Petroleum engineers generate reservoir simulation models to optimize production and maximize recovery. History matching is one of the methods used to calibrate the reservoir models. During traditional history matching, individual model variable parameters (permeability, relative permeability, initial water saturation, etc) are adjusted until the production history is matched using the updated reservoir model. However, this method of utilizing only one model does not help capture the full range of system uncertainty. Another drawback is that the entire model has to be matched from the initial time when matching for new observation data. Ensemble Kalman Filter (EnKF) is a data assimilation technique that has gained increasing interest in the application of petroleum history matching in recent years. The basic methodology of the EnKF consists of the forecast step and the update step. This data assimilation method utilizes a collection of state vectors, known as an ensemble, which are simulated forward in time. In other words, each ensemble member represents a reservoir model (realization). Subsequently, during the update step, the sample covariance is computed from the ensemble, while the collection of state vectors is updated using the formulations which involve this updated sample covariance. When a small ensemble size is used for a large, field-scale model, poor estimate of the covariance matrix could occur (Anderson and Anderson 1999; Devegowda and Arroyo 2006). To mitigate such problem, various covariance conditioning schemes have been proposed to improve the performance of EnKF, without the use of large ensemble sizes that require enormous computational resources. In this study, we implemented EnKF coupled with these various covariance localization schemes: Distance-based, Streamline trajectory-based, and Streamline sensitivity-based localization and Hierarchical EnKF on a synthetic reservoir field case study. We will describe the methodology of each of the covariance localization schemes with their characteristics and limitations.

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This paper examines the timing of initial public offerings and private placements by venture-backed companies. Using a sample of 187 venture-backed IPOs and private placements in a variety of industries between 1991 and 2000 over TSEC and OTC, we find that these companies go public when equity valuationsare high and employ private placements when values are lower. Seasoned venture capital appears to take firms public when industrial equity valuations are higher than their less experienced counterparts. The results are robust to differential specifications of control variables.

Why are initial public offerings (IPOs) underpriced? We consider this is a strategy that insiders use to maximize their personal wealth. When a company offers shares in an initial public offering, insiders typically enter into a lock-up restriction which prohibits insiders from selling their shares within a specified period after the IPO. Insiders interested in maximizing their personal wealth will take actions to maximize the lock-up expiration share price rather than the offer price. When the IPOs underprice, the share price will go up during the honeymoon period. The large run-up in the stock price will attracts interest from the media. And the enhanced coverage brings the stock to the attention of more investors. Then the demand for the stock will increase and make the stock price go up. This allows the insiders to sell shares at the lock-up expiration at price higher than he would otherwise be able to obtain. This study examines the relationship among underpricing, coverage and return. We find that stock deposit and the age of a company are positively correlated with underpricing. The electronic-related companies are much more noticeable than underpricing to lead to more coverage. We also find that coverage is positively correlated with return through the lock-up expiration.

Experiments and direct numerical simulations (DNS) have been performed to examine the e¤ects of initial conditions on the dynamics of a Rayleigh-Taylor unsta- ble mixing layer. Experiments were performed on a water channel facility to measure the interfacial and velocity perturbations initially present at the two-fluid interface in a small Atwood number mixing layer. The experimental measurements have been parameterized for use in numerical simulations of the experiment. Two- and three- dimensional DNS of the experiment have been performed using the parameterized initial conditions. It is shown that simulations implemented with initial velocity and density perturbations, rather than density perturbations alone, are required to match experimentally-measured statistics and spectra. Data acquired from both the exper- iment and numerical simulations are used to examine the role of initial conditions on the evolution of integral-scale, turbulence, and mixing statistics. Early-time turbu- lence and mixing statistics are shown to be strongly-dependent upon the early-time transition of the initial perturbation from a weakly-nonlinear to a strongly-nonlinear flow.

Initial public offerings (IPOs) are primarily valued using the comparable firms approach, whereby underwriters rely heavily on multiples based on the accounting information of peer firms. Effective use of the comparable firms approach depends significantly on the underwriter's ability to estimate the expected future growth and profitability of the IPO firm and its peers and make appropriate adjustments to the multiples to arrive at a final offer price for the IPO shares. I find evidence that, in general, IPO valuations are decreasing relative to peers in the similarity of the peer group to the IPO firm, but this effect is moderated by the peer group's accruals quality. These findings suggest that when peers are similar to the IPO firm, underwriters make less adjustments to the final offer price, however, higher peer accruals quality may ease the assessment of differences in growth and profitability, facilitating further adjustments.

University-based initial teacher education aims at instilling in teacher candidates the idea of the interconnectedness of content, pedagogical and educational research knowledge by allowing meaningful interaction between teacher candidates and teacher educators. The theory-practice divide is presented in the literature as barrier to achieving this goal. This mixed methods research study re-conceptualizes the theory-practice divide from a problem into an opportunity. Secondary school teacher candidates can use contradictions and tensions, surrounding the theory-practice divide, for synthesizing diverse perspectives on content, pedagogical and educational research knowledge. They can integrate this perspective in their practice teaching. The study examined secondary school teacher candidates’ perspectives on the interaction of their content, pedagogical and educational research knowledge in practice teaching as well as factors contributing to these perspectives. The study found that participants’ different perspectives on their research pedagogical and content knowledge (RPACK) were associated with the different levels of their reform-mindedness in mathematics education as measured by a survey. The low, medium and high reform minded participants placed as the first priority pedagogical knowledge, content knowledge and educational research knowledge, respectively.

University-based initial teacher education aims at instilling in teacher candidates the idea of the interconnectedness of content, pedagogical and educational research knowledge by allowing meaningful interaction between teacher candidates and teacher educators. The theory-practice divide is presented in the literature as barrier to achieving this goal. This mixed methods research study re-conceptualizes the theory-practice divide from a problem into an opportunity. Secondary school teacher candidates can use contradictions and tensions, surrounding the theory-practice divide, for synthesizing diverse perspectives on content, pedagogical and educational research knowledge. They can integrate this perspective in their practice teaching. The study examined secondary school teacher candidates’ perspectives on the interaction of their content, pedagogical and educational research knowledge in practice teaching as well as factors contributing to these perspectives. The study found that participants’ different perspectives on their research pedagogical and content knowledge (RPACK) were associated with the different levels of their reform-mindedness in mathematics education as measured by a survey. The low, medium and high reform minded participants placed as the first priority pedagogical knowledge, content knowledge and educational research knowledge, respectively.

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