Relationship Between Renal Function and Functional Decline: Role of the Estimating Equation
Pedone, Claudio; Corsonello, Andrea; Bandinelli, Stefania; Pizzarelli, Francesco; Ferrucci, Luigi; Incalzi, Raffaele Antonelli
2016-01-01
Background Several formulas are available to estimate glomerular filtration rate (GFR) at the bedside. A decrease in GFR has been associated with poorer performance. We hypothesized that it is related to worsening disability as well. The aim of this study was to evaluate whether the Modification of Diet in Renal Disease formulas can predict worsening disability better than the classic Cockcroft-Gault formula or the measured creatinine clearance. Methods We studied 666 participants in the InCHIANTI study with 6 years of follow-up data. We evaluated whether directly measured creatinine clearance and GFR estimated using the Modification of Diet in Renal Disease and Cockcroft-Gault formulas predict new disability defined as the loss of ≥1 ADL over the 6-year follow-up. Results The mean age was 73.1 years (SD: 6.1), 57.7% were women. Fewer than 5% of participants were disabled at baseline. Eighty-one (12.2%) participants experienced a decline in activities of daily life score at follow-up. Declining GFR was associated with increasing risk of worsening disability (Mantel-Haenszel P < .001), with an increased steepness in the curve at GFR below 60 mL/min. The relative risks for worsening disability in people with GFR less than 60 mL/min/m were 3.19 (95% CI: 2.12–4.79) and 4.40 (95% CI: 2.80–6.94) using the Modification of Diet in Renal Disease and the Cockcroft-Gault equations, respectively. The corresponding figures obtained with measured creatinine clearance was 3.95 (95% CI: 2.60–6.01). After adjustment for potential confounders, however, these estimates were substantially reduced. Conclusion Estimation of renal function with the Cockcroft-Gault or Modification of Diet in Renal Disease formulas can help to identify elderly at risk of worsening disability. The mechanism by which reduced kidney function predicts disability should be further investigated. PMID:21450248
Cabrerizo-García, José Luis; Díez-Manglano, Jesús; García-Arilla, Ernesto; Revillo-Pinilla, Paz; Ramón-Puertas, José; Sebastián-Royo, Mariano
2015-01-06
The Modification of Diet in Renal Disease (MDRD) equation is recommended by most scientific societies to calculate the estimated glomerular filtration rate (GFR). Recently the group Chronic Kidney Disease Epidemiology Collaboration (CKP-EPI) has published a new, more precise and accurate equation. We have analyzed its behavior in a group of polypathological patients (PP) and compared it with the classic MDRD-4.version Multicenter, observational, descriptive and transversal study. We calculated GFR by MDRD-4 and CKD-EPI in 425 PP. Each stage was assigned according to the GFR: 1:>90; 2: 60-89; 3: 30-59; 4: 15-29; and 5 renal insufficiency, especially in older women. Copyright © 2013 Elsevier España, S.L.U. All rights reserved.
Generalized estimating equations
Hardin, James W
2002-01-01
Although powerful and flexible, the method of generalized linear models (GLM) is limited in its ability to accurately deal with longitudinal and clustered data. Developed specifically to accommodate these data types, the method of Generalized Estimating Equations (GEE) extends the GLM algorithm to accommodate the correlated data encountered in health research, social science, biology, and other related fields.Generalized Estimating Equations provides the first complete treatment of GEE methodology in all of its variations. After introducing the subject and reviewing GLM, the authors examine th
Generalized estimating equations
Hardin, James W
2013-01-01
Generalized Estimating Equations, Second Edition updates the best-selling previous edition, which has been the standard text on the subject since it was published a decade ago. Combining theory and application, the text provides readers with a comprehensive discussion of GEE and related models. Numerous examples are employed throughout the text, along with the software code used to create, run, and evaluate the models being examined. Stata is used as the primary software for running and displaying modeling output; associated R code is also given to allow R users to replicat
The normal renal size of Korean children. Radiologic estimation
Energy Technology Data Exchange (ETDEWEB)
Ko, Young Tae; Hyun, Jae Suk; Kim, Young Sun; Kim, Kyung Do [Chungang University College of Medicine, Chinju (Korea, Republic of)
1995-05-01
A nephropathy following urinary tract infection is usually referred to as renal scarring. The main radiologic features are an overall reduction in the size of the kidney, with coarse scar, deformity of calyxes and indentation of the surface. If adequately treated, the progressive renal scarring by urinary tract infection could be prevented. Therefore, the early radiologic detection of renal damage following urinary tract infection or vesicoureteral reflux is great importance for the evaluation of the pathogenesis of renal scarring and for the planning of the therapy. To evaluate the renal damage, we must have the normal data of the kidneys. Many reports discussed the renal size in normal children, but there are no reports in the Korean children. We estimate the renal length, width, several focal parenchymal thicknesses for renal size evaluation and segmental lumbar vertebral length at the intravenous paleography in the normal Korean children. And the linear equations are obtained by the regression analysis between the various renal parameters and segmental vertebral length. Thereafter we make out the nomogram by the obtained equations. The renal length and width are highly correlated to the segmental lumbar vertebral length than various renal parenchymal thicknesses. These results suggest that the renal length and width are reliable parameters for normal renal size evaluation in growing kidney. And then the obtained equations and nomograms might be useful in the diagnosis of parenchymal loss in early scarring and follow-up. (author)
Hermida-Cadahia, Esperanza F.; Lampon, Natalia
2012-01-01
Background. It has recently been reported that patient selection has a strong impact on the agreement between glomerular filtration rate (GFR) estimates from serum cystatin C and creatinine. The aim of our study was to evaluate the effect of creatinine production rate (CPR) on this subject. Material and methods. GFR was estimated from serum cystatin C and from creatinine using the 4- and 6-variable Modification of Diet in Renal Disease (MDRD), and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations in 50 healthy subjects, 43 patients with renal failure, 794 kidney and 104 liver transplant recipients, 61 patients with heart failure, 59 patients with biliary obstruction, and 113 critically ill patients. Results. In the 295 patients with impaired CPR ( 900 mg/24 h/1.73 m2), greater discordances than 40% between GFRMDRD4 and GFRcystatinC were observed in 8% of cases, between GFRMDRD6 and GFRcystatinC in 9%, and between GFRCKD-EPI and GFRcystatinC in 7% (in the major part of cases due to GFR overestimation from cystatin C). Conclusion. The main source of differences of more than 40% between GFR estimates from serum creatinine and cystatin C is a GFR overestimation in patients with low CPR and GFR underestimation in patients with high CPR by the creatinine-derived equations. PMID:22746300
Renal parameter estimates in unrestrained dogs
Rader, R. D.; Stevens, C. M.
1974-01-01
A mathematical formulation has been developed to describe the hemodynamic parameters of a conceptualized kidney model. The model was developed by considering regional pressure drops and regional storage capacities within the renal vasculature. Estimation of renal artery compliance, pre- and postglomerular resistance, and glomerular filtration pressure is feasible by considering mean levels and time derivatives of abdominal aortic pressure and renal artery flow. Changes in the smooth muscle tone of the renal vessels induced by exogenous angiotensin amide, acetylcholine, and by the anaesthetic agent halothane were estimated by use of the model. By employing totally implanted telemetry, the technique was applied on unrestrained dogs to measure renal resistive and compliant parameters while the dogs were being subjected to obedience training, to avoidance reaction, and to unrestrained caging.
[Methods for the estimation of the renal function].
Fontseré Baldellou, Néstor; Bonal I Bastons, Jordi; Romero González, Ramón
2007-10-13
The chronic kidney disease represents one of the pathologies with greater incidence and prevalence in the present sanitary systems. The ambulatory application of different methods that allow a suitable detection, monitoring and stratification of the renal functionalism is of crucial importance. On the basis of the vagueness obtained by means of the application of the serum creatinine, a set of predictive equations for the estimation of the glomerular filtration rate have been developed. Nevertheless, it is essential for the physician to know its limitations, in situations of normal renal function and hyperfiltration, certain associate pathologies and extreme situations of nutritional status and age. In these cases, the application of the isotopic techniques for the calculation of the renal function is more recommendable.
Observability Estimate for Stochastic Schroedinger Equations
2012-01-01
In this paper, we establish a boundary observability estimate for stochastic Schr\\"{o}dinger equations by means of the global Carleman estimate. Our Carleman estimate is based on a new fundamental identity for a stochastic Schr\\"{o}dinger-like operator. Applications to the state observation problem for semilinear stochastic Schr\\"{o}dinger equations and the unique continuation problem for stochastic Schr\\"{o}dinger equations are also addressed.
Glomerular Filtration Rate Estimation in Renal and Non-Renal Solid Organ Transplantation
DEFF Research Database (Denmark)
Hornum, Mads; Feldt-Rasmussen, Bo
2017-01-01
or estimates of renal function in these patients, in order to accurately and safely dose immunosuppressive medication and perform and adjust the treatment and prophylaxis of renal dysfunction. This is a short overview and discussion of relevant studies and possible caveats of estimated glomerular filtration...... rate methods for use in renal and non-renal TX....
Matsushita, K.; Mahmoodi, B.K.; Woodward, M.; Emberson, J.R.; Jafar, T.H.; Jee, S.H.; Polkinghorne, K.R.; Shankar, A.; Smith, D.H.; Tonelli, M.; Warnock, D.G.; Wen, C.P.; Coresh, J.; Gansevoort, R.T.; Hemmelgarn, B.R.; Levey, A.S.; Wetzels, J.F.
