等。 通过对克氏针茅、糙隐子草(Cleistogenes squarrosa Trin.)、双齿葱(Allium bidentatum Fisch.)、野韭(Allium ramosum L. Sp. Pl.)和冰草(Agropyron cristatum Gaertn.)的叶、茎、根凋落物的研究发现,叶和茎的分解速率与凋落物初始N和P含量呈显著正相关,根系的分解速率与初始C/N比呈显著负相关。根系凋落物一般比叶和茎凋落物分解速率快,而且具有更快的养分周转速率。有些凋落物混合在一起分解后对分解速率产生了混合效应(混合凋落物的实际分解速率偏离于基于组分凋落物计算的预期分解速率),同时它们对养分(主要是N、P、Ca、Mg)的固定或释放被延后。混合效应发生与否以及混合效应的方向主要取决于组分凋落物的特点,而与凋落物多样性的高低没有明显的关系。混合凋落物对养分动态的负作用,能降低退化生态系统遭到干扰后养分的损失,而且养分释放时间的延后有助于某些植物更好地生长,有利于退化草原生态系统恢复过程中植被结构的改善。 由于凋落物的质量对分解速率的影响重大,凋落物的化学组成很可能对混合凋落物分解过程中的非加性效应起重要作用,然而迄今为止没有明确的结论。本文研究发现,具有不同初始N、P含量的凋落物(同一物种)混合在一起分解后产生了正的非加性效应,非加性效应的强弱与组分凋落物初始N、P含量的差异大小有关。而且,非加性效应与P含量差异大小的相关性比与N的强,这可能与研究地点土壤中P的含量相对更为缺乏有关。这一研究结果表明,凋落物的化学组成在有些情况下确实与非加性效应有关。 通过施肥和浇水试验,研究了全球变化引起的土壤有效N、P和水分的增加对具有不同生活型和化学组成的两种优势草原植物,即双齿葱和克氏针茅凋落物分解的直接影响。结果发现,向土壤中添加N肥或N、P复合肥,在短期内(100天)加速了这两种植物的分解速率。高质量凋落物(双齿葱)的分解更容易受到土壤水分条件的限制,而低质量凋落物(克氏针茅)的分解对土壤养分有效性更敏感。土壤中有效养分的增加会提高分解凋落物对养分的固定,有利于退化生态系统中养分的保持。双齿葱对内蒙古半干旱典型草原的碳循环和养分动态的贡献,比克氏针茅要更大。研究结果提示人们,对草原生态系统的碳循环和养分动态进行模拟时,需要对不同化学组成的凋落物分别加以考虑。 本文还探讨了土壤有效N长期增加后对两种优势草原植物(克氏针茅和冷蒿(Artemisia frigida Willd))凋落物分解的综合影响,并进一步区分了由土壤有效N增加引起的凋落物质量改变的间接作用和土壤状况改变的直接作用。结果发现,土壤有效N长期增加后对凋落物的分解速率没有明显影响,但是显著加速了分解凋落物对养分的固定,这可能是由于凋落物质量对分解的促进作用和土壤状况对分解的抑制作用相互抵消的原因所造成的。向土壤中添加N素后,地上部植被生产力不可避免的会提高,尽管短期内会加速凋落物的分解速率,但从长远来看,对凋落物的分解速率不会产生影响,所以估计土壤有效N增加后最终会提高草原生态系统的净碳储量。 通过本研究,对中国北方农牧交错区(内蒙古多伦县)半干旱克氏针茅草原生态系统的养分循环过程有了初步的了解,验证了混合凋落物分解过程中非加性效应发生的可能性,并且证明组分凋落物的初始化学组成对这种非加性效应确实起着重要作用。本研究说明全球变化对不同植物种凋落物分解的影响是不同的,而且因研究时间长短的不同对凋落物分解的影响会发生变化。研究结果为草原生态系统碳和养分循环过程的模拟提供了必要的基础资料,为混合凋落物分解过程中非加性效应发生的可能机制提供了强有力的证据,对在全球变化背景下人们对草原生态系统碳和养分循环过程的认识和模拟有着重要的参考价值。
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The Afrotheria, a supraordinal grouping of mammals whose radiation is rooted in Africa, is strongly supported by DNA sequence data but not by their disparate anatomical features. We have used flow-sorted human, aardvark, and African elephant chromosome painting probes and applied reciprocal painting schemes to representatives of two of the Afrotherian orders, the Tubulidentata (aardvark) and Proboscidea (elephants), in an attempt to shed additional light on the evolutionary affinities of this enigmatic group of mammals. Although we have not yet found any unique cytogenetic signatures that support the monophyly of the Afrotheria, embedded within the aardvark genome we find the strongest evidence yet of a mammalian ancestral karyotype comprising 2n = 44. This karyotype includes nine chromosomes that show complete conserved synteny to those of man, six that show conservation as single chromosome arms or blocks in the human karyotype but that occur on two different chromosomes in the ancestor, and seven neighbor-joining combinations (i.e., the synteny is maintained in the majority of species of the orders studied so far, but which corresponds to two chromosomes in humans). The comparative chromosome maps presented between human and these Afrotherian species provide further insight into mammalian genome organization and comparative genomic data for the Afrotheria, one of the four major evolutionary clades postulated for the Eutheria.
