共查询到20条相似文献，搜索用时 31 毫秒
1.
Hospital service areas (HSAs) are increasingly adopted as a basic analysis unit for health care studies. The popular Dartmouth HSAs were produced more than two decades ago, and the process was far from automated. This research uses a Huff-based model automated in a geographic information systems (GIS) environment to delineate HSAs. Based on the Florida State Inpatient Database (SID) in 2011, a best-fitting distance decay function is derived from the actual travel patterns of hospitalization and then fed into the Huff model to strengthen the model's theoretical foundation in individual spatial behavior. The HSAs derived from the Huff-based model are then compared to the traditional flow-based HSAs defined by the Dartmouth method and assessed in terms of self-containment and heterogeneity of internal socioeconomic structure and urbanicity. The Huff-based model requires fewer data and is easy to implement as an automated toolkit and thus has great potential for replication in other regions to define large-scale and consistent HSAs. 相似文献
2.
Hospital service areas (HSAs) capture most of local patient-to-hospital travel flows, and have been accepted as the most basic unit for analyzing local hospital utilization and hospitalization patterns. If a given HSA includes multiple hospitals providing care for its residents, it is complicated to assign responsibility for small-area variation in hospital performance or healthcare costs to specific hospitals without established HSA managers. The goal of this study is to produce HSAs with the fewest number of hospitals within an HSA unit. Only a very limited number of studies are related to the HSA delineation. This study reviews the existing approaches to delineate a broader range of service areas besides HSAs. A spatial algorithm named Travel-to-Hospital Algorithm (TTHA) was developed and implemented using the individual hospital discharge records from the Florida State Inpatient Database for 2011. The final output, named the TTHA-derived HSAs, included 14 more eligible divisions in Florida than the HSAs produced by the traditional approach (92 vs. 78), with the degree of self-containment comparable between the two sets of HSAs. The TTHA provides insight into the patterns of hospital visits and holds great value for the delineation of other types of service and catchment areas. 相似文献
3.
Hospital service area (HSA) and hospital referral region (HRR), known as a hierarchical HSA system, have been used as analysis units in a growing body of large‐scale studies of healthcare spending, utilization, and outcome in the United States. However, the popular Dartmouth HSAs and HRRs were produced more than two decades ago and are unable to represent contemporary healthcare markets. This research uses a revised Huff Model to delineate two levels of hospital service areas in Florida, resulting in sixty‐four HSAs nested in twenty‐one HRRs. Three elements distinguish our method from existing work. First, a best‐fitting distance‐decay function derived from the actual travel pattern of hospitalization is embedded in the Huff Model to strengthen the model's theoretical foundation in individual spatial behavior. Secondly, the hierarchal central place structure is supported by the differing travel‐friction coefficients for general versus specialized patients; general patients experience a steeper gradient and thus a shorter average travel range that supports delineating more HSAs of smaller area size, and specialized patients exhibit a flatter gradient and thus a longer average travel range that leads to fewer HRRs of large‐sized areas. Finally, the delineation method automated in geographic information systems (GIS) can be easily replicated in other regions to define large‐scale and consistent hierarchical HSA systems. 相似文献
4.
Improving maternal health is one of the Sustainable Development Goals. Hospital service areas (HSAs), which contain most hospitalization behaviors at the local scale, are crucial for health care planning. However, little attention has been given to HSAs for maternal care and the hierarchy structure. Considering Hubei, central China, as a case study, this study aims to fill these gaps by developing a method for delineating hierarchical HSAs for maternal care using a network optimization approach. The approach is driven by actual patient flow data and has an explicit objective to maximize the modularity. It also establishes the hierarchical structure of maternal care HSAs, which is fundamental for the planning of hierarchical maternal care and referral systems. In our case study, 45 secondary HSAs and 22 tertiary HSAs are delineated to achieve maximal modularity. The HSAs perform well in terms of indices such as the Localization Index and Market Share Index. Furthermore, there is a complementary relationship between secondary and tertiary hospitals, which suggests the need for referral system planning. This study can provide evidence for the validity of the HSA and the planning of maternal care HSAs in China. It also provides transferable methods for planning hierarchical HSAs in other developing countries. 相似文献
5.
