bluuebunny/crossref_metadata_2025_split huggingface dataset:
MODELING PRIVATE EQUITY FUNDS AND PRIVATE EQUITY COLLATERALISED FUND OBLIGATIONS
Authors: de Malherbe Etienne 
Published: May 2004

The recent development of the securitisation of funds of private equity funds poses the question of the individual and joint modelling of the underlying funds. Private equity funds are different from other managed funds because of their particular bounded life cycle: when the fund starts, the investment partners make an initial capital commitment, the fund managers gradually draw down the committed capital into investments, returns and proceeds are distributed as the investments are realised and the fund is eventually liquidated as the final investment horizon is reached. Modelling private equity funds therefore requires three stages: the modelling of the commitment drawdowns, the modelling of the investment value and the modelling of the return repayments. A standard lognormal process is utilised for the dynamics of the investment value. Squared Bessel processes are utilised for the dynamics of the rates of drawdowns and repayments. Résumé: Le récent développement de la titrisation de fonds de fonds de placements privés pose la question de la modélisation individuelle et jointe des fonds sous-jacents. Les fonds de placements privés sont différents des autres sociétés d'investissement à cause de leur cycle de vie particulier et limité: au démarrage du fonds, les associés s'engagent sur un apport initial en capital; puis les gérants du fonds opèrent des tirages progressifs sur le capital apporté pour procéder à des investissements; les revenus et les profits sont distribués à mesure que les investissements sont réalisés; enfin, le fonds est liquidé lorsque l'horizon d'investissement est atteint. La modélisation d'un fonds doit donc se faire en trois étapes: la modélisation des tirages sur l'apport en capital, la modélisation de la valeur des investissements et enfin la modélisation des paiements et remboursements des dividendes et retours sur investissements. Un processus lognormal standard est utilisé pour la dynamique de la valeur des investissements. Des processus de Bessel carré sont utilisés pour la dynamique des taux de tirage et de remboursement.
The Australian Air Quality Forecasting System. Part III: Case Study of a Melbourne 4-Day Photochemical Smog Event
Authors: Tory K. J. , Cope M. E. , Hess G. D. , Lee S. , Puri K. , Manins P. C. , Wong N. 
Published: May 2004

Abstract
A 4-day photochemical smog event in the Melbourne, Victoria, Australia, region (6–9 March 2001) is examined to assess the performance of the Australian Air Quality Forecasting System (AAQFS). Although peak ozone concentrations measured during this period did not exceed the 1-h national air quality standard of 100 ppb, elevated maximum ozone concentrations in the range of 50–80 ppb were recorded at a number of monitoring stations on all four days. These maximum values were in general very well forecast by the AAQFS. On all but the third day the system predicted the advection of ozone precursors over Port Phillip (the adjacent bay) during the morning, where, later in the day, relatively high ozone concentrations developed. The ozone was advected back inland by bay and sea breezes. On the third day, a southerly component to the background wind direction prevented the precursor drainage over the bay, and the characteristic ozone cycle was disrupted. The success of the system's ability to predict peak ozone at individual monitoring stations was largely dependent on the direction and penetration of the sea and bay breezes, which in turn were dependent on the delicate balance between these winds and the opposing synoptic flow.
The Australian Air Quality Forecasting System. Part I: Project Description and Early Outcomes
Authors: Cope M. E. , Hess G. D. , Lee S. , Tory K. , Azzi M. , Carras J. , Lilley W. , Manins P. C. , Nelson P. , Ng L. , Puri K. , Wong N. , Walsh S. , Young M. 
Published: May 2004

