Realistic forecasting of groundwater level, based on the eigenstructure of aquifer dynamics

Conference paper presented at the MODSIM03, International Congress on Modelling and Simulation, held July 2003, Jupiters Hotel and Casino, Townsville, Queensland.Short-term management of groundwater resources, especially during droughts, can be assisted by forecasts of groundwater levels. Such forecasts need to account for the natural dynamic behaviour of the aquifer, likely recharge scenarios, and recent but unknown abstractions. These requirements mean that forecasts, at say monthly intervals, need to be updated with current observations on a real-time basis. One established procedure for this kind of problem is to fit autoregressive, moving-average, exogenous-variable (ARMAX) time-series models to the history of groundwater levels in response to estimates of land surface recharge. The ARMAX difference equations are then converted into forecast equations that allow real-time updating to include recent forecast errors as an additional source of information. Some disadvantages of this pure time-series analysis approach are the apparent lack of physical concepts in the model formulation and statistical aspects of model identification and calibration that are related to the inherent structure of ARMAX equations. This paper addresses these issues by describing a method for formulating ARMAX forecast equations from a linear system description based on the eigenvalues and eigenvectors (eigenstructure) of the dynamic behaviour of an aquifer. For the piezometric response of a heterogeneous aquifer to a fixed spatial distribution of land surface recharge, with time-varying magnitude, only a few eigenvalues are significant for describing the dynamics. The resulting model has a simple robust parameter structure, and is easily calibrated and implemented in spreadsheet form. The eigenstructure approach enables transfer of some parameter information from locations with good data records to those with sparse data. This modelling approach is demonstrated with monthly values of land surface recharge, estimated from a daily water balance model, and groundwater level data from an observation well in a 2000 km² alluvial aquifer in Canterbury, New Zealand

State-space mixing cell model of unsteady solute transport in unsaturated soil

The purpose of this model is to enable implementation of the theory of linear systems control in operational management of waste and fertiliser applications onto land, so that the underlying groundwater is protected from pollution by leachate. The state-space form of the model enables use of the extensive theory and available software on stochastic linear systems. In particular, the Kalman filter is relevant to the imperfectly understood and highly variable processes of solute transport and transformation in field soils. The series of mixing cells was selected as a linear system model of one-dimensional, vertical, advective-dispersive transport, and based on cumulative soil water drainage as the index variable for application to unsteady flow in unsaturated soil. For each cell, solute transfer between mobile and immobile soil water, as well as equilibrium and nonequilibrium linear adsorption, are represented as lumped processes by two fractions linked by rate-limited transfer. The resident solute concentrations in the cell fractions are the states of the system. The complete model of solute transport and transformation for a uniform soil has four parameters, and can be described in MATLAB® with about ten lines of code. The software library can then be used to produce the discrete form of the model, which is unconditionally stable for any drainage interval as well as to implement state estimation and control algorithms. A demonstration of the model is reported for ³⁵S-labelled sulphate leached from five replicated lysimeters (800 mm diameter, l100 mm depth) of an undisturbed field soil (a free-draining silt loam) under pasture receiving rainfall and irrigation, The results show satisfactory one-step-ahead forecasts with the Kalman filter for the period of record, and a forecast is given of the complete response to the solute pulse application beyond the data record.The reported research is part of the Groundwater Quality Protection programme funded by the Foundation for Research, Science and Technology, New Zealand

Paying More to Get Less: The Effects of External Hiring Versus Internal Mobility

Individuals often enter similar jobs via two different routes: internal mobility and external hiring. I examine how the differences between these routes affect subsequent outcomes in those jobs. Drawing on theories of specific skills and incomplete information, I propose that external hires will initially perform worse than workers entering the job from inside the firm and have higher exit rates, yet they will be paid more and have stronger observable indicators of ability as measured by experience and education. I use the same theories to argue that the exact nature of internal mobility (promotions, lateral transfers, or combined promotions and transfers) will also affect workers’ outcomes. Analyses of personnel data from the U.S. investment banking arm of a financial services company from 2003 to 2009 confirm strong effects on pay, performance, and mobility of how workers enter jobs. I find that workers promoted into jobs have significantly better performance for the first two years than workers hired into similar jobs and lower rates of voluntary and involuntary exit. Nonetheless, the external hires are initially paid around 18 percent more than the promoted workers and have higher levels of experience and education. The hires are also promoted faster. I further find that workers who are promoted and transferred at the same time have worse performance than other internal movers