1959年来珠江三角洲地区的海平面变化与趋势 总被引：5，自引：0，他引：5
验潮站资料的低空间分辨率与卫星数据的短时序是区域海平面变化研究存在的关键难题。本文结合卫星高度计海平面高度距平资料及验潮站数据,基于EOF和最小二乘法重建过去53 年（1959-2011 年）珠江三角洲海平面变化时空序列,并利用主成分分析方法建立区域统一海平面变化时间序列。结果显示,基于EOF和最小二乘法的海平面高度场重建方法能很好地解决卫星高度计资料时间序列不长和验潮站分布稀缺时间不连续等问题,对于海平面变化研究,尤其是关于过去长期的变化过程及特征研究适用性良好。对统一海平面变化时间序列线性拟合显示,近53 年珠江三角洲区域海平面平均变化速率为4.08 mm/yr,且存在近期加速上升趋势。与单站研究相比,该方法较好地表达了区域海平面主要变化特征并剔除可能存在的噪音。径流及厄尔尼诺现象也对珠江三角洲海平面空间变化产生影响。 相似文献
6.
Helen Bennion Carl D. Sayer Stewart J. Clarke Thomas A. Davidson Neil L. Rose Ben Goldsmith Ruth Rawcliffe Amy Burgess Gina Clarke Simon Turner Emma Wiik 《Journal of Paleolimnology》2018,60(2):329-348
Aquatic macrophytes play a key role in providing habitat, refuge and food for a range of biota in shallow lakes. However, many shallow lakes have experienced declines in macrophyte vegetation in recent decades, principally due to eutrophication. As changes in macrophyte composition and abundance can affect overall ecological structure and function of a lake, an assessment of the timing and nature of such changes is crucial to our understanding of the wider lake ecosystem. In the typical absence of historical plant records, the macro-remains of macrophytes preserved in lake sediments can be used to assess long-term changes in aquatic vegetation. We generated recent (150–200 years) plant macrofossil records for six English lakes subject to conservation protection to define past macrophyte communities, assess trajectories of ecological change and consider the implications of our findings for conservation targets and strategies. The data for all six lakes reveal a diverse submerged macrophyte community, with charophytes as a key component, in the early part of the sedimentary records. The stratigraphies indicate considerable change to the aquatic vegetation over the last two centuries with a general shift towards species more typically associated with eutrophic conditions. A common feature is the decline in abundance of low-growing charophytes and an increase in tall canopy-forming angiosperms such as fine-leaved Potamogeton species, Zannichellia palustris and Callitriche species. We hypothesise, based on findings from long-term datasets and palaeoecological records from enriched shallow lakes where plants are now absent, that the observed shifts provide a warning to managers that the lakes are on a pathway to complete macrophyte loss such that nutrient load reduction is urgently needed. It is the sound understanding of present-day plant ecology that affords such reliable interpretation of the fossil data which, in turn, provide valuable context for current conservation decisions. 相似文献
7.
1990年以来中国小麦农业气象灾害时空变化特征 总被引：4，自引：0，他引：4
利用1991-2009 年中国农业气象站点记录的灾害及物候资料,首先对小麦各类气象灾害发生的频次及所在生长发育期进行了时空特征分析;然后通过对比较暖10 年（2000-2009）与其前10（1990-1999）年两个时期的灾害时空变化特点,探讨气候变化对灾害发生的影响。结果表明：干旱是小麦发生频率最高的灾害类型,其发生频率高达79.21%,冰雹、干热风、大风、连阴雨等灾害类型也在小麦生产过程中有较多发生。气候变化背景下,小麦典型气象灾害发生频次有所增加,并且主要发生在生殖生长期。空间上,灾害类型增加较为明显的有：山东半岛的干热风、西北地区东部的干旱、暴雨及冰雹。分析表明：不同灾害种类的发生及变化的空间分布与中国气候变化特征有很强的关系。 相似文献
8.
