Utilization of carbon sources in a northern Brazilian mangrove ecosystem     

Tommaso Giarrizzo  Ralf Schwamborn  Ulrich Saint-Paul 《Estuarine, Coastal and Shelf Science》2011

Carbon and nitrogen stable isotope ratios (¹³C and ¹⁵N) and trophic level (TL) estimates based on stomach content analysis and published data were used to assess the contribution of autotrophic sources to 55 consumers in an intertidal mangrove creek of the Curuçá estuary, northern Brazil. Primary producers showed δ¹³C signatures ranging between −29.2 and −19.5‰ and δ¹⁵N from 3.0 to 6.3‰. The wide range of the isotopic composition of carbon of consumers (−28.6 to −17.1‰) indicated that different autotrophic sources are important in the intertidal mangrove food webs. Food web segregation structures the ecosystem into three relatively distinct food webs: (i) mangrove food web, where vascular plants contribute directly or indirectly via POM to the most ¹³C-depleted consumers (e.g. Ucides cordatus and zooplanktivorous food chains); (ii) algal food web, where benthic algae are eaten directly by consumers (e.g. Uca maracoani, mullets, polychaetes, several fishes); (iii) mixed food web where the consumers use the carbon from different primary sources (mainly benthivorous fishes). An IsoError mixing model was used to determine the contributions of primary sources to consumers, based on δ¹³C values. Model outputs were very sensitive to the magnitude of trophic isotope fractionation and to the variability in ¹³C data. Nevertheless, the simplification of the system by a priori aggregation of primary producers allowed interpretable results for several taxa, revealing the segregation into different food webs.  相似文献   

Mid-IR (8–13 μm) images of the 21 μm,carbon rich proto-planetary nebulae     

M. Meixner  J. R. Graham  C. J. Skinner  G. W. Hawkins  E. Keto  J. F. Arens  J. G. Jernigan 《Experimental Astronomy》1994,3(1-4):53-56

We present 9.7 and 11.8 m narrow band (/=10%) images of three carbon (C-) rich proto-planetary nebulae with an unusual 21 m feature: IRAS 07134+ 1005, IRAS 22272+5435, and IRAS 04296+3429. The images were taken at UKIRT using the Berkeley/IGPP/LEA mid-IR camera. All three objects have a bipolar shape adding to the existing evidence that C-rich PPNe are by nature bipolar. Furthermore, we find the same bipolar morphology in a previous study of the C-rich, young planetary nebula, IRAS 21282+5050. We believe these four objects form an evolutionary sequence which links the C-rich asymptotic giant branch (AGB) stars with the C-rich planetary nebulae (PNe). From this evolutionary sequence, we conclude that bipolarity in C-rich PNe begins on the AGB and that the dynamical ages of these PPNe are in fair agreement with theoretical ages for a 0.6 M hydrogen burning core star.  相似文献   

On the red coloration of saltern crystallizer ponds. II. Additional evidence for the contribution of halobacterial pigments   总被引：1，自引：0，他引：1  

Aharon Oren  Zvy Dubinsky 《International Journal of Salt Lake Research》1994,3(1):9-13

In a previous paper we attempted to assess the contribution of red bacteria of theHalobacterium — Haloferax — Haloarcula group and of the -carotene-rich green algaDunaliella salina to the red colour of saltern crystallizer ponds. By means of light absorption measurements, we showed that bacterioruberin contained in the bacteria was mainly responsible for the colour of the brines, in spite of the fact that -carotene derived fromDunaliella was the pigment present in the greatest amount. This apparent discrepancy was explained by the very smallin vivo optical cross-section of -carotene, which is densely packed in globules inside theD. salina cells. We recently observed that the centrifugation technique used in the previous study to collect biomass from the ponds was unsuitable for this type of measurements, as a substantial part of theDunaliella cells present did not sediment upon centrifugation due to the low specific gravity caused by the high -carotene content. Therefore similar measurements were performed with biomass collected by filtration. Again,in vivo absorption spectra were dominated by the absorption peaks of bacterioruberin. The results reported here show that, in spite of the methodological problem associated with the earlier study, all views and conclusions expressed in our earlier paper retain their validity.  相似文献   

Rosat X-ray light curves of early-type stars     

Thomas W. Berghöfer  Jürgen H. M. M. Schmitt 《Astrophysics and Space Science》1994,221(1-2):309-320

