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For original paper see Carey, ibid., vol. 20, pp. 109-113 (Apr. 1995). This communication provides a generalization of and makes further comments on the original paper. Although the time average acoustic intensity expressions were derived under a far field assumption, it is valid to reference continuous sound sources to time-averaged intensity levels at a distance of 1 m as described. The present author also advocates this convention. A suggested minor notation modification has been presented for a source level convention. The change is put forth to further clarify the convention. In addition, the present communication proposes an additional convention for describing sources which emit isolated transient sounds in terms of energy and the sound source energy level, rather than time averaged power or intensity 相似文献
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Xiaojuan Feng André J. Simpson Bo Elberling David W. Hopkins Ashley D. Sparrow Lawrence G. Greenfield 《Geochimica et cosmochimica acta》2010,74(22):6485-6498
Despite its harsh environmental conditions, terrestrial Antarctica contains a relatively large microbial biomass. Natural abundance carbon and nitrogen stable isotope signatures of organic materials in the dry valleys indicate mixed provenance of the soil organic matter (SOM) with varying proportions of contributions from lichens, mosses, lake-derived algae and cyanobacteria. Here we employed two complementary analytical techniques, biomarker measurements by gas chromatography/mass spectrometry and solution-state 1H nuclear magnetic resonance spectroscopy, to provide further information at a molecular-level about the composition and possible source of SOM in the Garwood Valley, Antarctica. The predominance of branched alkanes and short-chain lipids in the solvent extracts indicates that the primary contribution to the SOM was microbial-derived. Chemical structures in the NaOH extracts from soils were also dominated by amide, peptides, and a CH3-dominating aliphatic region that were characteristic of microbial signatures. Furthermore, the SOM in the Garwood Valley contained compounds that were different from those in the cyanobacteria-dominated mat from a nearby lake (including monoethyl alkanes and enriched side-chain protons). This observation suggests that easily degradable carbon sources from the nearby lake did not dominate the SOM, which is consistent with a fast turnover of the mat-derived organic matter found in the valley. This study highlights the important role of native soil microbes in the carbon transformation and biogeochemistry in terrestrial Antarctica. 相似文献
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Glen Sparrow 《GeoJournal》2001,54(1):73-83
The cities of San Diego and Tijuana have faced each other across the international boundary for over 100 years. The question
raised by this article is whether they comprise a binational city or region. After a brief comparison of their histories,
economies and political systems, a review of some indications of cross border attitudes and a discussion of binational regionalism
as it is impacted by continentalism, it is concluded that the relationship between these cities is driven by factors of economics
not friendship or trust.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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The streamflow over the Yellow River basin is simulated using the PRECIS （Providing REgional Climates for Impacts Studies） regional climate model driven by 15-year （1979-1993） ECMWF reanalysis data as the initial and lateral boundary conditions and an off-line large-scale routing model （LRM）. The LRM uses physical catchment and river channel information and allows streamflow to be predicted for large continental rivers with a 1°×1° spatial resolution. The results show that the PRECIS model can reproduce the general southeast to northwest gradient distribution of the precipitation over the Yellow River basin, The PRECIS- LRM model combination has the capability to simulate the seasonal and annual streamflow over the Yellow River basin. The simulated streamflow is generally coincident with the naturalized streamflow both in timing and in magnitude. 相似文献
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Variation of surface albedo and soil thermal parameters with soil moisture content at a semi-desert site on the western Tibetan Plateau 总被引：11，自引：1，他引：10
Kaicun?Wangwangkaicun@pku.org.cn" title="wangkaicun@mail.iap.ac.cn wangkaicun@pku.org.cn" itemprop="email" data-track="click" data-track-action="Email author" data-track-label="">Email author Pucai?Wang Jingmiao?Liu Michael?Sparrow Shigenori?Haginoya Xiuji?Zhou 《Boundary-Layer Meteorology》2005,116(1):117-129
Almost three years of continuous measurements taken between January 2001 and May 2003 at the Gaize (or Gerze) automatic weather station (32.30 °N, 84.06 °E, 4420 m), a cold semi-desert site on the western Tibetan Plateau, have been used to study seasonal and annual variations of surface albedo and soil thermal parameters, such as thermal conductivity, thermal capacity and thermal diffusivity, and their relationship to soil moisture content. Most of these parameters undergo dramatic seasonal and annual variations. Surface albedo decreases with increasing soil moisture content, showing the typical exponential relation between surface albedo and soil moisture. Soil thermal conductivity increases as a power function of soil moisture content. The diffusivity first increases with increasing soil moisture, reaching its maximum at about 0.25 (volume per volume), then slowly decreases. Soil thermal capacity is rather stable for a wide range of soil moisture content. 相似文献