2012-01-01
CONTEXT: The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation more accurately estimates glomerular filtration rate (GFR) than the Modification of Diet in Renal Disease (MDRD) Study equation using the same variables, especially at higher GFR, but definitive evidence of its risk
SPACE-TIME ESTIMATE TO HEAT EQUATION
Institute of Scientific and Technical Information of China (English)
2007-01-01
In this article, we prove the Strichartz type estimate for the solutions of linear heat equation with initial data in Hardy space H1(Rd). As an application, we obtain the full space-time estimate to the solutions of heat equation with initial data in LP(Rd) for 1＜p＜∞.
Equating accelerometer estimates among youth
DEFF Research Database (Denmark)
Brazendale, Keith; Beets, Michael W; Bornstein, Daniel B;
2016-01-01
OBJECTIVES: Different accelerometer cutpoints used by different researchers often yields vastly different estimates of moderate-to-vigorous intensity physical activity (MVPA). This is recognized as cutpoint non-equivalence (CNE), which reduces the ability to accurately compare youth MVPA across s...
Estimating the Rate of Occurrence of Renal Stones in Astronauts
Myers, J.; Goodenow, D.; Gokoglu, S.; Kassemi, M.
2016-01-01
Changes in urine chemistry, during and post flight, potentially increases the risk of renal stones in astronauts. Although much is known about the effects of space flight on urine chemistry, no inflight incidence of renal stones in US astronauts exists and the question "How much does this risk change with space flight?" remains difficult to accurately quantify. In this discussion, we tackle this question utilizing a combination of deterministic and probabilistic modeling that implements the physics behind free stone growth and agglomeration, speciation of urine chemistry and published observations of population renal stone incidences to estimate changes in the rate of renal stone presentation. The modeling process utilizes a Population Balance Equation based model developed in the companion IWS abstract by Kassemi et al. (2016) to evaluate the maximum growth and agglomeration potential from a specified set of urine chemistry values. Changes in renal stone occurrence rates are obtained from this model in a probabilistic simulation that interrogates the range of possible urine chemistries using Monte Carlo techniques. Subsequently, each randomly sampled urine chemistry undergoes speciation analysis using the well-established Joint Expert Speciation System (JESS) code to calculate critical values, such as ionic strength and relative supersaturation. The Kassemi model utilizes this information to predict the mean and maximum stone size. We close the assessment loop by using a transfer function that estimates the rate of stone formation from combining the relative supersaturation and both the mean and maximum free stone growth sizes. The transfer function is established by a simulation analysis which combines population stone formation rates and Poisson regression. Training this transfer function requires using the output of the aforementioned assessment steps with inputs from known non-stone-former and known stone-former urine chemistries. Established in a Monte Carlo
Efficient Estimating Functions for Stochastic Differential Equations
DEFF Research Database (Denmark)
Jakobsen, Nina Munkholt
The overall topic of this thesis is approximate martingale estimating function-based estimationfor solutions of stochastic differential equations, sampled at high frequency. Focuslies on the asymptotic properties of the estimators. The first part of the thesis deals with diffusions observed over...
Andro, M; Estivin, S; Comps, E; Gentric, A
2011-11-01
Assessment of renal function is essential in the management of hospitalised patients, particularly in geriatric practice. Impairment of renal function is common in the elderly, aged of 80 years and over, and should be taken into account before prescribing drugs eliminated through the kidneys or performing investigations requiring iodine injection. Renal failure is also a predictor of mortality. In clinical practice, creatinine-based equations are recommended to assess kidney function. The most widely used equations are the Cockroft and Gault (CG) and the simplified Modification of diet in renal disease (MDRD) formulas. The former estimates the clearance of creatinine in millilitres per minute, the latter estimates the glomerular filtration rate in millilitres per minute per 1.73 m(2). In 2002, the French high authority for health recommended the use of the CG formula, but no recommendation was given for the elderly. In the literature, no study has compared CG and MDRD formulas with a reference method in this very old population. In the octogenarians, two studies have compared these formulas with the creatinine clearance calculated on the basis of a 24-hour urine collection and four studies have compared the formulas head to head. All these studies showed that the results obtained with the MDRD formula are higher from 10 to 30 mL/min/1.73 m(2) than the results obtained with the CG formula. Studies simulating drug prescription showed that the use of the MDRD formula would lead to a risk of drug over dosage in 20 to 36% of the elderly. Also, two studies have suggested that only creatinine clearance measured by the CG formula is a predictor of mortality in the very old population. In conclusion, in the octogenarian, none of these two formulas is ideal. However, based on the results of studies targeted to this elderly population, the best solution seems to be the use of the CG formula expecting new methods of evaluation of renal function.
Stagewise generalized estimating equations with grouped variables.
Vaughan, Gregory; Aseltine, Robert; Chen, Kun; Yan, Jun
2017-02-13
Forward stagewise estimation is a revived slow-brewing approach for model building that is particularly attractive in dealing with complex data structures for both its computational efficiency and its intrinsic connections with penalized estimation. Under the framework of generalized estimating equations, we study general stagewise estimation approaches that can handle clustered data and non-Gaussian/non-linear models in the presence of prior variable grouping structure. As the grouping structure is often not ideal in that even the important groups may contain irrelevant variables, the key is to simultaneously conduct group selection and within-group variable selection, that is, bi-level selection. We propose two approaches to address the challenge. The first is a bi-level stagewise estimating equations (BiSEE) approach, which is shown to correspond to the sparse group lasso penalized regression. The second is a hierarchical stagewise estimating equations (HiSEE) approach to handle more general hierarchical grouping structure, in which each stagewise estimation step itself is executed as a hierarchical selection process based on the grouping structure. Simulation studies show that BiSEE and HiSEE yield competitive model selection and predictive performance compared to existing approaches. We apply the proposed approaches to study the association between the suicide-related hospitalization rates of the 15-19 age group and the characteristics of the school districts in the State of Connecticut.
Integrability Estimates for Gaussian Rough Differential Equations
Cass, Thomas; Lyons, Terry
2011-01-01
We derive explicit tail-estimates for the Jacobian of the solution flow of stochastic differential equations driven by Gaussian rough paths. In particular, we deduce that the Jacobian has finite moments of all order for a wide class of Gaussian process including fractional Brownian motion with Hurst parameter H>1/4. We remark on the relevance of such estimates to a number of significant open problems.
Parameter estimation in stochastic differential equations
Bishwal, Jaya P N
2008-01-01
Parameter estimation in stochastic differential equations and stochastic partial differential equations is the science, art and technology of modelling complex phenomena and making beautiful decisions. The subject has attracted researchers from several areas of mathematics and other related fields like economics and finance. This volume presents the estimation of the unknown parameters in the corresponding continuous models based on continuous and discrete observations and examines extensively maximum likelihood, minimum contrast and Bayesian methods. Useful because of the current availability of high frequency data is the study of refined asymptotic properties of several estimators when the observation time length is large and the observation time interval is small. Also space time white noise driven models, useful for spatial data, and more sophisticated non-Markovian and non-semimartingale models like fractional diffusions that model the long memory phenomena are examined in this volume.
Estimation of feline renal volume using computed tomography and ultrasound.
Tyson, Reid; Logsdon, Stacy A; Werre, Stephen R; Daniel, Gregory B
2013-01-01
Renal volume estimation is an important parameter for clinical evaluation of kidneys and research applications. A time efficient, repeatable, and accurate method for volume estimation is required. The purpose of this study was to describe the accuracy of ultrasound and computed tomography (CT) for estimating feline renal volume. Standardized ultrasound and CT scans were acquired for kidneys of 12 cadaver cats, in situ. Ultrasound and CT multiplanar reconstructions were used to record renal length measurements that were then used to calculate volume using the prolate ellipsoid formula for volume estimation. In addition, CT studies were reconstructed at 1 mm, 5 mm, and 1 cm, and transferred to a workstation where the renal volume was calculated using the voxel count method (hand drawn regions of interest). The reference standard kidney volume was then determined ex vivo using water displacement with the Archimedes' principle. Ultrasound measurement of renal length accounted for approximately 87% of the variability in renal volume for the study population. The prolate ellipsoid formula exhibited proportional bias and underestimated renal volume by a median of 18.9%. Computed tomography volume estimates using the voxel count method with hand-traced regions of interest provided the most accurate results, with increasing accuracy for smaller voxel sizes in grossly normal kidneys (-10.1 to 0.6%). Findings from this study supported the use of CT and the voxel count method for estimating feline renal volume in future clinical and research studies.
GFR Estimating Equations and Liver Disease.
Beben, Tomasz; Rifkin, Dena E
2015-09-01
It is important to accurately assess the glomerular filtration rate (GFR) of patients with liver disease to deliver care and allocate organs for transplantation in a way that improves outcomes. The most commonly used methods to estimate GFR in this population are based on creatinine, which is biased by these patients' low creatinine production and potentially by elevated serum bilirubin and decreased albumin levels. None of the creatinine-based estimated glomerular filtration rate (eGFR) equations have been specifically modified for a population with liver disease, and even measurement of a 24-hour creatinine clearance has limitations. In liver disease, all creatinine-based estimates of GFR overestimate gold standard-measured GFR, and the degree of overestimation is highest at lower measured GFR values and in more severe liver disease. Cystatin C-based eGFR has shown promise in general population studies by demonstrating less bias than creatinine-based eGFR and improved association with clinically important outcomes, but results in the liver disease population have been mixed, and further studies are necessary. Ultimately, specific eGFR equations for liver disease or novel methods for estimating GFR may be necessary. However, for now, the limitations of currently available methods need to be appreciated to understand kidney function in liver disease.
