Evaluating and re-demarcating the Hospital Service Areas in Florida

The Hospital Service Areas (HSAs) better portray underlying local patterns of hospitalization than administrative units, and offer a promising analysis unit for studies of healthcare market. The widely used Dartmouth HSAs in the U.S. were solely based on Medicare inpatient records about two decades ago. Our analysis used all discharge records from Florida hospitals in the 2011 Healthcare Cost and Utilization Project (HCUP) dataset from the Agency for Healthcare Research and Quality (AHRQ). We first matched Medicare-paid hospitalization records in 2011 to the Dartmouth HSAs for demonstrating the temporal variation of the Medicare-derived HSAs. We then compared the HSA configurations based on the overall hospitalization records to Medicare-derived HSAs in the same year (2011) for assessing the representativeness of the Medicare-derived HSAs. Results indicate the boundaries of the Medicare-derived HSAs have significantly shifted over two decades and are inadequate in representing the overall population. The Huff model was used to generate more solid HSAs than traditional approaches.     

Pacific Ocean observation programs: Gaps in ecological time series

How well do existing ocean observation programs monitor the oceans through space and time? A meta-analysis of ocean observation programs in the Pacific Ocean was carried out to determine where and how key parameters defining the physics, chemistry, and biology of the oceans were measured. The analysis indicates that although the chemistry and physics of the Pacific Ocean are reasonably well monitored, ecological monitoring remains largely ad hoc, patchy, unsystematic, and inconsistent. The California Cooperative Oceanic Fisheries Investigations (CalCOFI), for example, is the only Pacific Ocean program in which the zooplankton and micronekton are resolved to species with consistent time series of greater than 20 years duration. Several studies now indicate massive changes to nearshore, mesopelagic and other fish communities of the southern California Current but available time series do not allow these potential changes to be examined more widely. Firm commitment from the global community to sustained, representative, quantitative marine observations at the species level is required to adequately assess the ecological status of the oceans.     

Direct time domain analysis of floating structures with linear and nonlinear mooring stiffness in a 3D numerical wave tank

In this paper, motion response of a moored floating structure interacting with a large amplitude and steep incident wave field is studied using a coupled time domain solution scheme. Solution of the hydrodynamic boundary value problem is achieved using a three-dimensional numerical wave tank (3D NWT) approach based upon a form of Mixed-Eulerian–Lagrangian (MEL) scheme. In the developed method, nonlinearity arising due to incident wave as well as nonlinear hydrostatics is completely captured while the hydrodynamic interactions of radiation and diffraction are determined at every time step based on certain simplifying approximations. Mooring lines are modelled as linear as well as nonlinear springs. The horizontal tension for each individual mooring line is obtained from the nonlinear load-excursion plot of the lines computed using catenary theory, from which the linear and nonlinear line stiffness are determined. Motions of three realistic floating structures with different mooring systems are analyzed considering various combinations of linear and approximate nonlinear hydrodynamic load computations and linear/nonlinear mooring line stiffness. Results are discussed to bring out the influence and need for consideration of nonlinearities in the hydrodynamics and hydrostatics as well as the nonlinear modelling of the line stiffness.     

Mechanistic interpretation of alpine glacierized environments: Part 1. Model formulation and related dynamical properties

Understanding the long-term seasonal dynamics of alpine glacierized basins is essential to evaluating their relation to climatic forcing. We focus on process knowledge by following a minimalist approach, and propose a spatially lumped nonlinear differential model (MIAGE) to describe the link between the volume V of water that is stored on the basin and the river runoff Q at the seasonal scale. We formulate the model structure by mathematically describing the link relating precipitation P, temperature T, river runoff Q and stored volumes V. Beside reproducing some typical features of the catchment hydrology of glacierized basins, MIAGE offers an explanation of their seasonal hydroclimatic behaviour and of the origin of their dissipative properties from a dynamical system perspective. By studying the model nonlinear properties, characteristics, and performances, we show that climatic change has both direct and feedback effects on such basins. Eventually a synchronization of the runoffs with either the precipitation trend or the temperature trend may occur depending on the storage conditions. This model is subsequently used in a companion paper in order to investigate the potential impact of climatic change scenarios on basins of the Italian and Swiss Alps [Mechanistic interpretation of alpine glacierized environments: Part 2. Hydrologic interpretation and model parameters identification on case study, this issue].     

Time Evolution of Deformation Using Time Series of Differential Interferograms: Application to La Palma Island (Canary Islands)

Differential interferometry is a very powerful tool for detecting changes in the Earth’s crust where coherence conditions are good, but is difficult to employ in some volcanic areas due to dense vegetation. We apply two differential InSAR methods using the time series associated with the interferograms to perform a phase analysis on a data set for La Palma island (Canary Islands) from the ERS-1 and ERS-2 European Space Agency (ESA) satellites for the time period 1992 to 2000. Both methods involve choosing a master image from the database and creating a series of interferograms with respect to this image. The “Coherent Pixel Time Series” (CPTS) technique chooses pixels with good average coherence, aligns the unwrapped interferograms with a stable area and then performs an inversion to calculate the linear velocity to quantify the deformation. The Coherent Target Modeling (CTM) method calculates the temporal coherence of each pixel to identify stable targets and then determines the best velocity for each pixel by using a linear fit that maximizes the temporal coherence. Using these two methods we have been able to detect deformation on La Palma Island that has been previously undetectable by conventional InSAR methods. There is a roughly circular region on the Southern part of the island that is actively deforming at ~ −4 to −8 mm/yr. This region is located near the Teneguia valcano, the host of the last known eruption on La Palma in 1971. A thorough investigation of the possible sources for this deformation revealed that it was most likely created by a subsurface thermal source.     