Abstract
The Australian Air Quality Forecasting System (AAQFS) is the culmination of a 3-yr project to develop a numerical primitive equation system for generating high-resolution (1–5 km) short-term (24–36 h) forecasts for the Australian coastal cities of Melbourne and Sydney. Forecasts are generated 2 times per day for a range of primary and secondary air pollutants, including ozone, nitrogen dioxide, carbon monoxide, sulfur dioxide, and particles that are less than 10 μm in diameter (PM10). A preliminary assessment of system performance has been undertaken using forecasts generated over a 3-month demonstration period. For the priority pollutant ozone it was found that AAQFS achieved a coefficient of determination of 0.65 and 0.57 for forecasts of peak daily 1-h concentration in Melbourne and Sydney, respectively. The probability of detection and false-alarm rate were 0.71 and 0.55, respectively, for a 60-ppb forecast threshold in Melbourne. A similar level of skill was achieved for Sydney. System performance is also promising for the primary gaseous pollutants. Further development is required before the system can be used to forecast PM10 confidently, with a systematic overprediction of 24-h PM10 concentration occurring during the winter months.
Assessment of the Aviation Weather Center Global Forecasts of Mesoscale Convective Systems*
Authors: Ziv Baruch , Yair Yoav , Presman Karin , Füllekrug Martin 
Published: May 2004

Abstract
This paper examines the precision of location and top height of mesoscale convective systems, as forecast by the Aviation Weather Center (AWC). The examination was motivated by the Mediterranean Israeli Dust Experiment (MEIDEX) on the space shuttle Columbia, aimed to image transient luminous events (TLEs), such as sprites, jets, and elves, from orbit. Mesoscale convective systems offer a high probability for the occurrence of TLEs above active thunderstorms. Because the operational methodology was planned around a 24-h cycle, there was a need for a global forecast of areas with a high probability of massive thunderstorms that are prone to exhibit TLE activity. The forecast was based on the high-level significant weather (SIGWX) maps, commonly used for civil aviation, provided by the AWC on the Internet. To estimate the operational skill of this forecast for successfully detecting clouds with a high probability for producing TLEs, predictions for selected dates were compared with satellite observations. The locations of 66 mesoscale cloud systems on Significant Weather Maps, produced for eight different dates in August 2001, were compared with satellite global IR images for these dates. Operational skill was determined as the percentage of observed cloud systems found within a 5° range in the regions that appeared on the forecast maps as having the potential to contain thunderclouds and was found to be 92%. No consistent error was found in location. The predicted size of the convective system was typically larger than the observed size. Cloud-top heights of 53 systems were examined on four dates in October–November 2001, using IR radiances converted to brightness temperatures. For each convective system, the coldest cloud-top temperature was converted to height, using the NCEP–NCAR reanalysis data for the respective location and time. The standard error in the forecast heights was 2516 m. Because the purpose was to get true alerts of potential TLE occurrences, operational forecast skill was defined as the percentage of forecasts that were accurate within 1000 m or higher than observed. The 1000-m tolerance was allowed because of inevitable uncertainties underlying this method of analysis. Operational skill was found to be only 43%. During the “STS-107” mission flown in January 2003, the forecasted areas of main convective centers were transmitted daily to the crew and helped them in pointing the cameras and targeting thunderstorms. This ensured the success of the MEIDEX sprite observations that recorded numerous events in many different geographical locations.
Can generic paediatric mortality scores calculated 4 hours after admission be used as inclusion criteria for clinical trials?
Authors: Leteurtre Stéphane , Leclerc Francis , Wirth Jessica , Noizet Odile , Magnenant Eric , Sadik Ahmed , Fourier Catherine , Cremer Robin 
Published: May 2004

Abstract
Introduction
Two generic paediatric mortality scoring systems have been validated in the paediatric intensive care unit (PICU). Paediatric RISk of Mortality (PRISM) requires an observation period of 24 hours, and PRISM III measures severity at two time points (at 12 hours and 24 hours) after admission, which represents a limitation for clinical trials that require earlier inclusion. The Paediatric Index of Mortality (PIM) is calculated 1 hour after admission but does not take into account the stabilization period following admission. To avoid these limitations, we chose to conduct assessments 4 hours after PICU admission. The aim of the present study was to validate PRISM, PRISM III and PIM at the time points for which they were developed, and to compare their accuracy in predicting mortality at those times with their accuracy at 4 hours.