Equations of States in Singular Statistical Estimation
Watanabe, Sumio
2007-01-01
Learning machines which have hierarchical structures or hidden variables are singular statistical models because they are nonidentifiable and their Fisher information matrices are singular. In singular statistical models, neither the Bayes a posteriori distribution converges to the normal distribution nor the maximum likelihood estimator satisfies asymptotic normality. This is the main reason why it has been difficult to predict their generalization performances from trained states. In this paper, we study four errors, (1) Bayes generalization error, (2) Bayes training error, (3) Gibbs generalization error, and (4) Gibbs training error, and prove that there are mathematical relations among these errors. The formulas proved in this paper are equations of states in statistical estimation because they hold for any true distribution, any parametric model, and any a priori distribution. Also we show that Bayes and Gibbs generalization errors are estimated by Bayes and Gibbs training errors, and propose widely appl...
Suzuki, Ryohei; Ohtsu, Fumiko; Goto, Nobuyuki
2015-01-01
The purpose of this study was to develop and validate estimate equations for preventing adverse drug reactions (ADRs). We conducted five case-control studies to identify individual risk factors and subjective symptoms associated with the following five ADRs: drug-induced ischemic heart disease; renal damage; muscle disorder; interstitial pneumonia; and leucopenia. We performed logistic regression analysis and obtained eight regression equations for each ADR. We converted these to ADR estimate equations for predicting the likelihood of ADRs. We randomly selected 50 cases with non-individual ADRs from the Case Reports of Adverse Drug Reactions and Poisoning Information System (CARPIS) database of over 65000 case reports of ADRs, and assigned these cases to a validation case group. We then calculated the predictive probability for 50 cases using the eight estimate equations for each ADR. The highest probability for each ADR was set as the probability of each ADR. If the probability was over 50%, the case was interpreted as ADR-positive. We calculated and evaluated the sensitivity, specificity, and positive likelihood ratio of this system. Sensitivity of the estimate equations for muscle disorder and interstitial pneumonia were ≥90%. Specificity and positive likelihood ratios of estimate equations for renal damage, interstitial pneumonia and leucopenia were ≥80% and ≥5, respectively. Our estimate equations thus showed high validity, and are therefore helpful for the prevention or early detection of ADRs.
Montañés Bermúdez, R; Gràcia Garcia, S; Fraga Rodríguez, G M; Escribano Subias, J; Diez de Los Ríos Carrasco, M J; Alonso Melgar, A; García Nieto, V
2014-05-01
The appearance of the K/DOQI guidelines in 2002 on the definition, evaluation and staging of chronic kidney disease (CKD) have led to a major change in how to assess renal function in adults and children. These guidelines, recently updated, recommended that the study of renal function is based, not only on measuring the serum creatinine concentration, but this must be accompanied by the estimation of glomerular filtration rate (GFR) obtained by an equation. However, the implementation of this recommendation in the clinical laboratory reports in the paediatric population has been negligible. Numerous studies have appeared in recent years on the importance of screening and monitoring of patients with CKD, the emergence of new equations for estimating GFR, and advances in clinical laboratories regarding the methods for measuring plasma creatinine and cystatin C, determined by the collaboration between the departments of paediatrics and clinical laboratories to establish recommendations based on the best scientific evidence on the use of equations to estimate GFR in this population. The purpose of this document is to provide recommendations on the evaluation of renal function and the use of equations to estimate GFR in children from birth to 18 years of age. The recipients of these recommendations are paediatricians, nephrologists, clinical biochemistry, clinical analysts, and all health professionals involved in the study and evaluation of renal function in this group of patients.
Regularized Semiparametric Estimation for Ordinary Differential Equations.
Li, Yun; Zhu, Ji; Wang, Naisyin
2015-07-01
Ordinary differential equations (ODEs) are widely used in modeling dynamic systems and have ample applications in the fields of physics, engineering, economics and biological sciences. The ODE parameters often possess physiological meanings and can help scientists gain better understanding of the system. One key interest is thus to well estimate these parameters. Ideally, constant parameters are preferred due to their easy interpretation. In reality, however, constant parameters can be too restrictive such that even after incorporating error terms, there could still be unknown sources of disturbance that lead to poor agreement between observed data and the estimated ODE system. In this paper, we address this issue and accommodate short-term interferences by allowing parameters to vary with time. We propose a new regularized estimation procedure on the time-varying parameters of an ODE system so that these parameters could change with time during transitions but remain constants within stable stages. We found, through simulation studies, that the proposed method performs well and tends to have less variation in comparison to the non-regularized approach. On the theoretical front, we derive finite-sample estimation error bounds for the proposed method. Applications of the proposed method to modeling the hare-lynx relationship and the measles incidence dynamic in Ontario, Canada lead to satisfactory and meaningful results.
Parameter Estimation of Partial Differential Equation Models
Xun, Xiaolei
2013-09-01
Partial differential equation (PDE) models are commonly used to model complex dynamic systems in applied sciences such as biology and finance. The forms of these PDE models are usually proposed by experts based on their prior knowledge and understanding of the dynamic system. Parameters in PDE models often have interesting scientific interpretations, but their values are often unknown and need to be estimated from the measurements of the dynamic system in the presence of measurement errors. Most PDEs used in practice have no analytic solutions, and can only be solved with numerical methods. Currently, methods for estimating PDE parameters require repeatedly solving PDEs numerically under thousands of candidate parameter values, and thus the computational load is high. In this article, we propose two methods to estimate parameters in PDE models: a parameter cascading method and a Bayesian approach. In both methods, the underlying dynamic process modeled with the PDE model is represented via basis function expansion. For the parameter cascading method, we develop two nested levels of optimization to estimate the PDE parameters. For the Bayesian method, we develop a joint model for data and the PDE and develop a novel hierarchical model allowing us to employ Markov chain Monte Carlo (MCMC) techniques to make posterior inference. Simulation studies show that the Bayesian method and parameter cascading method are comparable, and both outperform other available methods in terms of estimation accuracy. The two methods are demonstrated by estimating parameters in a PDE model from long-range infrared light detection and ranging data. Supplementary materials for this article are available online. © 2013 American Statistical Association.
Cystatin C enhances GFR estimating Equations in Kidney Transplant Recipients
Kukla, Aleksandra; Issa, Naim; Jackson, Scott; Spong, Richard; Foster, Meredith C.; Matas, Arthur J.; Mauer, Michael S.; Eckfeldt, John H.; Ibrahim, Hassan N.