A comparison between artificial neural network algorithms and empirical equations applied to submerged weir scour evolution prediction

Estimating the time evolution of a local scour hole downstream of submerged weirs can help determine the maximum scour depth and length and is essential to designing submerged weir foundations.In the current study, artificial neural networks with a backpropagation learning algorithm were used to estimate the temporal variation of scour profiles downstream of submerged weirs under clear water conditions. Physical factors, such as the flow condition, weir size, and sediment characteristics, are ge...     

Simultaneous joint migration inversion for high-resolution imaging/inversion of time-lapse seismic datasets

The current time-lapse practice is to exactly repeat well-sampled acquisition geometries to mitigate acquisition effects on the time-lapse differences. In order to relax the rigid requirements on acquisition effects, we propose simultaneous joint migration inversion as an effective time-lapse tool for reservoir monitoring, which combines a joint time-lapse data processing strategy with the joint migration inversion method. Joint migration inversion is a full-wavefield inversion method that explains the measured reflection data using a parameterization in terms of reflectivity and propagation velocity. Both the inversion process inside the imaging/inversion scheme and the extra illumination provided by including multiples in joint migration inversion makes the obtained velocity and reflectivity operator largely independent of the utilized acquisition geometry and, thereby, relaxes the strong requirement of non-repeatability during the monitoring. Because simultaneous joint migration inversion inverts for all datasets simultaneously and utilizes various constraints on the estimated reflectivities and velocity, the obtained time-lapse differences have much higher accuracy compared to inverting each dataset separately. It allows the baseline and monitor parameters to communicate with each other dynamically during inversion via a user-defined spatial weighting operator. In order to get more localized time-lapse velocity differences, we further extend the regular simultaneous joint migration inversion to a robust high-resolution simultaneous joint migration inversion process using the time-lapse reflectivity difference as an extra constraint for the velocity estimation during inversion. This constraint makes a link between the reflectivity- and the velocity difference by exploiting the relationship between them. We demonstrate the feasibility of the proposed method with a highly realistic synthetic model based on the Grane field offshore Norway and a time-lapse field dataset from the Troll Field.     

基于GPS连续运行基准站的中国区域共模误差研究

共模误差是GPS台站位置时间序列中的主要误差源之一,分离和消除共模误差可以探测到原先淹没在噪音中的微弱信号。本文对中国260个卫星导航定位基准站2011～2018年的数据进行处理,获得了位置时间序列,采用主成分分析（PCA）方法对其扣除构造运动等形变信号后的残差序列进行区域共模误差分析。结果表明,PCA方法有效地提取了中国区域共模误差,经过滤波后时间序列的信噪比明显提高,第一主分量空间分布均一,第二主分量空间分布呈现明显的梯度变化,表明第二主分量不是少数台站的局部效应,是对第一主分量的补充和修正,中国区域的共模误差分析不能忽略二阶分量。对振幅调制的影响进行了对比分析,发现顾及振幅调制的共模误差不仅明显减弱了年周期的特征,还显著降低了闪烁噪声,表明由于参数过于简化而未被估计的“信号”会演变成共模误差,未被正确模型化的“信号”会影响区域滤波的准确性。     

环境负载对云南地区基准站时间序列的噪声模型特性研究

以云南地区27个GPS基准站坐标时间序列为研究对象,使用赤池信息量和贝叶斯信息量估计准则（AIC/BIC）对其进行噪声分析,计算并扣除时间序列中大气负载、非潮汐海洋负载和水文负载3种环境负载引起的位移量,得到各基准站分量在环境负载改正前后的最优噪声模型。结果表明,部分基准站分量经过负载改正后最优噪声模型会发生变化,改正前后的大部分基准站噪声特性均体现为闪烁+白噪声和幂律噪声。环境负载对基准站的垂向位移影响比水平向更为显著,水文负载成为影响基准站的最大因素,最大位移量达到厘米级。分析环境负载改正前后噪声特性的变化表明,环境负载改正在U分量上的影响最大,N分量次之,E分量最小,噪声模型的变化在地域上并未呈现明显规律。     

Marine transient electromagnetic sounding of deep buried hydrocarbon reservoirs: principles,methodologies and limitations

The possibility of a time‐domain electromagnetic sounding method using excitation and measurement of vertical electric fields to search for and identify deeply buried reservoirs of hydrocarbons offshore is investigated. The method operates on source–receiver offsets, which are several times less than the depth of the reservoir. Geoelectric information is obtained from the transient responses recorded in the pauses between the pulses of electric current in the absence of the source field. The basics of the method, as well as its sensitivity, resolution, and the highest accessible depth of soundings for various geological conditions in a wide range of sea depths, are analyzed. For the analysis, 1D and 3D geoelectric models of hydrocarbon reservoirs are used. It is shown that under existing technologies of excitation and measurement of vertical electric fields, the highest accessible depth of soundings can be up to 4 km. Technology for the inversion and interpretation of transient responses is demonstrated on experimental data.