We have investigated ROSAT X-ray data of OB stars to search for evidence of time variability in the X-ray emission from early-type stars. As an example for such studies we present a detailed variability analysis for our two program stars Ori and Ori which have been multiply observed with ROSAT. The long-term analysis of both stars now covers a time range of 2.5 years and includes six pointed PSPC observations, an additional pointed HRI observation of Ori and the ROSAT all-sky survey data of both stars. Over a long time range the X-ray light curves of Ori and Ori show no evidence for variability. In the case of Ori we detected a moderate increase in X-ray count rate during a period of 2 days which can be explained as a strong shock propagating in the wind of an O-type star.  相似文献   

Neutron-induced nucleosynthesis     

H. Oberhummer  H. Herndl  T. Rauscher  H. Beer 《Surveys in Geophysics》1996,17(6):665-702

Neutron-induced nucleosynthesis plays an important role in astrophysical scenarios like in primordial nucleosynthesis in the early universe, in the s-process occurring in Red Giants, and in the -rich freeze-out and r-process taking place in supernovae of type II. A review of the three important aspects of neutron-induced nucleosynthesis is given: astrophysical background, experimental methods and theoretical models for determining reaction cross sections and reaction rates at thermonuclear energies. Three specific examples of neutron capture at thermal and thermonuclear energies are discussed in some detail.  相似文献   

Field azimuth disambiguation using ambiguity-free currents     

A. Skumanich  M. Semel 《Solar physics》1996,164(1-2):291-302

Using the ambiguity-free vertical current defined by Semel and Skumanich (1995) we derive a minimum-current azimuth disambiguation for the observed magnetic field in the active region NOAA 7201. A comparison of such a minimum-current azimuth resolution with those from other extant methods indicates that the resulting resolution, even though found to be limited by noise, is a useful first approximation. A comparison of our minimum current distribution with the currents we derive from an extant disambiguation (Lites et al., 1995) indicates the presence of current discontinuities in the form of linear features near the magnetic neutral line of the associated -spot.The National Center for Atmospheric Research is funded by the National Science Foundation  相似文献   

Application of Cesàro mean and the L-curve for the deconvolution problem     

L. Y. ChenJ. T. ChenH. -K. HongC. H. Chen 《Soil Dynamics and Earthquake Engineering》1995,14(5)

In this paper, the Cesàro mean technique is applied to regularize the divergent problem which occurs in ground motion deconvolution analysis in geotechnical engineering. To deal with this ill-posed problem, we use the corner of the L-curve as the compromise point to determine the optimal order of Cesàro mean so that the high frequency content can be suppressed instead of engineering judgement using the concept of a cutoff frequency. The fractional order of Cesàro mean has been derived and used to fulfill this purpose. From the examples shown, it is found that the wave form including maximum acceleration can be accurately predicted and that both the high frequency content and divergent results can be avoided by using the proposed regularization technique.  相似文献   

0－1背包问题的多重分枝－限界算法     

李鸣山  郑海虹 《武汉大学学报(信息科学版)》1995,(1)

建立了０－１背包问题数学模型的一般形式，对通常的分枝一限界算法作了推广，给出了多重分枝一限界算法，有效地解决了具有多个背包的０－１背包问题；也可用于解决某些具有“多重”性质的０－１规划问题。  相似文献   

DZB-1B型自动标定器的幅度测量与标准     

林成桐 《地震地磁观测与研究》1992,(6)

关于地震模拟信号自动标定器输出幅度的测量与校准是一个需要解决的问题。从前我们一直未进行这项工作,国内计量部门也无法解决地震系统常用的超低频信号(0.01Hz—10Hz)的测量与校准问题。我们经过不断探索、研究及反复实验,较好解决了这一问题。  相似文献   

一种高分辨率SAR影像道路提取方法     

刘振宇  余洁 《测绘科学》2017,42(11)

针对高分辨率SAR影像中细节信息损坏道路的面特征结构、影响道路提取,基于影像统计特征,给出一种结合区域生长和细节信息识别的道路提取方法。该方法通过区域生长提取呈现面特征的暗目标(道路框架),利用CFAR算法识别细节,通过形态学融合得到最终结果。为降低高分辨率影像区域异质性对提取结果影响,提出了一种自适应CFAR算法,相比之前算法可自适应删除干扰点;并引入有效表征影像统计的GA0分布。利用海南省陵水黎族自治县机载X波段高分辨率SAR数据的幅度影像进行实验,结果表明,该方法能有效提取呈面特征的道路,获得准确的道路宽度和中心线信息。  相似文献