2014-01-01
Background The glomerular filtration rate (GFR) estimating equation incorporating both cystatin C and creatinine perform better than those using creatinine or cystatin C alone in patients with reduced GFR. Whether this equation performs well in kidney transplant recipients cross-sectionally, and more importantly, over time has not been addressed. Methods We analyzed four GFR estimating equations in participants of the Angiotensin II Blockade for Chronic Allograft Nephropathy Trial (NCT 00067990): Chronic Kidney Disease Epidemiology Collaboration equations based on serum cystatin C and creatinine (eGFR (CKD-EPI-Creat+CysC)), cystatin C alone (eGFR (CKD-EPI-CysC)), creatinine alone (eGFR (CKD-EPI-Creat)) and the Modification of Diet in Renal Disease study equation (eGFR(MDRD)). Iothalamate GFR served as a standard (mGFR). Results mGFR, serum creatinine, and cystatin C shortly after transplant were 56.1 ± 17.0 mL/min/1.73 m2, 1.2 ± 0.4 mg/dL, and 1.2 ± 0.3 mg/L respectively. eGFR (CKD-EPI-Creat+CysC) was most precise (R2=0.50) but slightly more biased than eGFR (MDRD); 9.0 ± 12.7 ml/min/1.73m2 vs. 6.4 ± 15.8 ml/min/1.73m2, respectively. This improved precision was most evident in recipients with mGFR >60 ml/min/1.73m2. For relative accuracy, eGFR (MDRD) and eGFR (CKD-EPI-Creat+CysC) had the highest percentage of estimates falling within 30% of mGFR; 75.8% and 68.9%, respectively. Longitudinally, equations incorporating cystatin C most closely paralleled the change in mGFR. Conclusion eGFR (CKD-EPI-Creat+CysC) is more precise and reflects GFR change over time reasonably well. eGFR (MDRD) had superior performance in recipients with mGFR between 30–60 ml/min/1.73m2. PMID:24457184
Renal parenchyma thickness: a rapid estimation of renal function on computed tomography
Energy Technology Data Exchange (ETDEWEB)
Kaplon, Daniel M.; Lasser, Michael S.; Sigman, Mark; Haleblian, George E.; Pareek, Gyan [The Warren Alpert School of Medicine of Brown University, Providence, RI (United States). Dept. pf Surgery. Section of Minimally Invasive Urologic Surgery], e-mail: kaplonda@gmail.com
2009-01-15
Purpose: To define the relationship between renal parenchyma thickness (RPT) on computed tomography and renal function on nuclear renography in chronically obstructed renal units (ORUs) and to define a minimal thickness ratio associated with adequate function. Materials and Methods: Twenty-eight consecutive patients undergoing both nuclear renography and CT during a six-month period between 2004 and 2006 were included. All patients that had a diagnosis of unilateral obstruction were included for analysis. RPT was measured in the following manner: The parenchyma thickness at three discrete levels of each kidney was measured using calipers on a CT workstation. The mean of these three measurements was defined as RPT. The renal parenchyma thickness ratio of the ORUs and non-obstructed renal unit (NORUs) was calculated and this was compared to the observed function on Mag-3 lasix Renogram. Results: A total of 28 patients were evaluated. Mean parenchyma thickness was 1.82 cm and 2.25 cm in the ORUs and NORUs, respectively. The mean relative renal function of ORUs was 39%. Linear regression analysis comparing renogram function to RPT ratio revealed a correlation coefficient of 0.48 (p < 0.001). The linear regression equation was computed as Renal Function = 0.48 + 0.80{sup *} RPT ratio. A thickness ratio of 0.68 correlated with 20% renal function. Conclusion: RPT on computed tomography appears to be a powerful predictor of relative renal function in ORUs. Assessment of RPT is a useful and readily available clinical tool for surgical decision making (renal salvage therapy versus nephrectomy) in patients with ORUs. (author)
Renal parenchyma thickness: a rapid estimation of renal function on computed tomography
Directory of Open Access Journals (Sweden)
Daniel M. Kaplon
2009-02-01
Full Text Available Purpose: To define the relationship between renal parenchyma thickness (RPT on computed tomography and renal function on nuclear renography in chronically obstructed renal units (ORUs and to define a minimal thickness ratio associated with adequate function. Materials and Methods: Twenty-eight consecutive patients undergoing both nuclear renography and CT during a six-month period between 2004 and 2006 were included. All patients that had a diagnosis of unilateral obstruction were included for analysis. RPT was measured in the following manner: The parenchyma thickness at three discrete levels of each kidney was measured using calipers on a CT workstation. The mean of these three measurements was defined as RPT. The renal parenchyma thickness ratio of the ORUs and non-obstructed renal unit (NORUs was calculated and this was compared to the observed function on Mag-3 lasix Renogram. Results: A total of 28 patients were evaluated. Mean parenchyma thickness was 1.82 cm and 2.25 cm in the ORUs and NORUs, respectively. The mean relative renal function of ORUs was 39%. Linear regression analysis comparing renogram function to RPT ratio revealed a correlation coefficient of 0.48 (p < 0.001. The linear regression equation was computed as Renal Function = 0.48 + 0.80 * RPT ratio. A thickness ratio of 0.68 correlated with 20% renal function. Conclusion: RPT on computed tomography appears to be a powerful predictor of relative renal function in ORUs. Assessment of RPT is a useful and readily available clinical tool for surgical decision making (renal salvage therapy versus nephrectomy in patients with ORUs.
Precise renal artery segmentation for estimation of renal vascular dominant regions
Wang, Chenglong; Kagajo, Mitsuru; Nakamura, Yoshihiko; Oda, Masahiro; Yoshino, Yasushi; Yamamoto, Tokunori; Mori, Kensaku
2016-03-01
This paper presents a novel renal artery segmentation method combining graph-cut and template-based tracking methods and its application to estimation of renal vascular dominant region. For the purpose of giving a computer assisted diagnose for kidney surgery planning, it is important to obtain the correct topological structures of renal artery for estimation of renal vascular dominant regions. Renal artery has a low contrast, and its precise extraction is a difficult task. Previous method utilizing vesselness measure based on Hessian analysis, still cannot extract the tiny blood vessels in low-contrast area. Although model-based methods including superellipsoid model or cylindrical intensity model are low-contrast sensitive to the tiny blood vessels, problems including over-segmentation and poor bifurcations detection still remain. In this paper, we propose a novel blood vessel segmentation method combining a new Hessian-based graph-cut and template modeling tracking method. Firstly, graph-cut algorithm is utilized to obtain the rough segmentation result. Then template model tracking method is utilized to improve the accuracy of tiny blood vessel segmentation result. Rough segmentation utilizing graph-cut solves the bifurcations detection problem effectively. Precise segmentation utilizing template model tracking focuses on the segmentation of tiny blood vessels. By combining these two approaches, our proposed method segmented 70% of the renal artery of 1mm in diameter or larger. In addition, we demonstrate such precise segmentation can contribute to divide renal regions into a set of blood vessel dominant regions utilizing Voronoi diagram method.
Observability estimate and state observation problems for stochastic hyperbolic equations
2013-01-01
In this paper, we derive a boundary and an internal observability inequality for stochastic hyperbolic equations with nonsmooth lower order terms. The required inequalities are obtained by global Carleman estimate for stochastic hyperbolic equations. By these inequalities, we study a state observation problem for stochastic hyperbolic equations. As a consequence, we also establish a unique continuation property for stochastic hyperbolic equations.
Nonparametric Bayesian drift estimation for multidimensional stochastic differential equations
Gugushvili, S.; Spreij, P.
2014-01-01
We consider nonparametric Bayesian estimation of the drift coefficient of a multidimensional stochastic differential equation from discrete-time observations on the solution of this equation. Under suitable regularity conditions, we establish posterior consistency in this context.
Carleman Estimates for Parabolic Equations with Nonhomogeneous Boundary Conditions
Institute of Scientific and Technical Information of China (English)
Oleg Yu IMANUVILOV; Jean Pierre PUEL; Masahiro YAMAMOTO
2009-01-01
The authors prove a new Carleman estimate for general linear second order parabolic equation with nonhomogeneous boundary conditions.On the basis of this estimate,improved Carleman estimates for the Stokes system and for a system of parabolic equations with a penalty term are obtained.This system can be viewed as an approximation of the Stokes system.
Carleman and Observability Estimates for Stochastic Wave Equations
2007-01-01
Based on a fundamental identity for stochastic hyperbolic-like operators, we derive in this paper a global Carleman estimate (with singular weight function) for stochastic wave equations. This leads to an observability estimate for stochastic wave equations with non-smooth lower order terms. Moreover, the observability constant is estimated by an explicit function of the norm of the involved coefficients in the equation.
Estimation and relevance of depth correction in paediatric renal studies
Energy Technology Data Exchange (ETDEWEB)
Lythgoe, M.F.; Gradwell, M.J.; Evans, K.; Gordon, I. [Department of Radiology, Great Ormond Street Hospital for Children NHS Trust, London (United Kingdom)
1998-02-01
Measurement of absolute renal function by gamma camera techniques requires knowledge of kidney depth to correct for soft tissue attenuation, there is debate about the need to take depth into account when only relative renal function is estimated. The aim of this study was to derive a formula for renal depth in children and to assess the importance of depth correction when relative renal function is assessed with dimercaptosuccinic acid (DMSA) on the gamma camera. In this study, kidney depths were derived from measurements on abdominal computerised tomography (CT) images in 57 children in the supine position with two normally located kidneys. Using best-subset regression analysis, one formula for both left and right kidney depth (KD, cm) was developed based on the easily measured parameters of height (H, cm) and body weight (W, kg). The inclusion of extra variables was found to significantly improve the model compared with a model using weight alone (P<0.005). A second group of 19 children who underwent technetium-99m DMSA scans, had differential function estimated from both anterior and posterior views and the geometric mean method. The mean difference in differential renal function calculated by the geometric mean method versus the posterior image was only 1.2%. In conclusion, we present a new formula for the estimation of paediatric kidney depth for the absolute quantitation of kidney uptake. Further, for normally located kidneys it appears unnecessary to use the geometric mean method or to correct for individual renal depth when calculating differential function. (orig.) With 2 figs., 1 tab., 22 refs.
An Internal Observability Estimate for Stochastic Hyperbolic Equations
2015-01-01
This paper is addressed to establishing an internal observability estimate for some linear stochastic hyperbolic equations. The key is to establish a new global Carleman estimate for forward stochastic hyperbolic equations in the $L^2$-space. Different from the deterministic case, a delicate analysis of the adaptedness for some stochastic processes is required in the stochastic setting.
Equations for filling factor estimation in opal matrix
Abrarov, S M; Kim, T W
2005-01-01
We consider two equations for the filling factor estimation of infiltrated zinc oxide (ZnO) in silica (SiO2) opal and gallium nitride in ZnO opal. The first equation is based on the effective medium approximation, while the second one - on Maxwell-Garnett approximation. The comparison between two filling factors shows that both equations can be equally used for the estimation of the quantity of infiltrated nanocrystals inside opal matrix.
Refined Error Estimates for the Riccati Equation with Applications to the Angular Teukolsky Equation
Finster, Felix
2013-01-01
We derive refined rigorous error estimates for approximate solutions of Sturm-Liouville and Riccati equations with real or complex potentials. The approximate solutions include WKB approximations, Airy and parabolic cylinder functions, and certain Bessel functions. Our estimates are applied to solutions of the angular Teukolsky equation with a complex aspherical parameter in a rotating black hole Kerr geometry.
Smoothing and Decay Estimates for Nonlinear Diffusion Equations Equations of Porous Medium Type
Vázquez, Juan Luis
2006-01-01
This text is concerned with the quantitative aspects of the theory of nonlinear diffusion equations; equations which can be seen as nonlinear variations of the classical heat equation. They appear as mathematical models in different branches of Physics, Chemistry, Biology, and Engineering, and are also relevant in differential geometry and relativistic physics. Much of the modern theory of such equations is based on estimates and functional analysis.Concentrating on a class of equations with nonlinearities of power type that lead to degenerate or singular parabolicity ("equations of porou
Lp estimates for-(e)-equation on generalized complex ellipsoids
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
The estimate of a holomorphic supporting function for the generalized complex ellipsoid in is Cn given, This domain is not decoupled. By using this estimate, the best possible Lp estimates for the -(e)-equation and some results of function theory on generalized complex ellipsoids are proved.