Methods
All children admitted from June 1998 to May 2000 in one tertiary PICU were prospectively included. Data were collected to generate scores and predictions using PRISM, PRISM III and PIM.

Results
There were 802 consecutive admissions with 80 deaths. For the time points for which the scores were developed, observed and predicted mortality rates were significantly different for the three scores (P < 0.01) whereas all exhibited good discrimination (area under the receiver operating characteristic curve ≥0.83). At 4 hours after admission only the PIM had good calibration (P = 0.44), but all three scores exhibited good discrimination (area under the receiver operating characteristic curve ≥0.82).

Conclusions
Among the three scores calculated at 4 hours after admission, all had good discriminatory capacity but only the PIM score was well calibrated. Further studies are required before the PIM score at 4 hours can be used as an inclusion criterion in clinical trials.
A practical method for estimating effective parameters of anisotropy from reflection seismic data
Authors: Isaac J. Helen , Lawton Don C. 
Published: May 2004

The location of any event imaged by P‐wave reflection seismic data beneath a tilted transversely isotropic (TTI) overburden is shifted laterally if isotropic velocities are used during data processing. The magnitude of the shift depends on five independent parameters: overburden thickness, angle of tilt, symmetry‐axis velocity, and the Thomsen anisotropy parameters and δ. The shift also varies with source–receiver offset. We have developed a procedure to estimate these five parameters when the tilt of the symmetry axis from the vertical is equal to the dip of the TTI layer (except in the special cases transverse isotropy with vertical or horizontal axis of symmetry). We observe three attributes of seismic data processed using isotropic velocities: the zero‐offset arrival time of a selected reflection, the difference in arrival time between a near‐offset and a far‐offset arrival, and the difference in imaged location (smear) of this target event between the same offsets. We then perform a cascaded scan of the five parameters to determine those combinations of the five that result in calculated attributes equivalent to the observed attributes. The multiple solutions are averaged to give the parameter estimates. Application of this method to synthetic and physical model reflection data results in multiple solutions, which are constrained and averaged to obtain the effective imaging parameters. These effective parameters are close estimates of the true model parameters in both cases. For field seismic data this procedure requires that there be a suitable observable event below the TTI overburden and assumes that the measured times and shifts are reasonably accurate.
Processing of anisotropic data in the τ‐pdomain: I—Geometric spreading and moveout corrections
Authors: van der Baan Mirko 
Published: May 2004

Stacking of seismic data is conventionally done in the time‐offset domain. This has the disadvantage that geometric spreading must be removed before true‐amplitude processing can be attempted. This inconvenience arises since wave motion in the time‐offset domain is determined by spherical waves. Plane waves in layered media, on the other hand, are not subject to geometric spreading. Hence, processing of both isotropic and anisotropic data in such media benefits from first applying a plane‐wave decomposition such as a proper τ‐p transform. The resulting τ‐p gathers can be flattened and stacked over slowness. Subsequent time differentiation is needed to counter the loss of high frequencies during stacking. This approach has the advantage that the geometric spreading is removed without prior knowledge of the actual (an)isotropic velocity field and without any need to pick traveltimes or moveout velocities. Subsequent moveout corrections naturally require knowledge of the velocityfield.The proposed methodology is exact for 3D data volumes and arbitrary anisotropy in laterally homogeneous media or for 2D acquisition lines over 1D, isotropic media or over 1D, transversely isotropic media with vertical axis of symmetry (VTI). It relies on the same principles as more conventional geometric spreading corrections and time‐offset stacking. In many respects, it is even more flexible. For instance, geometric spreading has been correctly removed for all present wave modes and types simultaneously (primary, multiple, pure‐mode, and converted waves), and nonhyperbolic moveout resulting from isotropic layering is also taken into account. In addition, head waves may now contribute constructively to the stacked section. Moreover, both multiple elimination and predictive deconvolution are straightforward and known to yield very good results in the τ‐p domain. The resulting stacked section can then be used for any poststack processing such as time migration.
Efficient automatic denoising of gravity gradiometry data
Authors: de Oliveira Lyrio Julio Cesar Soares , Tenorio Luis , Li Yaoguo 
Published: May 2004