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Penaeus monodon postlarvae were fed with different percentages (0%, 25%, 50%, 75% and 100%) of the herbal appetizer Zingiber officinalis enriched Artemia. After 30 days of culture (i.e. PL-1-30), a very positive result was found in Z. officinalis-enriched Artemia-fed postlarvae. The unenriched Artemia-fed postlarvae consumed 91.0 mg/animal/30 days of feed, whereas the Z. officinalis-enriched Artemia increased their consumption to 127.9 mg/animal/30 days. A similar pattern was noticed in feed absorbed (110.2 mg), dry weight growth (26.7 mg) and feed catabolized (83.2 mg) in Z. officinalis-enriched Artemia because of enzymatic activities. The conversion efficiency of unenriched postlarva was 17.19%, whereas in 100% Z. officinalis-enriched Artemia, the maximum conversion efficiency was 20.85%. The net production efficiency increased significantly (P < 0.05) to 22% from that of the unenriched Artemia-fed postlarvae. The administration of Z. officinalis in all levels produced significantly (P < 0.05) higher weight gain and specific growth rate. The utilization efficiency of feed increased proportionately to the percentages of Z. officinalis. Digestive enzyme activity (amylase, protease and lipase) increased significantly (P < 0.05) in the 50%, 75% and 100% enrichment. Among the different percentages of enrichment, the 100% Z. officinalis-enriched Artemia-fed postlarvae performed better in the overall status.
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Submitted by zhangdi (zhangdi@red.semi.ac.cn) on 2009-06-04T08:36:34Z No. of bitstreams: 1 dspace.cfg: 33388 bytes, checksum: ac9630d3fdb36a155287a049e8b34eb7 (MD5)
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A flat, fully strain-relaxed Si0.72Ge0.28 thin film was grown on Si (1 0 0) substrate with a combination of thin low-temperature (LT) Ge and LT-Si0.72Ge0.28 buffer layers by ultrahigh vacuum chemical vapor deposition. The strain relaxation ratio in the Si0.72Ge0.28 film was enhanced up to 99% with the assistance of three-dimensional Ge islands and point defects introduced in the layers, which furthermore facilitated an ultra-low threading dislocation density of 5 x 10(4) cm (2) for the top SiGe film. More interestingly, no cross-hatch pattern was observed on the SiGe surface and the surface root-mean-square roughness was less than 2 nm. The temperature for the growth of LT-Ge layer was optimized to be 300 degrees C. (C) 2008 Elsevier B.V. All rights reserved.
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We have studied the lateral carrier transfer in a specially designed quantum dot chain structure by means of time-resolved photoluminescence (PL) and polarization PL. The PL decay time increases with temperature, following the T-1/2 law for the typical one-dimensional quantum system. The decay time depends strongly on the emission energy: it decreases as the photon energy increases. Moreover, a strong polarization anisotropy is observed. These results are attributed to the efficient lateral transfer of carriers along the chain direction. (c) 2008 American Institute of Physics.