Politics and Firm Boundaries: How Organizational Structure, Group Interests, and Resources Affect Outsourcing

How does managers\u27 pursuit of their own intraorganizational interests affect decisions about what work to outsource and how to contract with vendors? I study this question using a qualitative study of outsourcing in the information technology department of a large financial services firm. Traditional transaction cost-based theories argue that decisions about which transactions to outsource should reflect the characteristics of those transactions, yet I find only a weak link between transaction characteristics and outsourcing decisions. Qualitative evidence suggests that managers\u27 pursuit of their own intraorganizational interests helps to explain why outsourcing decisions were often divorced from transaction characteristics. I found that the consequences of outsourcing projects were consistent with the assumptions of transaction cost and capabilities-based theories: managers had less authority over outsourced projects than internal ones, those projects were subject to weaker administrative controls, and outsourced vendors provided different capabilities than internal suppliers. However, the way that those consequences were evaluated often reflected managers\u27 own interests rather than those of the organization. I highlight three aspects of organizational structure that affected how managers evaluated outsourcing: the nature of differentiated goals and responsibilities, the administrative controls that managers faced, and the pressures caused by interdependent workflows within the organization. I also show how the distribution of authority and other resources shaped which projects were outsourced. The analysis highlights the value of understanding make-or-buy decisions as an endogenous consequence of the structure in which those decisions take place, rather than as isolated decisions that are maximized regardless of their context

What Happened to Long-Term Employment? The Role of Worker Power and Environmental Turbulence in Explaining Declines in Worker Tenure

Recent declines in the average length of time that U.S. workers spend with a given employer represent an important change in the nature of the employment relationship, yet it is one whose causes are poorly understood. I explore those causes using Current Population Survey data on the tenure of men aged 30–65, from the years 1979–2008. I argue that long-term employment relationships primarily occur when workers pressure employers to close off employment from market competition, reducing the attractiveness of external mobility relative to internal opportunities and increasing employment security. I then explore how two changes in organizations’ environments—a decline in union strength and increased turbulence from changes in technology and globalization—might have affected workers’ ability to secure such closed employment relationships over the last 30 years. My results support the argument that declines in tenure reflect the reduced power of workers to secure closed employment relationships. Recent declines in tenure have been concentrated in large organizations, and many of those declines are explained by controlling for the changing levels of industry unionization. I find little evidence that foreign competition or technological change affected mobility. The results are robust to measures of changing industry growth rates and within-industry reorganization. Supplementary analyses suggest that layoffs are associated with different industry pressures than tenure and that voluntary mobility may have played an important role in declines in tenure

Impact of Physical Activity on Postprandial Lipidemia and Glycemic Control after Chronic Fructose Ingestion

PURPOSE: The overall aim of this study was to examine the effects of a high-fructose diet on postprandial lipemia and hormones associated with glucose control during periods of altered physical activity. METHODS: Twenty-two recreationally active males and females participated in this randomized, cross-over design study (age: 21.2 ± 0.6 years; BMI: 22.6 ± 0.6 kg/m2). Subjects ingested 75 g of fructose for 14 days during a period of high physical activity (FR+Active) (\u3e12,500 steps/day) and a period of low physical activity (FR+Inactive) (\u3c4500 steps/day). Prior to and following the 2 wk loading period, a fructose-rich meal challenge was administered (45% carbohydrate [25% fructose], 40% fat, and 15% protein). Blood was sampled at baseline and for 6 h after the meal and analyzed for triglycerides (TG), very-low density lipoproteins (VLDL), c-reactive protein (CRP), tumor necrosis factor-a (TNF-a), interleukin-6 (IL-6), glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), c- peptide, glucose and insulin concentrations. Area under the curve (AUC) and absolute change from peak to baseline concentrations (Δ peak) were calculated to quantify the postprandial responses. RESULTS: TG, VLDL and IL-6 significantly increased in response to the FR+Inactive intervention (p\u3c0.05), while GIP, insulin, c-peptide and GLP-1 (males only) significantly decreased in response to the FR+Active intervention (p\u3c0.05). No changes occurred with glucose, TNF-a and CRP concentrations for either intervention (p\u3e0.05). CONCLUSIONS: When an inactive lifestyle is adopted for two weeks, while consuming a high fructose diet, postprandial lipidemia and low grade inflammation occurs. In contrast, two weeks of increased physical activity induces positive changes in hormones associated with glucose control in order to attenuate the deleterious effects of the fructose-rich diet

