991 resultados para Cellini, Benvenuto, 1500-1571.


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The crinoid fauna of the continental margin (0-1500 m) of northeastern North America (Georgia to Canada) includes 14 species in 13 genera and 5 families. We introduce the external morphology and natural history of crinoids and include a glossary of terms, an illustrated key to local taxa, annotated systematic list, and an index. The fauna includes 2 species found no further south than New England and 8 that occur no further north than the Carolinas and Blake Plateau. Comactinia meridionalis (Agassiz) is the only species commonly found in shallow water «50 m). No taxa are endemic to the area. (PDF file contains 34 pages.)

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纳米氧化锌(ZnO)是一种直接宽带隙半导体材料,室温下其禁带隙宽为本3.37 eV,激子束缚能为60 meV。纳米ZnO有明显的尺寸效应、表面和界面效应等,物理化学性能优越。在压电材料、铁电材料、平面显示、表面声波、传感器、场发射器件、激光、光催化等方面有着广泛的用途。近年来,对纳米ZnO材料的研究成为国内外的一个热点。 本论文研究了用化学气相沉积(CVD)法制备微/纳米ZnO材料。通过控制实验条件,合成了多种特殊结构和形貌的微/纳米ZnO材料,并用扫描电子显微镜(SEM)、高分辨率透射电镜(HR-TEM)、X-射线衍射仪(XRD)、Raman光谱和光致发光(PL)等对材料的结构和光学性能进行了表征。采用CVD法,在温度为630 °C,氧气流量为15 sccm,氩气流量为300 sccm的条件下,制备了一种纳米带冠四足状ZnO(T-ZnO)。此结构ZnO材料的每根足顶端均有一规则的六方帽形结构,具有很大的比表面积。实验结果表明:合成的ZnO材料为纤维锌矿结构单晶,并且沿着(0001)方向生长;室温下的PL谱有两个激发峰,一个是在393 nm处相对较弱的近带紫外峰,另一个是在511 nm处强峰。而材料在600 °C下氧气中退火30 min后,511 nm附近的绿光激发辐射峰则基本消失了,这说明在511 nm处的绿光激发辐射峰可能是由于氧空位引起的。此外,通过改变实验条件,还得到了其他多种结构的微/纳米ZnO材料。 通过大量实验,找到了一种在低温下合成微/纳米ZnO材料的新方法,即水蒸气氧化法。用ZnI2作为锌源,水蒸气作为氧化剂,实验温度在300~500 °C范围内,大大低于通常CVD法的500~1500 °C。采用此法,用硅做基底,得到了一系列有趣的实验结果,大多数情况下ZnO纳米晶自组装成很规则的圆。而在瓷舟中收集到的纳米ZnO跟普通CVD法结果相似,可以得到锥状、棒状等结构的纳米晶,但其生长方式与硅基底上的有很大差别。此外,用水蒸气氧化法,还实现了ZnO纳米晶在碳纳米管(CNTs)上的直接生长,而且其PL性能增强,这可能是纳米ZnO和CNTs相互耦合的结果。在700 °C温度下,以锌粉和ZnI2作为锌源,用水蒸气作为氧化剂,在硅基底的正反面分别得到了纳米棒和纳米推子阵列。此外,还对水蒸气氧化法的化学反应机理进行了分析,实验结果证明:固态ZnI2在受热和一定真空度下先蒸发成ZnI2分子,ZnI2分子遇到水蒸气发生反应生成偶极ZnO分子,这些ZnO偶极分子在硅基底上通过静电力自组装成特殊的几何形状。 此外,还通过分子动力学模拟的方法,对材料的力学性能进行了研究,得到了ZnO的弹性常数和体弹性模量,模拟值跟其他研究人员的实验和模拟结果吻合得很好,并估出算了ZnO晶体的表面能和断裂韧性。 本论文还对制备材料的光催化性能进行了系统的研究,采用CVD法制备ZnO,对铬黑T(EBT)进行光催化降解实验。通过正交实验方法,得到了ZnO催化降解EBT的最佳工艺条件,即催化剂用量为5 g/L,光照强度为120 W,反应温度为20 °C,反应时间为120 min,EBT浓度为10 mg/L,溶液pH值为4。 在最佳实验条件下,20分钟内有95%的EBT被降解完,30分钟内则全部降解。因此,ZnO在EBT的降解中催化效率很高,在废水处理中具有潜在的应用前景。

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About 1500 ovaries of Baltic cod were prepared for estimating the potential absolute and relative individual fecundity. The female cod were sampled in the Belt Sea, ICES Subdivision (SD) 22, in the Arkona Sea, SD 24, and in the Bornholm Sea, SD 25. The investigations started in1992 and until 1999 cruises were carried out to catch female cod in the different sub-divisions every year. The results shows that the potential fecundity is not a stable biological parameter, and that significant changes are possible within a relative short period. It was demonstrated that the developments of the potential individual fecundity of the western (Gadus morhua morhua) and eastern Baltic cod stocks (Gadus morhua callarias) were different. In contrast to the stable individual fecundity of the western cod the absolute and relative fecundity of the eastern repeat spawners increased from 1993 to 1999, significantly. The reason of this development seems to be the dramatic decrease of the eastern cod stock and the more successful reproduction of individuals that produce oocytes with a lower dry weight in combination with a higher relative fecundity.