Predicting the Peak in World Oil Production 总被引：1，自引：0，他引：1
The US Department of Energy's Energy Information Administration (EIA) recently predicted that world oil production could continue to increase for more than three decades, based on the recent US Geological Survey (USGS) evaluation of world oil resources and a simple, transparent model. However, it can be shown that this model is not consistent with actual oil production records in many different regions, particularly that of the US, from which it was derived. A more careful application of the EIA model, using the same resource estimates, indicates that at best non-OPEC oil production can increase for less than two decades, and should begin to decline at the latest sometime between 2015 and 2020. OPEC at this point will completely control the world oil market and will need to meet increased demand as well as compensate for declining production of non-OPEC producers. OPEC could control the market even sooner than this, given its larger share of proven oil reserves, probable difficulties in transforming non-OPEC undiscovered reserves into proven reserves, and the converging interests of all oil producers as reserves are depleted. This has significant implications for the world economy and for US national security. 相似文献
9.
Shuang Qing Liu Zu Han Liu Wei Guo Wang Yue Ping Lu Xiao Liang Zhu Bin Guo 《寒旱区科学》2018,10(3):232-239
Based on the hydrological data in the headwater region of the Kaidu River during 1972–2011, the multifractal process of runoff fluctuation was analyzed. Results indicated that, in the past 40 years, the overall runoff of the Kaidu River in Xinjiang has shown significant multifractal behavior. Its singular curve lnχ_q(ε)–ln(ε) verified a favorable scale invariance over the entire time scale. τ(q)–q proved that evolution of the runoff time series presented multifractal characteristics. Moreover,the multifractal spectrum f(α)–α curve was hooklike leftward which indicated that, compared to relatively large runoff events. And Δf0 indicated that these relatively small events took the leading role; B0 explained the Kaidu River's daily-runoff ascending tendency presented during 1972–2011. Besides that, the multifractal behavior of the Kaidu River's runoff variability over four decades was also analyzed. Generally speaking, by decades, their four corresponding spectrum variations were not noticeable. These Δα values showed larger runoff events occupied the leading position with some local values falling. During the 1970 s to the 1990 s, Δf0 illustrated the probability of the daily runoff at the lowest point is always larger than that of the highest during three continuous decades. At the beginning of the 21 st century, for Δf0 the trend presented was contrary from the 1970 s to the 1990 s. B values suggested an overall trend of increases during1972–2011. Until the 21 st century, the runoff with a slightly descending tendency on the whole explained these relatively large runoff events taking the leading role for the Kaidu River; but sometimes, some small events also played the dominant role. 相似文献
10.
HY-2是中国自主研发的海洋卫星。 本文研究了利用HY-2卫星扫描微波辐射计亮温数据反演北极海冰密集度的方法。参考NASA TEAM方法,我们对典型海区光谱梯度率和极化梯度率进行了统计分析,确定了计算海冰密集度所需的亮温特征值;利用天气滤波器有效去除了开阔海域由于大气中水蒸气、云中液态水、降雨等现象引起的海冰密集度计算错误。本文计算了2012年全年的北极海冰密集度产品并对产品精度进行了初步验证,验证结果表明：三个海冰类型已知区域的海冰密集度结果与理想值比较接近,多年冰密集度的反演精度需要进一步提高;本文结果与美国冰雪数据中心和德国不来梅大学提供的两种业务化海冰密集度产品一致。本研究为利用HY-2卫星监测极区海冰密集度变化,发布实时产品奠定了基础。 相似文献
11.