Gravity gradiometry data are prized for the high frequency information they provide. However, as any other geophysical data, gravity gradient measurements are contaminated by high‐frequency noise. Separation of the high‐frequency signal from noise is a crucial component of data processing. The separation can be performed in the frequency domain, which usually requires tuning filter parameters at each survey line to obtain optimal results. Because a modern gradiometry survey generates more data than a traditional gravity survey, such time‐consuming manual operations are not very practical. In addition, they may also introduce subjectivity into the process.To address this difficulty, we propose an automatic, data‐adaptive 1D wavelet filtering technique specially designed to process gravity gradiometry data. The method is based on the thresholding of the wavelet coefficients to filter out high‐frequency noise while preserving localized sharp signal features. We use an energy analysis across scales (specific for gravity gradiometry data) to select denoising thresholds and to identify sharp features of interest. We compare the proposed method with traditional Fourier‐domain filters by applying them to synthetic data sets contaminated with either correlated or uncorrelated noise. The results demonstrate that the proposed filter is efficient and, when applied in the fully automated mode, produces results that are comparable to the best results achievable through frequency‐domain filters. We further illustrate the method by applying it to a set of gravity gradiometry data acquired in the Gulf of Mexico and by characterizing the removed noise. Both synthetic and field examples show that the proposed method is an efficient and better alternative to other traditional frequency domain methods.
Finite‐difference modeling of viscoelastic materials with quality factors of arbitrary magnitude
Authors: Asvadurov Sergey , Knizhnerman Leonid , Pabon Jahir 
Published: May 2004

To minimize acoustic noise, designers of sonic logging tools often consider coatings of viscoelastic materials with very high attenuation properties. Efficient finite‐difference modeling of viscoelastic materials is a topic of current research. To model viscoelastic materials in the time domain through finite differences efficiently, one needs to replace the time convolution, which enters in the stress–strain relations, by a set of first‐order differential equations. This procedure is equivalent to computing a rational approximation of a certain form to the frequency‐dependent complex modulus of viscoelasticity. Known schemes for computing such approximations are designed to treat materials with low attenuation, such as underground formations, but fail to produce accurate or even physically meaningful results for highly attenuative materials. We propose a novel scheme that allows one to construct, for a given frequency range, a uniformly optimal rational approximation for the most widely used model of materials with constant quality (Q‐) factors of arbitrary magnitude. We present the proof of convergence and demonstrate it on numerical finite‐difference examples. These examples also demonstrate the effective transparency of a simple tool modeled as a pipe of highly viscoelastic material. For frequency‐dependent quality factors we present a modified numerical scheme to compute a nearly optimal rational approximation of the viscoelastic modulus.
Experiments with a Miniature Piezocone in Thinly Layered Soil
Authors: Hird CC , Sangtian N 
Published: May 2004

Abstract
A piezocone, with a cross-sectional area of 100 mm2 and a pore pressure filter either at its apex or at its shoulder, was driven at the standard rate of 20 mm/s into samples of thinly layered soil. The samples consisted of alternating layers of normally consolidated kaolin clay about 18 mm thick and layers of fine sand or silt about 2 mm thick enclosed in a 252-mm-diameter rigid-walled cell. The performance of the piezocone was evaluated with respect to the detection of the more permeable layers during penetration and the estimation of the coefficient of consolidation from pore pressure dissipation tests in a clay layer at the end of penetration. Control tests were performed on two clay samples without any sand or silt layers. Changes in the pore pressure response enabled the more permeable layers within the layered samples to be easily detected, but their spacing was too close for individual layers to be detected using the cone resistance profile. Generally, the detection obtained from pore pressures was better with the apex filter than with the shoulder filter. The permeable layers had a measurable influence on the dissipation test results, but their influence on the derived values of the coefficient of consolidation was never large by comparison with their effect on the overall consolidation behavior of the soil.
Leak-Free Pressure Plate Extractor For Measuring the Soil Water Characteristic Curve
Authors: Wang X , Benson CH 
Published: May 2004