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Fredrick G. Prahl Jean-François Rontani Margaret A. Sparrow 《Geochimica et cosmochimica acta》2006,70(11):2856-2867
Our specimen of the cultured Emiliania huxleyi strain (CCMP1742, also known as NEPCC55a) that provides the benchmark for -based paleothermometry has started producing, for reasons yet unclear, major amounts of three new alkenones identified as ω15,22-C35 methyl ketone, ω15,22-C36 ethyl ketone and ω16,23-C36 methyl ketone. Comparison of these structures with those established now by the same OsO4 derivatization method applied to the di-unsaturated C37, C38 and C39 alkenones typically found in this organism provides insight into the possible pathway for their biosynthesis. Isothermal batch culture experiments also show the content and composition of these new compounds change systematically and quite significantly in cells when subjected to environmental conditions such as nutrient depletion, variation in light availability and prolonged darkness. Alkenones of similarly unusual short-chain length are evident in suspended particulate materials from present day surface waters in the Ligurian Sea (Mediterranean) and in two different Holocene time horizons (Unit I and Unit II deposits) in Black Sea sediments. However, the positions of the double bonds are different from those that we now report in our culture, implying a different biosynthetic sequence. These alkenones are most likely derived from another, as yet unknown, haptophyte species. If this other organism accounts for all documented occurrences of these compounds in natural samples, then either it has a capacity for growth over a remarkably wide salinity range or surface water salinity in the early Holocene Black Sea may not have been as low as is currently believed. 相似文献
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Turbulent variance characteristics of temperature and humidity over a non-uniform land surface for an agricultural ecosystem in China 总被引：2，自引：0，他引：2
This paper describes the application of the variance method for flux estimation over a mixed agricultural region in China. Eddy covariance and flux variance measurements were conducted in a near-surface layer over a non-uniform land surface in the central plain of China from 7 June to 20 July 2002. During this period, the mean canopy height was about 0.50 m. The study site consisted of grass (10% of area), beans (15%), corn (15%) and rice (60%). Under unstable conditions, the standard deviations of temperature and water vapor density (normalized by appropriate scaling parameters), observed by a single instrument, followed the Monin-Obukhov similarity theory. The similarity constants for heat (CT ) and water vapor (Cq) were 1.09 and 1.49, respectively. In comparison with direct measurements using eddy covariance techniques, the flux variance method, on average, underestimated sensible heat flux by 21% and latent heat flux by 24%, which may be attributed to the fact that the observed slight deviations (20% or 30% at most) of the similarity “constants” may be within the expected range of variation of a single instrument from the generally-valid relations. 相似文献
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Alkenone paleothermometry: Biological lessons from marine sediment records off western South America
Fredrick G. Prahl Alan C. Mix Margaret A. Sparrow 《Geochimica et cosmochimica acta》2006,70(1):101-117
An empirical global core-top calibration that relates the alkenone unsaturation index to mean annual SST (maSST) is statistically the same as that defined for a subarctic Pacific strain of Emiliania huxleyi (CCMP1742) grown exponentially in batch culture under isothermal conditions. Although both equations have been applied widely for paleoSST reconstruction, uncertainty still stems from two key ecological factors: variability in the details of biosynthesis among genetically distinct alkenone-producing strains, and impacts of non-thermal physiological growth factors on . New batch culture experiments with CCMP1742 here reveal that diverge systematically from the core-top calibration in response to nutrient depletion and light deprivation, two physiological stresses experienced by phytoplankton populations in the real ocean. Other aspects of alkenone/alkenoate composition also respond to these stresses and may serve as signatures of such effects, providing an opportunity to detect, understand, and potentially correct for such impacts on the geologic record. A test case documents that sediments from the Southeast Pacific display the alkenone/alkenoate compositional signature characteristic of cells physiologically stressed by light deprivation. Such an observation could be explained if marine snow provided a major vector of sedimentation for these biomarkers. Late Pleistocene records in the Southeast Pacific yield plausible paleotemperature histories of ice-age cooling, but ice-age alkenone/alkenoate signatures fall outside the range of modern calibration samples of similar . They better match core-top samples deposited beneath waters characterized by much cooler maSST, suggesting key features of ice-age ecology for alkenone-producing haptophytes were different from today, and that the index taken alone may misgauge the total range of ice-age cooling at these locations. Analysis of the full spectrum of alkenone/alkenoate compositions preserved in sediments opens up a new opportunity that may improve the accuracy of paleotemperature estimates based on simple analysis and help resolve longstanding disagreements between various paleotemperature reconstruction methods. 相似文献