A Note on Structural Equation Modeling Estimates of Reliability
Yang, Yanyun; Green, Samuel B.
2010-01-01
Reliability can be estimated using structural equation modeling (SEM). Two potential problems with this approach are that estimates may be unstable with small sample sizes and biased with misspecified models. A Monte Carlo study was conducted to investigate the quality of SEM estimates of reliability by themselves and relative to coefficient…
The Gomez' equations and renal hemodynamic function in kidney disease research.
Bjornstad, Petter; Škrtić, Marko; Lytvyn, Yuliya; Maahs, David M; Johnson, Richard J; Cherney, David Z I
2016-09-07
Diabetic kidney disease (DKD) remains the leading cause of end-stage renal disease. A major challenge in preventing DKD is the difficulty in identifying high-risk patients at an early, pre-clinical stage. Albuminuria and eGFR as measures of renal function in DKD research and clinical practice are limited by regression of one-third of patients with microalbuminuria to normoalbuminuria and eGFR is biased and imprecise in the normal-elevated range. Moreover, existing methods that are used to assess renal function do not give detailed insight into the location of the renal hemodynamic effects of pharmacological agents at the segmental level. To gain additional information about the intrarenal circulation in-vivo in humans, mathematical equations were developed by Gomez et al in the 1950s. These equations used measurements of GFR, renal blood flow (RBF), effective renal plasma flow (ERPF), renal vascular resistance (RVR), hematocrit and serum protein to calculate afferent and efferent arteriolar resistances, glomerular hydrostatic pressure and filtration pressure. Although indirect and based on physiological assumptions, these techniques have the potential to improve researchers' ability to identify early pre-clinical changes in renal hemodynamic function in patients with a variety of conditions including DKD, thereby offering tremendous potential in mechanistic human research studies. In this review, we focus on the application of Gomez' equations and summarize the potential and limitations of this technique in DKD research. We also summarize illustrative data derived from Gomez' equations in patients with type 1 (T1D) and type 2 diabetes (T2D) and hypertension.
Toward a universal equation to estimate postmortem interval.
Maile, Amy E; Inoue, Christopher G; Barksdale, Larry E; Carter, David O
2017-03-01
Estimating postmortem interval is an important goal in medicolegal death investigations. Although several methods have been developed to achieve this goal, many of these require significant time and advanced expertise to generate a reliable estimate. Unfortunately these techniques do not provide much insight during the early stages of an investigation when critical decisions must be made regarding the allocation of investigative resources. An equation was recently developed to address this problem: provide a preliminary estimate of postmortem interval to initiate an investigation while more advanced techniques are conducted. To evaluate this equation, we used it to estimate postmortem interval at multiple indoor death scenes with known PMI in Nebraska and Hawai'i. This equation allowed us to accurately estimate PMI at 15 of 19 (79%) indoor death scenes. In Nebraska, this equation was accurate at 100% of the scenes. In Hawai'i, this equation was accurate at 60% of the scenes. All inaccurate estimates of postmortem interval were associated with at least 20% mass loss and a postmortem interval of ≥4 days. Although this equation was accurate at the majority of the death scenes attended, we conclude that more research is warranted, particularly the effect of climate on decomposition and the investigators' ability to accurately estimate soft tissue mass loss.
ACCURATE ESTIMATES OF CHARACTERISTIC EXPONENTS FOR SECOND ORDER DIFFERENTIAL EQUATION
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
In this paper, a second order linear differential equation is considered, and an accurate estimate method of characteristic exponent for it is presented. Finally, we give some examples to verify the feasibility of our result.
Clinical Usefulness of a New Equation for Estimating Body Fat
Gomez-Ambrosi, J.; De Silva, C.; Catalan, V.; Rodriguez, A.; Galofre, J.C. (Juan Carlos); Escalada, J.; Valenti, V; Rotellar, F. (Fernando); Romero, S.; Ramirez, B.; J. Salvador; Frühbeck, G.
2012-01-01
OBJECTIVE: To assess the predictive capacity of a recently described equation that we have termed CUN-BAE (Clínica Universidad de Navarra-Body Adiposity Estimator) based on BMI, sex, and age for estimating body fat percentage (BF%) and to study its clinical usefulness. RESEARCH DESIGN AND METHODS: We conducted a comparison study of the developed equation with many other anthropometric indices regarding its correlation with actual BF% in a large cohort of 6,510 white subjects from b...
Directory of Open Access Journals (Sweden)
Ling-I Chen
Full Text Available Estimated glomerular filtration rate (eGFR using the Modification of Diet in Renal Disease (MDRD study or the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI equations may not be accurate for Asians; thus, we developed modified eGFR equations for Taiwanese adults.This cross-sectional study compared the Taiwanese eGFR equations, the MDRD study, and the CKD-EPI equations with inulin clearance (Cin. A total of 695 adults including 259 healthy volunteers and 436 CKD patients were recruited. Participants from the Kaohsiung Medical University Hospital were used as the development set (N = 556 to develop the Taiwanese eGFR equations, whereas participants from the National Taiwan University Hospital were used as the validation set (N = 139 for external validation.The Taiwanese eGFR equations were developed by using the extended Bland-Altman plot in the development set. The Taiwanese MDRD equation was 1.309 × MDRD0.912, Taiwanese CKD-EPI was 1.262×CKD-EPI0.914 and Taiwanese four-level CKD-EPI was 1.205 × four-level CKD-EPI0.914. In the validation set, the Taiwanese equations had the lowest bias, the Taiwanese equations and the Japanese CKD-EPI equation had the lowest RMSE, whereas the Taiwanese and the Japanese equations had the best precision and the highest P30 among all equations. However, the Taiwanese MDRD equation had higher concordance correlation than did the Taiwanese CKD-EPI, the Taiwanese four-level CKD-EPI and the Japanese equations. Moreover, only the Taiwanese equations had no proportional bias among all of the equations. Finally, the Taiwanese MDRD equation had the best diagnostic performance in terms of ordinal logistic regression among all of the equations.The Taiwanese MDRD equation is better than the MDRD, CKD-EPI, Japanese, Asian, Thai, Taiwanese CKD-EPI, and Taiwanese four-level CKD-EPI equations for Taiwanese adults.
Equation of motion for estimation fidelity of monitored oscillating qubits
Bassa, Humairah; Konrad, Thomas; Diósi, Lajos; Uys, Hermann
2017-08-01
We study the convergence properties of state estimates of an oscillating qubit being monitored by a sequence of discrete, unsharp measurements. Our method derives a differential equation determining the evolution of the estimation fidelity from a single incremental step. If the oscillation frequency Ω is precisely known, the estimation fidelity converges exponentially fast to unity. For imprecise knowledge of Ω we derive the asymptotic estimation fidelity.
Estimating equations for biomarker based exposure estimation under non-steady-state conditions.
Bartell, Scott M; Johnson, Wesley O
2011-06-13
Unrealistic steady-state assumptions are often used to estimate toxicant exposure rates from biomarkers. A biomarker may instead be modeled as a weighted sum of historical time-varying exposures. Estimating equations are derived for a zero-inflated gamma distribution for daily exposures with a known exposure frequency. Simulation studies suggest that the estimating equations can provide accurate estimates of exposure magnitude at any reasonable sample size, and reasonable estimates of the exposure variance at larger sample sizes.
[Estimate of the needs in renal transplantation in Morocco].
Boly, Ahmadou; El Hassane Trabelsi, Mohamed; Ramdani, Benyounes; Bayahia, Rabea; Benghanem Gharbi, Mohamed; Boucher, Stéphanie; El Berri, Hicham; Nejjari, Chakib; Couchoud, Cécile
2014-12-01
Kidney transplantation is still underdeveloped in Morocco. In order to anticipate needs and discuss a possible reorganization of the provision of care, an estimate of the number of patients who would benefit from kidney transplant was conducted. This study was done in two steps. During the first step, based on the French renal replacement therapy registry (Rein), we develop a prediction score based on the likelihood of being treated by an autonomous dialysis (hemodialysis in self-care unit or peritoneal dialysis non-assisted by a nurse) and be registered on the national kidney transplant waiting list. During the second step, we apply this score to the data of the registry Magredial (Moroccan registry of renal replacement therapy, deployed in seven regions). Twelve parameters were related to autonomy and registration on the waiting list. Each of these parameters has been assigned a weight. Each patient was assigned a number of points, sum of different weights. By retaining a threshold of 21 points (80% specificity), 2260 subjects (57%) had a score less than or equal to this threshold in Magredial. With a number of patients on dialysis in Morocco estimated to 13,000 in late 2013, the estimated need for kidney transplant will be of 7410. This estimate should encourage professionals and health authorities of Morocco to engage more effort in the implementation of actions related to the transplant program.