Abstract
A new pressure plate extractor, referred to as the leak-free pressure plate extractor (LFPPE), is described where air leakage around the ceramic plate effectively is eliminated. The LFPPE was designed so that it would be robust, easy to use, and readily assembled and disassembled for testing and maintenance. An example shows that the LFPPE yields a soil water characteristic curve (SWCC) that is consistent with portions of the SWCC measured with other independent methods (chilled mirror hygrometer and hanging column). A testing procedure is also described that has been employed for measuring numerous SWCCs with the LFPPE without an incident of air leakage.
Characterization of a Fiberglass Geotextile for Unsaturated In-Plane Water Transport
Authors: Stormont JC , Ramos R 
Published: May 2004

Abstract
The methods and results of the characterization of a woven, multifilament fiberglass geotextile are described in this paper. The moisture characteristic curve was measured with capillary rise and hanging column methods for both wetting and drying paths. In-plane flow was first measured with a simple siphon test, followed by measurement of the unsaturated transmissivity using a constant suction permeameter. The fiberglass geotextile became transmissive during wetting at a suction of 100 mm, and remained transmissive during drying to a suction of 600 mm. A lateral drainage test with the fiberglass geotextile indicated that the geotextile accepted and laterally drained water infiltrating through a soil layer under suctions in excess of 600 mm. The fiberglass geotextile is shown to contain more water and is more transmissive at greater suctions compared to other geotextiles, and has considerable capacity to drain water under suction.
True Triaxial Testing System for Clay with Proportional-Integral-Differential (PID) Control
Authors: Mandeville D , Penumadu D 
Published: May 2004

Abstract
A flexible boundary electro-pneumatic true triaxial system has been developed for testing cohesive soil. The system is capable of applying principal stresses on each face of a cubical specimen using a Proportional-Integral-Differential (PID) based closed loop control algorithm. This device has the ability to measure both the internal and external pore pressures for a 102-mm cubical specimen and uses custom developed Butyl rubber membranes. Measurement of the internal pore pressure is accomplished using a needle piezometer. Appropriate software has been developed that can automatically perform saturation, isotropic or Ko consolidation, and shear testing under stress or strain control along various stress or strain paths. Using this system, results from isotropically consolidated triaxial compression and triaxial extension stress paths are presented for cubical kaolin specimens. Comparative tests using conventional cylindrical specimens using lubricated ends were also performed. Issues related to the interference of the flexible membranes, uniformity of strains and bifurcations, interpreted friction angles, and undrained shear strength are discussed.
Effect of Freeze-Thaw on the Permeation of Arctic Diesel Through a GCL
Authors: Rowe RK , Mukunoki T , Li MH , Bathurst RJ 
Published: May 2004

Abstract
The hydraulic conductivity of a scrim reinforced nonwoven thermal locked geosynthetic clay liner (GCL) with respect to both de-aired distilled water and arctic diesel (jet fuel) are examined for different numbers of freeze and thaw cycles. The hydraulic conductivity of jet fuel is found to be about one order of magnitude smaller than that for de-aired water. Increasing numbers of freeze and thaw cycles, did not significantly change the hydraulic conductivity although the permittivity with respect to water decreased. The intrinsic permeability of the GCL permeated by jet fuel increased slightly with an increasing number of freeze-thaw cycles. It is shown that under the conditions examined, the GCL performed very well.
A Device for Determination of Thermal Properties of Soil
Authors: Krishnaiah S , Singh DN 
Published: May 2004

Abstract
This paper deals with the details of a device we call the thermal property detector, THERMODET, which can be used for easily determining soil thermal properties such as thermal resistivity, diffusivity, and specific heat in the laboratory. Details of the fabrication of the device, its working methodology, and analysis of the results are presented in the paper. To demonstrate the efficiency of the device, studies have been conducted on soils with totally different properties such as clay, silty soil, and sand. It was determined that THERMODET works quite efficiently and is a reliable device for determining soil thermal properties.