Land subsidence in the western San Joaquin Valley has been studied and monitored for almost six decades. Especially in the 1950s and 1960s, land subsidence had tremendous negative environmental and socioeconomic implications. The rate of land subsidence in the Los Banos–Kettleman City area, however, has decreased during the last three decades as a result of a decrease in groundwater withdrawal, following the importation of surface water to the Valley in late 1960s. The land subsidence in the Valley potentially could be a serious issue if the existing surface water supplies cannot meet increasing water demands during future critical drought periods. In this respect, this paper proposes a preliminary analysis to predict magnitudes of subsidence for the period 2000 to 2040, based on historical occurrences. In this study, extrapolation from earlier subsidence is based on: (1) knowledge of recent post-drought records at extensometers, (2) assumption of a single time porosity scenario, and (3) the premise that pumpage from the confined aquifer gradually will decrease as a result of progressive water quality degradation. Predicted magnitudes of land subsidence in the Los Banos–Kettleman City area are expected to be in the range 0.5 to 4.0 m for the next 4 to 5 decades under the scenario considered in this paper. [Key words: subsidence, groundwater extraction, aquitard, inelastic compaction, active porosity, Los Banos-Kettleman City, California.] 相似文献
12.
中国区域经济协同发展的驱动因素——基于哈肯模型的分阶段实证研究 总被引：3，自引：0，他引：3
运用哈肯模型对影响中国区域经济协同发展的驱动因素进行实证研究,以发现控制区域经济系统演化的序参量。分析了区域经济协同发展的内涵及基本特征,从区域比较优势(RCA)、区域经济联系(RER)和区域产业分工(RID)三个方面解析了区域经济协同发展的驱动因素;运用协同学中的哈肯模型对1992-2001年、2002-2011年20年间中国29省市经济协同发展驱动因素进行分阶段序参量识别,结果表明：中国区域经济协同发展的序参量由1992-2001年的RCA转变为2002-2011年的RCA和RID,表明中国进入协同发展新阶段;后10年（2002-2011年）与前10年（1992-2001年）相比,呈现出以下特征：市场分割程度降低,协同发展环境得到优化;区域经济协同发展从初级阶段跃升至中级阶段;中西部地区后发优势逐步显现,三大地区梯级差异缩小。 相似文献
13.
Detecting land-use change has become of concern to environmentalists, conservationists and land use planners due to its impact on natural ecosystems. We studied land use/land cover (LULC) changes in part of the northwestern desert of Egypt and used the Markov-CA integrated approach to predict future changes. We mapped the LULC distribution of the desert landscape for 1988, 1999, and 2011. Landsat Thematic Mapper 5 data and ancillary data were classified using the random forests approach. The technique produced LULC maps with an overall accuracy of more than 90%. Analysis of LULC classes from the three dates revealed that the study area was subjected to three different stages of modification, each dominated by different land uses. The use of a spatially explicit land use change modeling approach, such as Markov-CA approach, provides ways for projecting different future scenarios. Markov-CA was used to predict land use change in 2011 and project changes in 2023 by extrapolating current trends. The technique was successful in predicting LULC distribution in 2011 and the results were comparable to the actual LULC for 2011. The projected LULC for 2023 revealed more urbanization of the landscape with potential expansion in the croplands westward and northward, an increase in quarries, and growth in residential centers. The outcomes can help management activities directed toward protection of wildlife in the area. The study can also be used as a guide to other studies aiming at projecting changes in arid areas experiencing similar land use changes. 相似文献
14.