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Hexagonal nanopillars with a single InGaAs/GaAs quantum well (QW) were fabricated on a GaAs (111) B substrate by selective-area metal-organic vapor phase epitaxy. The standard deviations in diameter and height of the nanopillars are about 2% and 5%, respectively. Zincblende structure and rotation twins were identified in both the GaAs and the InGaAs layers by electron diffraction. The excitation-power-density-dependent micro-photoluminescence (mu-PL) of the nanopillars was measured at 4.2, 50, 100 and 150 K. It was shown that, with increasing excitation power density, the mu-PL peak's positions shift to a higher energy, and their intensity and width increase, which were rationalized using a model that includes the effects of piezoelectricity, photon-screening and band-filling. It was also revealed that the rotation twins significantly reduce the diffusion length of the carriers in the nanopillars, compared to that in the regular semiconductors.
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High-quality Ge epilayer on Si(1 0 0) substrate with an inserted low-temperature Ge seed layer and a thin Si0.77Ge0.23 layer was grown by ultrahigh vacuum chemical vapor deposition. The epitaxial Ge layer with surface root-mean-square roughness of 0.7 nm and threading dislocation density of 5 x 10(5) cm(-2) was obtained. The influence of low temperature Ge seed layer on the quality of Ge epilayer was investigated. We demonstrated that the relatively higher temperature (350 degrees C) for the growth of Ge seed layer significantly improved the crystal quality and the Hall hole mobility of the Ge epilayer. (C) 2008 Elsevier B.V. All rights reserved.
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The formation process of InAs quantum dots (QDs) on vicinal GaAs (1 0 0) substrates is studied by atomic force microscopy (AFM). It is found that after 1.2 MLs of InAs deposition, while the QDs with diameters less than the width of the multi-atomic steps are shrinking, the larger QDs are growing. Photoluminescence measurements of the uncapped QDs correspond well to the AFM structure observations of the QDs. We propose that the QDs undergo an anomalous coarsening process with modified growth kinetics resulting from the restrictions of the finite terrace sizes. A comparison between the QDs on the vicinal GaAs (1 0 0) substrates and the QDs on the exact GaAs (1 0 0) further verifies the effect of the multi-atomic steps on the formation of QDs.
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The GaN-rich side of GaNP ternary alloys has been successfully synthesized by light-radiation heating and low-pressure metal-organic chemical vapor deposition. X-ray diffraction (XRD) rocking curves show that the ( 0002) peak of GaNP shifts to a smaller angle with increasing P content. From the GaNP photoluminescence (PL) spectra, the red shifts from the band-edge emission of GaN are determined to be 73, 78 and 100 meV, respectively, in the GaNP alloys with the P contents of 1.5%, 5.5% and 7.5%. No PL peak or XRD peak related to GaP is observed, indicating that phase separation induced by the short-range distribution of GaP-rich regions in the GaNP layer has been effectively suppressed. The phase-separation suppression in the GaNP layer is associated with the high growth rate and the quick cooling rate under the given growth conditions, which can efficiently restrain the accumulation of P atoms in the GaNP layer.
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Gadolinium oxide thin films have been prepared on silicon (100) substrates with a low-energy dual ion-beam epitaxial technique. Substrate temperature was an important factor to affect the crystal structures and textures in an ion energy range of 100-500 eV. The films had a monoclinic Gd2O3 structure with preferred orientation ((4) over bar 02) at low substrate temperatures. When the substrate temperature was increased, the orientation turned to (202), and finally, the cubic structure appeared at the substrate temperature of 700 degreesC, which disagreed with the previous report because of the ion energy. The AES studies found that Gadolinium oxide shared Gd2O3 structures, although there were a lot of oxygen deficiencies in the films, and the XPS results confirmed this. AFM was also used to investigate the surface images of the samples. Finally, the electrical properties were presented. (C) 2004 Elsevier B.V. All rights reserved.
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Semiconductor equilateral triangle microresonators (ETRs) with side length of 5, 10, and 20 mum are fabricated by the two-step inductively coupled plasma (ICP) etching technique. The mode properties of fabricated InGaAsP ETRs are investigated experimentally by photoluminescence (PL) with the pumping source of a 980-nm semiconductor laser and distinct peaks are observed in the measured PL spectra. The wavelength spacings of the distinct peaks agree very well with the theoretical longitudinal mode intervals of the fundamental transverse modes in the ETRs, which verifies that the distinct peaks are corresponding to the enhancement of resonant modes. The mode quality factors are calculated from the width of the resonant peaks of the PL spectra, which are about 100 for the ETR with side length of 20 mum.