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国家自然科学基金项目(30730032/10702075)

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We experimentally observe the formation of X-waves at fundamental, third harmonic, and fifth harmonic wavelengths by infrared (central wavelength at similar to 1500 nm) femtosecond laser pulse filamentation in air. By fitting the angularly resolved spectra of the fundamental and harmonic waves using X-wave relations, we confirm that all the X-waves have nearly the same group velocity, indicating that they are locked in space and time during their propagation in filament.

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In this thesis I apply paleomagnetic techniques to paleoseismological problems. I investigate the use of secular-variation magnetostratigraphy to date prehistoric earthquakes; I identify liquefaction remanent magnetization (LRM), and I quantify coseismic deformation within a fault zone by measuring the rotation of paleomagnetic vectors.

In Chapter 2 I construct a secular-variation reference curve for southern California. For this curve I measure three new well-constrained paleomagnetic directions: two from the Pallett Creek paleoseismological site at A.D. 1397-1480 and A.D. 1465-1495, and one from Panum Crater at A.D. 1325-1365. To these three directions I add the best nine data points from the Sternberg secular-variation curve, five data points from Champion, and one point from the A.D. 1480 eruption of Mt. St. Helens. I derive the error due to the non-dipole field that is added to these data by the geographical correction to southern California. Combining these yields a secular variation curve for southern California covering the period A.D. 670 to 1910, with the best coverage in the range A.D. 1064 to 1505.

In Chapter 3 I apply this curve to a problem in southern California. Two paleoseismological sites in the Salton trough of southern California have sediments deposited by prehistoric Lake Cahuilla. At the Salt Creek site I sampled sediments from three different lakes, and at the Indio site I sampled sediments from four different lakes. Based upon the coinciding paleomagnetic directions I correlate the oldest lake sampled at Salt Creek with the oldest lake sampled at Indio. Furthermore, the penultimate lake at Indio does not appear to be present at Salt Creek. Using the secular variation curve I can assign the lakes at Salt Creek to broad age ranges of A.D. 800 to 1100, A.D. 1100 to 1300, and A.D. 1300 to 1500. This example demonstrates the large uncertainties in the secular variation curve and the need to construct curves from a limited geographical area.

Chapter 4 demonstrates that seismically induced liquefaction can cause resetting of detrital remanent magnetization and acquisition of a liquefaction remanent magnetization (LRM). I sampled three different liquefaction features, a sandbody formed in the Elsinore fault zone, diapirs from sediments of Mono Lake, and a sandblow in these same sediments. In every case the liquefaction features showed stable magnetization despite substantial physical disruption. In addition, in the case of the sandblow and the sandbody, the intensity of the natural remanent magnetization increased by up to an order of magnitude.

In Chapter 5 I apply paleomagnetics to measuring the tectonic rotations in a 52 meter long transect across the San Andreas fault zone at the Pallett Creek paleoseismological site. This site has presented a significant problem because the brittle long-term average slip-rate across the fault is significantly less than the slip-rate from other nearby sites. I find sections adjacent to the fault with tectonic rotations of up to 30°. If interpreted as block rotations, the non-brittle offset was 14.0+2.8, -2.1 meters in the last three earthquakes and 8.5+1.0, -0.9 meters in the last two. Combined with the brittle offset in these events, the last three events all had about 6 meters of total fault offset, even though the intervals between them were markedly different.

In Appendix 1 I present a detailed description of my standard sampling and demagnetization procedure.

In Appendix 2 I present a detailed discussion of the study at Panum Crater that yielded the well-constrained paleomagnetic direction for use in developing secular variation curve in Chapter 2. In addition, from sampling two distinctly different clast types in a block-and-ash flow deposit from Panum Crater, I find that this flow had a complex emplacement and cooling history. Angular, glassy "lithic" blocks were emplaced at temperatures above 600° C. Some of these had cooled nearly completely, whereas others had cooled only to 450° C, when settling in the flow rotated the blocks slightly. The partially cooled blocks then finished cooling without further settling. Highly vesicular, breadcrusted pumiceous clasts had not yet cooled to 600° C at the time of these rotations, because they show a stable, well clustered, unidirectional magnetic vector.

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Bi-doped BaF2 crystal was grown by the temperature gradient technique and its spectral properties were investigated. The absorption, emission and excitation spectra were measured at room temperature. Two broadband emissions centered at 1070 and 1500 nm were observed in Bi-doped BaF2 crystal. This extraordinary luminescence should be ascribed to Bi-related centers at distinct sites. We suggest Bi2+ or Bi+ centers adjacent to F vacancy defects are the origins of the observed NIR emissions. (C) 2009 Optical Society of America

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We experimentally investigate the generation of high-order harmonics in a 4-mm-long gas cell using midinfrared femtosecond pulses at various wavelengths of 1240 nm, 1500 nm, and 1800 nm. It is observed that the yield and cutoff energy of the generated high-order harmonics critically depend on focal position, gas pressure, and size of the input beam which can be controlled by an aperture placed in front of the focal lens. By optimizing the experimental parameters, we achieve a cutoff energy at similar to 190 eV with the 1500 nm driving pulses, which is the highest for the three wavelengths chosen in our experiment.

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4 p.