Coupled Ito equations of continuous quantum state measurement, and estimation
Diósi, L; Konrad, T; Scherer, A; Audretsch, Juergen; Diosi, Lajos; Konrad, Thomas; Scherer, Artur
2006-01-01
We discuss a non-linear stochastic master equation that governs the time-evolution of the estimated quantum state. Its differential evolution corresponds to the infinitesimal updates that depend on the time-continuous measurement of the true quantum state. The new stochastic master equation couples to the two standard stochastic differential equations of time-continuous quantum measurement. For the first time, we can prove that the calculated estimate almost always converges to the true state, also at low-efficiency measurements. We show that our single-state theory can be adapted to weak continuous ensemble measurements as well.
Parameter Estimation in Stochastic Differential Equations; An Overview
DEFF Research Database (Denmark)
Nielsen, Jan Nygaard; Madsen, Henrik; Young, P. C.
2000-01-01
This paper presents an overview of the progress of research on parameter estimation methods for stochastic differential equations (mostly in the sense of Ito calculus) over the period 1981-1999. These are considered both without measurement noise and with measurement noise, where the discretely...... observed stochastic differential equations are embedded in a continuous-discrete time state space model. Every attempts has been made to include results from other scientific disciplines. Maximum likelihood estimation of parameters in nonlinear stochastic differential equations is in general not possible...
Analytical Equation for Estimating Terminal Velocities of Spheroidal Particles
Energy Technology Data Exchange (ETDEWEB)
Marshall, Douglas W.
2007-06-01
An analytical method for estimating the terminal velocities of spheroidal particles in a fluid medium has been derived form a graphical approach proposed by Haider and Levenspiel. Using an analytical equation enables the researcher to calculate the terminal velocities without resorting to graphical interpolations, thereby reducing errors and enabling terminal velocities to be estimated in automated calculations.
Equations for estimating selected streamflow statistics in Rhode Island
Bent, Gardner C.; Steeves, Peter A.; Waite, Andrew M.
2014-01-01
Regional regression equations were developed for estimating selected natural—unaffected by alteration—streamflows of specific flow durations and low-flow frequency statistics for ungaged stream sites in Rhode Island. Selected at-site streamflow statistics are provided for 41 long-term streamgages, 21 short-term streamgages, and 135 partial-record stations in Rhode Island, eastern Connecticut, and southeastern and south-central Massachusetts. The regression equations for estimating selected streamflow statistics and the at-site statistics estimated for each of the 197 sites may be used by Federal, State, and local water managers in addressing water issues in and near Rhode Island.
Chudleigh, R A; Ollerton, R L; Dunseath, G; Peter, R; Harvey, J N; Luzio, S; Owens, D R
2008-09-01
Estimation of GFR (eGFR) is recommended for the assessment of kidney function in all patients with diabetes. We studied performance of the traditional '186' Modification of Diet in Renal Disease (MDRD) equation, and the 2005 revised '175' MDRD equation in patients with type 2 diabetes. Two hundred and ninety-three mainly normoalbuminuric (267/293) patients were recruited. Patients were classified as having mild renal impairment (group 1, GFR or=90 ml min(-1) 1.73 m(-2)). eGFR was calculated by the traditional 186 MDRD equation using traditional creatinine values and the revised 175 MDRD equation using isotope dilution mass spectrometry-standardised creatinine values. Isotopic GFR was measured by the four-sample plasma clearance of (51)Cr-EDTA. For patients in group 1, mean +/- SD isotopic (51)Cr-EDTA GFR (iGFR) was 83.8 +/- 4.3 ml min(-1) 1.73 m(-2), and eGFR was 73.2 +/- 11.9 and 75.8 +/- 13.7 ml min(-1) 1.73 m(-2) using the 186 and 175 MDRD equations, respectively. Method bias was -10.6 with the 186 MDRD and -7.9 ml min(-1) 1.73 m(-2) (p < 0.05) with the 175 MDRD equation. In group 2, iGFR was 119.4 +/- 20.2 ml min(-1) 1.73 m(-2), and eGFR was 92.3 +/- 18.6 and 97.5 +/- 21.6 ml min(-1) 1.73 m(-2) using the 186 and 175 MDRD equations, respectively. Method bias was -27.1 with the 186 MDRD equation and -21.9 ml min(-1) 1.73 m(-2) (p < 0.05) with the 175 MDRD equation. In patients newly diagnosed with type 2 diabetes, the revised 175 MDRD equation was less biased than the traditional 186 MDRD equation. Despite a continued tendency to underestimate isotopically measured GFR, use of standardised creatinine values is a positive step towards improved estimation of GFR.
Institute of Scientific and Technical Information of China (English)
LI Jiang-tao; XUN Chen; CUI Chun-li; WANG Hui-fang; WU Yi-tai; YUN Ai-hong; JIANG Xiao-feng; MA Jun
2012-01-01
Background The new Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation was developed to address the systematic underestimation of glomerular filtration rate (GFR) by the Modification of Diet in Renal Disease (MDRD) Study equation in patients with relatively well-preserved kidney function.Performance of the new equation in the Chinese population is unknown.The goal of the present study was to compare performance of these two equations in Chinese patients with chronic kidney disease (CKD).Methods We enrolled 450 Chinese patients (239 women and 211 men) with CKD in the present study.The renal dynamic imaging method was used to measure the referenced standard GFR (rGFR) for comparison with estimations using the two equations.Their overall performance was assessed with the Bland-Altman method and receiver-operating characteristics (ROC) analysis.Performance of the two equations in lower and higher estimated GFR (eGFR) subgroups was further investigated.Results Both eGFRs correlated well with rGFR (r=0.88,0.81,P＜0.05).In overall performance,the CKD-EPI equation showed less bias,higher precision and improved accuracy,and was better for detecting CKD.In the higher-eGFR subgroup,the CKD-EPI equation corrected the underestimation of GFR by the abbreviated MDRD equation.Conclusions The CKD-EPI equation outperformed the abbreviated MDRD equation not only in overall performance but also in the subgroups studied.For the present,the CKD-EPI equation appears to be the first-choice prediction equation for estimating GFR.
Boundary Integral Equations and A Posteriori Error Estimates
Institute of Scientific and Technical Information of China (English)
YU Dehao; ZHAO Longhua
2005-01-01
Adaptive methods have been rapidly developed and applied in many fields of scientific and engineering computing. Reliable and efficient a posteriori error estimates play key roles for both adaptive finite element and boundary element methods. The aim of this paper is to develop a posteriori error estimates for boundary element methods. The standard a posteriori error estimates for boundary element methods are obtained from the classical boundary integral equations. This paper presents hyper-singular a posteriori error estimates based on the hyper-singular integral equations. Three kinds of residuals are used as the estimates for boundary element errors. The theoretical analysis and numerical examples show that the hyper-singular residuals are good a posteriori error indicators in many adaptive boundary element computations.
Statistically and Computationally Efficient Estimating Equations for Large Spatial Datasets
Sun, Ying
2014-11-07
For Gaussian process models, likelihood based methods are often difficult to use with large irregularly spaced spatial datasets, because exact calculations of the likelihood for n observations require O(n3) operations and O(n2) memory. Various approximation methods have been developed to address the computational difficulties. In this paper, we propose new unbiased estimating equations based on score equation approximations that are both computationally and statistically efficient. We replace the inverse covariance matrix that appears in the score equations by a sparse matrix to approximate the quadratic forms, then set the resulting quadratic forms equal to their expected values to obtain unbiased estimating equations. The sparse matrix is constructed by a sparse inverse Cholesky approach to approximate the inverse covariance matrix. The statistical efficiency of the resulting unbiased estimating equations are evaluated both in theory and by numerical studies. Our methods are applied to nearly 90,000 satellite-based measurements of water vapor levels over a region in the Southeast Pacific Ocean.
Maximum Likelihood Estimation in Meta-Analytic Structural Equation Modeling
Oort, Frans J.; Jak, Suzanne
2016-01-01
Meta-analytic structural equation modeling (MASEM) involves fitting models to a common population correlation matrix that is estimated on the basis of correlation coefficients that are reported by a number of independent studies. MASEM typically consist of two stages. The method that has been found to perform best in terms of statistical…
Parameter Estimates in Differential Equation Models for Population Growth
Winkel, Brian J.
2011-01-01
We estimate the parameters present in several differential equation models of population growth, specifically logistic growth models and two-species competition models. We discuss student-evolved strategies and offer "Mathematica" code for a gradient search approach. We use historical (1930s) data from microbial studies of the Russian biologist,…
Maximum Likelihood Estimation of Nonlinear Structural Equation Models.
Lee, Sik-Yum; Zhu, Hong-Tu
2002-01-01
Developed an EM type algorithm for maximum likelihood estimation of a general nonlinear structural equation model in which the E-step is completed by a Metropolis-Hastings algorithm. Illustrated the methodology with results from a simulation study and two real examples using data from previous studies. (SLD)
The Regularity Estimates for the Elliptic Equations in Orlicz Classes
Institute of Scientific and Technical Information of China (English)
TAO Xiang-xing; FANG Yi
2012-01-01
The purpose of this paper is to give the element proof of the regularity estimates in Orlicz classes for the second order derivatives of the solutions to the general second order elliptic equations.The global regularities in Orlicz for the second order derivatives of the solutions of the Dirichlet problems are also given.
