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排序方式: 共有197条查询结果,搜索用时 15 毫秒
121.
In the Hudson Canyon experiment, a sound source moved at a constant depth in 73 m of water while transmitting four tonals. The signal was received on a vertical array of hydrophones that spanned the water column. The data set from this experiment has become a standard test case for studying source tracking using matched field processing. As part of that process it was important to first determine a suitable environment model and demonstrate the feasibility of matched-field processing. In this paper, we provide the background on the original data processing that was done to accomplish this. Several interesting results emerged from that study. Frequency averaging was demonstrated to be extremely beneficial when used with the Bartlett processor. However, the popular Minimum Variance processor performed poorly. Finally we discuss a very simple approach to combining the energy coherently that provided significantly improved results. 相似文献
122.
We comment on the recent paper by Dwivedi and Pandey (Solar Physics
216, 59, 2003). Parts of that paper closely reproduce, without reference, material that we had published previously, while other
parts that deviate from our earlier analysis contain several critical flaws. We show that magnetoacoustic waves are capable
of heating the corona with a modest enhancement in the coefficient of compressive viscosity. 相似文献
123.
Philip W. Porter 《The Professional geographer》1988,40(3):337-339
124.
Summary. Epicentres of microearthquakes detected by two ocean-bottom seismographs deployed on the Reykjanes Ridge at latitude 59° N can be interpreted as trending between 010° and 020° E of N, parallel to detailed morphological features seen in the area, rather than the overall trend of the ridge (036° E of N). Travel times from an airgun source to the seismographs indicate much slower P wave velocities for the top 4 km at the ridge crest compared with that 5–10 km off axis. 相似文献
125.
Trevor J. Porter Michael F. J. Pisaric Robert D. Field Steven V. Kokelj Thomas W. D. Edwards Peter deMontigny Richard Healy Allegra N. LeGrande 《Climate Dynamics》2014,42(3-4):771-785
High-latitude δ18O archives deriving from meteoric water (e.g., tree-rings and ice-cores) can provide valuable information on past temperature variability, but stationarity of temperature signals in these archives depends on the stability of moisture source/trajectory and precipitation seasonality, both of which can be affected by atmospheric circulation changes. A tree-ring δ18O record (AD 1780–2003) from the Mackenzie Delta is evaluated as a temperature proxy based on linear regression diagnostics. The primary source of moisture for this region is the North Pacific and, thus, North Pacific atmospheric circulation variability could potentially affect the tree-ring δ18O-temperature signal. Over the instrumental period (AD 1892–2003), tree-ring δ18O explained 29 % of interannual variability in April–July minimum temperatures, and the explained variability increases substantially at lower-frequencies. A split-period calibration/verification analysis found the δ18O-temperature relation was time-stable, which supported a temperature reconstruction back to AD 1780. The stability of the δ18O-temperature signal indirectly implies the study region is insensitive to North Pacific circulation effects, since North Pacific circulation was not constant over the calibration period. Simulations from the NASA-GISS ModelE isotope-enabled general circulation model confirm that meteoric δ18O and precipitation seasonality in the study region are likely insensitive to North Pacific circulation effects, highlighting the paleoclimatic value of tree-ring and possibly other δ18O records from this region. Our δ18O-based temperature reconstruction is the first of its kind in northwestern North America, and one of few worldwide, and provides a long-term context for evaluating recent climate warming in the Mackenzie Delta region. 相似文献
126.
This paper provides historical context for contemporary discourses on landownership, notably the changing scale of absentee landownership and foreign ownership since 1849. Trends in landownership since European occupation of one of the most agriculturally productive regions in south east Australia, the Lachlan River catchment, are examined at regional, shire and district scales. Evolution of tenure indicates that absentee landowners owned most of the land until after 1935, but between the 1860s and 1970 the proportion of landowners who were resident landowners increased. In 1970, resident landowners owned most land. Since 1970, absentee landownership has increased, the most dramatic increase occurring after 1990. By 2009, absentee landownership had reached the high levels of 1849. While most contemporary types of landowners have historical antecedents, new trends include changes in the country of origin of foreign investors, increased small property ownership by city-based individuals and the establishment of Indigenous incorporated ownership. 相似文献
127.
Ebrahim Ahmadisharaf Alfred J. Kalyanapu Jason R. Lillywhite Gina L. Tonn 《水文科学杂志》2013,58(12):1776-1790
ABSTRACTThis study presents a probabilistic framework to evaluate the impact of uncertainty of design rainfall depth and temporal pattern as well as antecedent moisture condition (AMC) on design hydrograph attributes – peak, time to peak, duration and volume, as well as falling and rising limb slopes – using an event-based hydrological model in the Swannanoa River watershed in North Carolina, USA. Of the six hydrograph attributes, falling limb slope is the most sensitive to the aforementioned uncertainties, while duration is the least sensitive. In general, the uncertainty of hydrograph attributes decreases in higher recurrence intervals. Our multivariate analysis revealed that in most of the return periods, AMC is the most important driver for peak, duration and volume, while time to peak and falling limb slope are most influenced by rainfall pattern. In higher return periods, the importance of rainfall depth and pattern increases, while the importance of AMC decreases. 相似文献
128.
An Evaluation of Sources of Nitrogen as Causes of Ground-Water Contamination in Nassau County, Long Island 总被引:1,自引:0,他引:1
Keith S. Porter 《Ground water》1980,18(6):617-625
129.
Ylitalo GM Stein JE Hom T Johnson LL Tilbury KL Hall AJ Rowles T Greig D Lowenstine LJ Gulland FM 《Marine pollution bulletin》2005,50(1):30-39
Wild California sea lions (Zalophus californianus) have an unusually high prevalence of neoplasms (18% of stranded dead adults) and high levels of contaminants. The contribution of organochlorine (OC) tissue burdens to the probability of sea lions dying from carcinoma was explored using a logistic regression model. Levels of PCBs and DDTs were determined in blubber of sea lions diagnosed with metastatic carcinoma and animals that had died from non-carcinoma-related incidents (e.g., gunshot, domoic acid poisoning). Animals with carcinoma had higher mean concentrations (based on wet weight) of PCBs and DDTs (more than 85% and 30% higher, respectively) in blubber than did sea lions without carcinoma; the highest concentrations of OCs in the sea lions affected with carcinoma were measured in the males. Blubber thickness was significantly different between the two groups of sea lions, but after controlling for this difference, there was still a significant effect of PCBs, but not DDTs, on the probability of sea lions dying with carcinoma. Age, sex, mass and length did not affect the probability of dying from carcinoma. 相似文献
130.