Shifts and Ladders: Comparing the Role of Internal and External Mobility in Managerial Careers

Employees can build their careers either by moving into a new job within their current organization or else by moving to a different organization. We use matching perspectives on job mobility to develop predictions about the different roles that those internal and external moves will play within careers. Using data on the careers of master of business administration alumni, we show how internal and external mobility are associated with very different rewards: upward progression into a job with greater responsibilities is much more likely to happen through internal mobility than external mobility; yet despite this difference, external moves offer similar increases in pay to internal, as employers seek to attract external hires. Consistent with our arguments, we also show that the pay increases associated with external moves are lower when the moves take place for reasons other than career advancement, such as following a layoff or when moving into a different kind of work. Despite growing interest in boundaryless careers, our findings indicate that internal and external mobility play very different roles in executives’ careers, with upward mobility still happening overwhelmingly within organizations

A hermeneutic inquiry into user-created personas in different Namibian locales

Persona is a tool broadly used in technology design to support communicational interactions between designers and users. Different Persona types and methods have evolved mostly in the Global North, and been partially deployed in the Global South every so often in its original User-Centred Design methodology. We postulate persona conceptualizations are expected to differ across cultures. We demonstrate this with an exploratory-case study on user-created persona co-designed with four Namibian ethnic groups: ovaHerero, Ovambo, ovaHimba and Khoisan. We follow a hermeneutic inquiry approach to discern cultural nuances from diverse human conducts. Findings reveal diverse self-representations whereby for each ethnic group results emerge in unalike fashions, viewpoints, recounts and storylines. This paper ultimately argues User-Created Persona as a potentially valid approach for pursuing cross-cultural depictions of personas that communicate cultural features and user experiences paramount to designing acceptable and gratifying technologies in dissimilar locales

Dynamic analysis of groundwater discharge and partial-area contribution to Pukemanga Stream, New Zealand

The proportion and origin of groundwater contribution to streamflow from agricultural catchments is relevant to estimation of the effects of nitrate leached from the soil on the quality of surface waters. This study addresses the partitioning of streamflow contributions from near-surface runoff and from groundwater, each with different contributing land area, on a steep pastoral hillslope in a humid climate. The 3 ha headwater catchment of the perennial Pukemanga Stream, in the North Island of New Zealand, was instrumented for continuous observation of climatic data, streamflow and groundwater level. The dynamics of groundwater levels and groundwater contribution to streamflow were analysed by means of a one-parameter, eigenvalue-eigenfunction description of a 1-D aquifer model. Model results for seven years of daily data predict that 36–44% of the topographical catchment contributes groundwater to the stream. The remaining groundwater generated within the catchment contributes to streamflow outside the catchment. Groundwater was calculated to be 58–83% of observed annual streamflow from the topographical catchment. When the smaller groundwater catchment is taken into account, the groundwater contribution to streamflow is 78–93% on a unit area basis. Concurrent hourly data for streamflow and groundwater levels at two sites indicate the dynamic behaviour of a local groundwater system. Groundwater flow dynamics that support the perennial nature of this headwater stream are consistent with the size of the groundwater body, porosity of the subsurface material, and hydraulic conductivity derived from partitioning of streamflow contributions