蒸散是地球表层物质循环与能量交换过程的重要组成部分,了解其时空特征和影响因素具有重要的科学意义。以鄱阳湖流域为研究区,基于WaSSI-C生态水文模型,利用气象数据、叶面积指数数据和土壤数据等估算1983-2011年鄱阳湖流域蒸散,分析其时空特征,并通过情景模拟定量分析植被恢复和气候变化对蒸散的影响。研究表明：鄱阳湖流域蒸散多年均值变化范围为741~914 mm/a,植被和降水量分布是造成流域蒸散空间差异的主要原因;近三十年来鄱阳湖流域蒸散呈阶段性增长趋势,增长率为1.495 mm/a;植被、气温和降水对鄱阳湖流域蒸散的单独影响均为正向,但气温和降水的联合效应会导致蒸散下降;鄱阳湖流域蒸散变化的主导因素具有空间差异性,从整体上看,植被恢复是驱动蒸散呈增加趋势的主要原因,而气候变化是导致蒸散年际波动的主要原因。 相似文献
15.
M. Ali H. Oda A. Hayashida K. Takemura & M. Torii 《Geophysical Journal International》1999,136(1):218-228
We have conducted a palaeomagnetic study on three sediment cores obtained from a single site in Lake Biwa, central Japan. A total of 1430 discrete samples from three cores show strong and stable remanence, which is carried by pseudo-single-domain magnetite. Palaeomagnetic records from individual cores show little scatter of directions, and there is excellent correlation among the records from the site. A composite palaeomagnetic secular variation (PSV) record for the Holocene was constructed after fine-scale adjustment and stacking of the three records. The age model is based on two wide-spread tephra layers: Kawagodaira (3150 yr BP, calendar years) and Kikai-Akahoya (7250 yr BP). Our results show that the declinations and inclinations are strikingly similar to archaeomagnetic data from southwest Japan for the last 2000 years. The PSV record from Lake Biwa shows good correlation in directions with that of Beppu Bay, located about 500 km west of Lake Biwa, although the Beppu Bay record shows relatively smaller amplitudes of both inclination and declination, probably due to heavy smoothing of the initial results. When the Lake Biwa record is compared with the proposed type curve for southwest Japan, there is considerable disagreement throughout the Holocene. A re-analysis of the data sets and other information used to construct the type curve revealed that the discrepancy in the results was due to inadequate age determination for the cores used in previous studies. We conclude that the stacked PSV record from Lake Biwa meets the criteria required for a reliable curve. Moreover, our results resolve the complications found in the correlation of PSV records in southwest Japan and thereby contribute to a better understanding of Holocene PSV. 相似文献
16.
We propose a vertical array analysis method that decomposes complex seismograms into body and surface wave time histories by using a velocity structure at the vertical array site. We assume that the vertical array records are the sum of vertically incident plane P and S waves, and laterally incident Love and Rayleigh waves. Each phase at the surface is related to that at a certain depth by the transfer function in the frequency domain; the transfer function is obtained by Haskell's matrix method, assuming a 1-D velocity structure. Decomposed P , S and surface waves at the surface are estimated from the vertical array records and the transfer functions by using a least-squares method in the frequency domain; their time histories are obtained by the inverse Fourier transform. We carried out numerical tests of this method based on synthetic vertical array records consisting of vertically incident plane P and S waves and laterally incident plane Love and Rayleigh waves. Perfect results of the decomposed P , S , Love and Rayleigh waves were obtained for synthetic records without noise. A test of the synthetic records in which a small amount of white noise was added yielded a reasonable result for the decomposed P , S and surface waves. We applied this method to real vertical array records from the Ashigara valley, a moderate-sized sedimentary valley. The array records from two earthquakes occurring at depths of 123 and 148 km near the array (epicentral distance of about 31 km) exhibited long-duration later phases. The analysis showed that duration of the decomposed S waves was a few seconds and that the decomposed surface waves appeared a few seconds after the direct S -wave arrival and had very long duration. This result indicated that the long-duration later phases were generated not by multireflected S waves, but by basin-induced surface waves. 相似文献
17.
18.