Explicit estimating equations for semiparametric generalized linear latent variable models
Ma, Yanyuan
2010-07-05
We study generalized linear latent variable models without requiring a distributional assumption of the latent variables. Using a geometric approach, we derive consistent semiparametric estimators. We demonstrate that these models have a property which is similar to that of a sufficient complete statistic, which enables us to simplify the estimating procedure and explicitly to formulate the semiparametric estimating equations. We further show that the explicit estimators have the usual root n consistency and asymptotic normality. We explain the computational implementation of our method and illustrate the numerical performance of the estimators in finite sample situations via extensive simulation studies. The advantage of our estimators over the existing likelihood approach is also shown via numerical comparison. We employ the method to analyse a real data example from economics. © 2010 Royal Statistical Society.
ALLOMETRIC EQUATIONS FOR ESTIMATING ABOVEGROUND BIOMASS IN PAPUA TROPICAL FOREST
Directory of Open Access Journals (Sweden)
Sandhi Imam Maulana
2014-10-01
Full Text Available Allometric equations can be used to estimate biomass and carbon stock of the forest. However, so far the allometric equations for commercial species in Papua tropical forests have not been appropriately developed. In this research, allometric equations are presented based on the genera of commercial species. Few equations have been developed for the commercial species of Intsia, Pometia, Palaquium and Vatica genera and an equation of a mix of these genera. The number of trees sampled in this research was 49, with diameters (1.30 m above-ground or above buttresses ranging from 5 to 40 cm. Destructive sampling was used to collect the samples where Diameter at Breast Height (DBH and Wood Density (WD were used as predictors for dry weight of Total Above-Ground Biomass (TAGB. Model comparison and selection were based on the values of F-statistics, R-sq, R-sq (adj, and average deviation. Based on these statistical indicators, the most suitable model for Intsia, Pometia, Palaquium and Vatica genera respectively are Log(TAGB = -0.76 + 2.51Log(DBH, Log(TAGB = -0.84 + 2.57Log(DBH, Log(TAGB = -1.52 + 2.96Log(DBH, and Log(TAGB = -0.09 + 2.08Log(DBH. Additional explanatory variables such as Commercial Bole Height (CBH do not really increase the indicators’ goodness of fit for the equation. An alternative model to incorporate wood density should be considered for estimating the above-ground biomass for mixed genera. Comparing the presented mixed-genera equation; Log(TAGB = 0.205 + 2.08Log(DBH + 1.75Log(WD, R-sq: 97.0%, R-sq (adj: 96.9%, F statistics 750.67, average deviation: 3.5%; to previously published datashows that this local species specific equation differs substantially from previously published equations and this site-specific equation is considered to give a better estimation of biomass.
Directory of Open Access Journals (Sweden)
Guillermo J. Rosa-Diez
2011-08-01
Full Text Available La ecuación MDRD para la estimación del índice de filtrado glomerular (IFG, es la estrategia más utilizada para evaluar pacientes con enfermedad renal crónica (ERC. Sin embargo, puede subestimar el IFG con el riesgo de asignar al paciente a estadios más avanzados de ERC. La nueva ecuación CKD-EPI, mejoraría la exactitud y precisión de las estimaciones. Sus autores sugieren que reemplace a la anterior. No habiendo comparaciones de estas ecuaciones aplicadas en un gran número de pacientes en nuestro país, nuestro objetivo fue realizarla en una amplia cohorte de pacientes. Se evaluó la concordancia de asignación en estadios de ERC entre ambas ecuaciones, tomando como referencia los datos surgidos de MDRD. Se calculó la media de las diferencias de los IFG obtenidos empleando ambas ecuaciones y se aplicó el análisis estadístico de Bland-Altman. Se estudió una cohorte de 9 319 pacientes con una media de creatinina sérica de 1.60 ± 1.03 mg/dl, 67% de sexo femenino y edad media 58 ± 20 años. En el grupo total, CKD-EPI presentó una media de IFG 0.61 ml/min/1.73 m² mayor que MDRD (p: NS. En los estadios 2 y 3A las medias del IFG fueron respectivamente 6.95 ± 4.76 y 3.21 ± 3.31, y la concordancia de 81 y 74%. El porcentaje de pacientes con un IFG menor de 60 ml/min/1.73 m², se redujo de 76.3% (MDRD a 70.1% (CKD-EPI. Por lo tanto, la nueva ecuación CKD-EPI disminuye el número de pacientes con IFG debajo de 60 ml/min/1.73 m² y asigna estadios de IFG más elevado a un número mayor de pacientes.The MDRD equation to estimate glomerular filtration rate (GFR is the most widely used strategy to assess chronic kidney disease. Nonetheless, for the individual patient the true GFR can be underestimated with the risk of diagnosing a more elevated CKD stage. This novel CKD-EPI equation would improve accuracy and precision of estimations, and several authors recommend this new equation replace the former. In our country there is only a
A new method for parameter estimation in nonlinear dynamical equations
Wang, Liu; He, Wen-Ping; Liao, Le-Jian; Wan, Shi-Quan; He, Tao
2015-01-01
Parameter estimation is an important scientific problem in various fields such as chaos control, chaos synchronization and other mathematical models. In this paper, a new method for parameter estimation in nonlinear dynamical equations is proposed based on evolutionary modelling (EM). This will be achieved by utilizing the following characteristics of EM which includes self-organizing, adaptive and self-learning features which are inspired by biological natural selection, and mutation and genetic inheritance. The performance of the new method is demonstrated by using various numerical tests on the classic chaos model—Lorenz equation (Lorenz 1963). The results indicate that the new method can be used for fast and effective parameter estimation irrespective of whether partial parameters or all parameters are unknown in the Lorenz equation. Moreover, the new method has a good convergence rate. Noises are inevitable in observational data. The influence of observational noises on the performance of the presented method has been investigated. The results indicate that the strong noises, such as signal noise ratio (SNR) of 10 dB, have a larger influence on parameter estimation than the relatively weak noises. However, it is found that the precision of the parameter estimation remains acceptable for the relatively weak noises, e.g. SNR is 20 or 30 dB. It indicates that the presented method also has some anti-noise performance.
Estimating GFR Among Participants in the Chronic Renal Insufficiency Cohort (CRIC) Study
Anderson, Amanda Hyre; Yang, Wei; Hsu, Chi-yuan; Joffe, Marshall M.; Leonard, Mary B.; Xie, Dawei; Chen, Jing; Greene, Tom; Jaar, Bernard G.; Kao, Patricia; Kusek, John W.; Landis, J. Richard; Lash, James P.; Townsend, Raymond R.; Weir, Matthew R.; Feldman, Harold I.
2012-01-01
Background Glomerular filtration rate (GFR) is considered the best measure of kidney function, but repeated assessment is not feasible in most research studies. Study Design Cross-sectional study of 1,433 participants from the Chronic Renal Insufficiency Cohort (CRIC) Study (i.e., the GFR subcohort) to derive an internal GFR estimating equation using a split sample approach. Setting & Participants Adults from 7 US metropolitan areas with mild to moderate chronic kidney disease; 48% had diabetes and 37% were black. Index Test CRIC GFR estimating equation Reference Test or Outcome Urinary 125I-iothalamate clearance testing (measured GFR) Other Measurements Laboratory measures including serum creatinine and cystatin C, and anthropometrics Results In the validation dataset, the model that included serum creatinine, serum cystatin C, age, gender, and race was the most parsimonious and similarly predictive of mGFR compared to a model additionally including bioelectrical impedance analysis phase angle, CRIC clinical center, and 24-hour urinary creatinine excretion. Specifically, the root mean square errors for the separate model were 0.207 vs. 0.202, respectively. The performance of the CRIC GFR estimating equation was most accurate among the subgroups of younger participants, men, non-blacks, non-Hispanics, those without diabetes, those with body mass index <30 kg/m2, those with higher 24-hour urine creatinine excretion, those with lower levels of high-sensitivity C-reactive protein, and those with higher mGFR. Limitations Urinary clearance of 125I-iothalamate is an imperfect measure of true GFR; cystatin C is not standardized to certified reference material; lack of external validation; small sample sizes limit analyses of subgroup-specific predictors. Conclusions The CRIC GFR estimating equation predicts measured GFR accurately in the CRIC cohort using serum creatinine and cystatin C, age, gender, and race. Its performance was best among younger and healthier
A priori estimates for the complex Hessian equations
Dinew, Slawomir
2011-01-01
We prove some $L^{\\infty}$ a priori estimates as well as existence and stability theorems for the weak solutions of the complex Hessian equations in domains of $C^n$ and on compact K\\"ahler manifolds. We also show optimal $L^p$ integrability for m-subharmonic functions with compact singularities, thus partially confirming a conjecture of Blocki. Finally we obtain a local regularity result for $W^{2,p}$ solutions of the real and complex Hessian equations under suitable regularity assumptions on the right hand side. In the real case the method of this proof improves a result of Urbas.