An overall greening over the Tibetan Plateau(TP) in recent decades has been established through analyses of remotely sensed Normalized Difference Vegetation Index(NDVI), though the regional pattern of the changes and associated drivers remain to be explored. This study used a satellite Leaf Area Index(LAI) dataset(the GLASS LAI dataset) and examined vegetation changes in humid and arid regions of the TP during 1982–2012. Based on distributions of the major vegetation types, the TP was divided roughly into a humid southeastern region dominated by meadow and a dry northwestern region covered mainly by steppe. It was found that the dividing line between the two regions corresponded well with the lines of mean annual precipitation of 400 mm and the mean LAI of 0.3. LAI=0.3 was subsequently used as a threshold for investigating vegetation type changes at the interanual and decadal time scales: if LAI increased from less than 0.3 to greater than0.3 from one time period to the next, it was regarded as a change from steppe to meadow, and vice versa. The analysis shows that changes in vegetation types occurred primarily around the dividing line of the two regions, with clear growth(reduction) of the area covered by meadow(steppe), in consistency with the findings from using another independent satellite product. Surface air temperature and precipitation(diurnal temperature range) appeared to contribute positively(negatively) to this change though climate variables displayed varying correlation with LAI for different time periods and different regions. 相似文献
19.
甘肃省气温与降水变化趋势及其对主要流域径流量的影响 总被引：1，自引：0，他引：1
基于气温和降水格点资料及水文站年径流量数据,对甘肃省不同区域气候变化趋势及其与径流量的关系进行了分析。结果显示:1961-2011年,甘肃省大部地区气温呈显著升高趋势(p<0.05),而降水量则在乌鞘岭东西两侧地区存在明显的反向变化趋势。气温和降水的变化趋势对不同区域径流量起不同作用。过去51年来,在乌鞘岭以西地区,受河源区降水量增加的影响,黑河与疏勒河流域径流量有增加趋势;在乌鞘岭以东地区,由于降水量减少及气温升高,区域河流径流量以减少趋势为主。虽然气温和降水对径流量均有影响,但降水与径流量的关系更为密切。然而从长时间尺度来看,虽然甘肃省区域平均降水量无明显减少趋势,但径流量仍呈现减少趋势,可能与气温持续上升趋势带来的蒸发增强、水分损耗增加等因素有关。 相似文献
20.
Jaime Escobar Thomas J. Whitmore George D. Kamenov Melanie A. Riedinger-Whitmore 《Journal of Paleolimnology》2013,49(2):237-252
We examined the anthropogenic lead (Pb) burden that accumulated in sediment of lakes in the southeastern USA during the last ~150 years. Mining, smelting, agriculture, and fossil-fuel combustion are known to have contributed to Pb pollution in lakes of other regions. Few studies, however, have examined Pb sequestered in lakes of the southeastern USA, particulary peninsular Florida, which is subject to less continental atmospheric influence than other regions of the eastern USA. We obtained sediment cores from Little Lake Jackson and Little Lake Bonnet in Highlands County, Florida and used Pb isotopes in the records to identify principal sources of Pb contamination. The sediment records showed that changes in Pb concentration and isotope ratios correspond temporally with gasoline consumption in the USA, as well as with changes in lead ores used to produce leaded gasoline. Lead concentrations in the study lakes showed temporal variations that were similar to those found in peat records from east-central Florida. Isotope trends were similar to the mean USA atmospheric Pb deposition record, and to Pb isotope records from Bermuda and Atlantic corals. We modeled the isotopic composition of the anthropogenic Pb in lake sediments and found that the overall trend is controlled by Pb that was released during leaded gasoline combustion. There is, however, additional Pb at each site that comes from sources that are not fully represented by the natural, background Pb. Lead isotope ratios and Pb/arsenic (As) ratios provide evidence that Pb deposition in lakes during the middle 1900s might have been influenced by lead arsenate applications to golf courses, a source that is often ignored in Pb isotope studies. Isotope evidence confirms, however, that following cessation of commercial lead arsenate use in the 1960s, atmospheric alkyl lead was again the primary influence on Pb in sediments of the study lakes. 相似文献