Directory of Open Access Journals (Sweden)
Liu X
2012-10-01
Full Text Available Xun Liu,1,2,* Mu-hua Cheng,3,* Cheng-gang Shi,1 Cheng Wang,1 Cai-lian Cheng,1 Jin-xia Chen,1 Hua Tang,1 Zhu-jiang Chen,1 Zeng-chun Ye,1 Tan-qi Lou11Division of Nephrology, Department of Internal Medicine, The Third Affiliated Hospital of Sun Yet-sun University, Guangzhou, China; 2College of Biology Engineering, South China University of Technology, Guangzhou, China; 3Department of Nuclear Medicine, The Third Affiliated Hospital of Sun Yet-sun University, Guangzhou, China *These authors contributed equally to this paperBackground: Chronic kidney disease (CKD is recognized worldwide as a public health problem, and its prevalence increases as the population ages. However, the applicability of formulas for estimating the glomerular filtration rate (GFR based on serum creatinine (SC levels in elderly Chinese patients with CKD is limited.Materials and methods: Based on values obtained with the technetium-99m diethylenetriaminepentaacetic acid (99mTc-DTPA renal dynamic imaging method, 319 elderly Chinese patients with CKD were enrolled in this study. Serum creatinine was determined by the enzymatic method. The GFR was estimated using the Cockroft–Gault (CG equation, the Modification of Diet in Renal Disease (MDRD equations, the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI equation, the Jelliffe-1973 equation, and the Hull equation.Results: The median of difference ranged from −0.3–4.3 mL/min/1.73 m2. The interquartile range (IQR of differences ranged from 13.9–17.6 mL/min/1.73 m2. Accuracy with a deviation less than 15% ranged from 27.6%–32.9%. Accuracy with a deviation less than 30% ranged from 53.6%–57.7%. Accuracy with a deviation less than 50% ranged from 74.9%–81.5%. None of the equations had accuracy up to the 70% level with a deviation less than 30% from the standard glomerular filtration rate (sGFR. Bland–Altman analysis demonstrated that the mean difference ranged from −3.0–2.4 mL/min/1.73 m2. However, the
Ji, Misuk; Lee, Yoon-Hee; Kim, Hyesun; Cho, Han-Ik; Yang, Hyun Suk; Navarin, Silvia; Di Somma, Salvatore
2016-01-01
Background Estimated glomerular filtration rate (eGFR) is a widely used index of kidney function. Recently, new formulas such as the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations or the Lund-Malmö equation were introduced for assessing eGFR. We compared them with the Modification of Diet in Renal Disease (MDRD) Study equation in the Korean adult population. Methods The study population comprised 1,482 individuals (median age 51 [42-59] yr, 48.9% males) who received annual physical check-ups during the year 2014. Serum creatinine (Cr) and cystatin C (CysC) were measured. We conducted a retrospective analysis using five GFR estimating equations (MDRD Study, revised Lund-Malmö, and Cr and/or CysC-based CKD-EPI equations). Reduced GFR was defined as eGFR <60 mL/min/1.73 m2. Results For the GFR category distribution, large discrepancies were observed depending on the equation used; category G1 (≥90 mL/min/1.73 m2) ranged from 7.4-81.8%. Compared with the MDRD Study equation, the other four equations overestimated GFR, and CysC-based equations showed a greater difference (-31.3 for CKD-EPICysC and -20.5 for CKD-EPICr-CysC). CysC-based equations decreased the prevalence of reduced GFR by one third (9.4% in the MDRD Study and 2.4% in CKD-EPICysC). Conclusions Our data shows that there are remarkable differences in eGFR assessment in the Korean population depending on the equation used, especially in normal or mildly decreased categories. Further prospective studies are necessary in various clinical settings. PMID:27578504
LOCAL ESTIMATES OF SINGULAR SOLUTION TO GAUSSIAN CURVATURE EQUATION
Institute of Scientific and Technical Information of China (English)
杨云雁
2003-01-01
In this paper, we derive the local estimates of a singular solution near its singular set Z of the Gaussian curvature equation △u(x) + K(x)eu(x) = 0 in Ω \\ Z,in the case that K(x) may be zero on Z, where Ω R2 is a bounded open domain, and Z is a set of finite points.
XLISP-Stat Tools for Building Generalised Estimating Equation Models
Directory of Open Access Journals (Sweden)
Thomas Lumley
1996-12-01
Full Text Available This paper describes a set of Lisp-Stat tools for building Generalised Estimating Equation models to analyse longitudinal or clustered measurements. The user interface is based on the built-in regression and generalised linear model prototypes, with the addition of object-based error functions, correlation structures and model formula tools. Residual and deletion diagnostic plots are available on the cluster and observation level and use the dynamic graphics capabilities of Lisp-Stat.
The cluster bootstrap consistency in generalized estimating equations
Cheng, Guang
2013-03-01
The cluster bootstrap resamples clusters or subjects instead of individual observations in order to preserve the dependence within each cluster or subject. In this paper, we provide a theoretical justification of using the cluster bootstrap for the inferences of the generalized estimating equations (GEE) for clustered/longitudinal data. Under the general exchangeable bootstrap weights, we show that the cluster bootstrap yields a consistent approximation of the distribution of the regression estimate, and a consistent approximation of the confidence sets. We also show that a computationally more efficient one-step version of the cluster bootstrap provides asymptotically equivalent inference. © 2012.
Nonparametric estimation of stochastic differential equations with sparse Gaussian processes
García, Constantino A.; Otero, Abraham; Félix, Paulo; Presedo, Jesús; Márquez, David G.
2017-08-01
The application of stochastic differential equations (SDEs) to the analysis of temporal data has attracted increasing attention, due to their ability to describe complex dynamics with physically interpretable equations. In this paper, we introduce a nonparametric method for estimating the drift and diffusion terms of SDEs from a densely observed discrete time series. The use of Gaussian processes as priors permits working directly in a function-space view and thus the inference takes place directly in this space. To cope with the computational complexity that requires the use of Gaussian processes, a sparse Gaussian process approximation is provided. This approximation permits the efficient computation of predictions for the drift and diffusion terms by using a distribution over a small subset of pseudosamples. The proposed method has been validated using both simulated data and real data from economy and paleoclimatology. The application of the method to real data demonstrates its ability to capture the behavior of complex systems.
Quantitative Compactness Estimates for Hamilton-Jacobi Equations
Ancona, Fabio; Cannarsa, Piermarco; Nguyen, Khai T.
2016-02-01
We study quantitative compactness estimates in {W^{1,1}_{loc}} for the map {S_t}, {t > 0} that is associated with the given initial data {u_0in Lip (R^N)} for the corresponding solution {S_t u_0} of a Hamilton-Jacobi equation u_t+Hbig(nabla_{x} ubig)=0, qquad t≥ 0,quad xinR^N, with a uniformly convex Hamiltonian {H=H(p)}. We provide upper and lower estimates of order {1/\\varepsilon^N} on the Kolmogorov {\\varepsilon}-entropy in {W^{1,1}} of the image through the map S t of sets of bounded, compactly supported initial data. Estimates of this type are inspired by a question posed by Lax (Course on Hyperbolic Systems of Conservation Laws. XXVII Scuola Estiva di Fisica Matematica, Ravello, 2002) within the context of conservation laws, and could provide a measure of the order of "resolution" of a numerical method implemented for this equation.
To estimate an equation explaining the determinants of Dowry
Subhani, Muhammad Imtiaz; Afza, Sarwat
2009-01-01
The focus of this study is to estimate an equation explaining the determinants of dowry. In this paper, we address a very common socio-economic problem for sub-continent, the problem of dowry. From a social planner's perspective, who wants to reduce overall dowry transfers, we consider the effect of change in a few relevant parameters like husband height, wife height, wet land, dry land, years of marriage and years of education for women & men on these decisions. According to the various s...
To Estimate An Equation Explaining The Determinants Of Dowry
Afzal, Sarwat
2009-01-01
The focus of this study is to estimate an equation explaining the determinants of dowry. In this paper, we address a very common socio-economic problem for sub-continent, the problem of dowry. From a social planner's perspective, who wants to reduce overall dowry transfers, we consider the effect of change in a few relevant parameters like husband height, wife height, wet land, dry land, years of marriage and years of education for women & men on these decisions. According to the various ...
Energy Technology Data Exchange (ETDEWEB)
Kato, Fumi, E-mail: fumikato@med.hokudai.ac.jp [Department of Radiology, Hokkaido University Graduate School of Medicine, N15, W7, Kita-ku, Sapporo, Hokkaido 060-8638 (Japan); Kamishima, Tamotsu, E-mail: ktamotamo2@yahoo.co.jp [Department of Radiology, Hokkaido University Graduate School of Medicine, N15, W7, Kita-ku, Sapporo, Hokkaido 060-8638 (Japan); Morita, Ken, E-mail: kenordic@carrot.ocn.ne.jp [Department of Urology, Hokkaido University Graduate School of Medicine, N15, W7, Kita-ku, Sapporo, 060-8638 (Japan); Muto, Natalia S., E-mail: nataliamuto@gmail.com [Department of Radiology, Hokkaido University Graduate School of Medicine, N15, W7, Kita-ku, Sapporo, Hokkaido 060-8638 (Japan); Okamoto, Syozou, E-mail: shozo@med.hokudai.ac.jp [Department of Nuclear Medicine, Hokkaido University Graduate School of Medicine, N15, W7, Kita-ku, Sapporo, 060-8638 (Japan); Omatsu, Tokuhiko, E-mail: omatoku@nirs.go.jp [Department of Radiology, Hokkaido University Graduate School of Medicine, N15, W7, Kita-ku, Sapporo, Hokkaido 060-8638 (Japan); Oyama, Noriko, E-mail: ZAT04404@nifty.ne.jp [Department of Radiology, Hokkaido University Graduate School of Medicine, N15, W7, Kita-ku, Sapporo, Hokkaido 060-8638 (Japan); Terae, Satoshi, E-mail: saterae@med.hokudai.ac.jp [Department of Radiology, Hokkaido University Graduate School of Medicine, N15, W7, Kita-ku, Sapporo, Hokkaido 060-8638 (Japan); Kanegae, Kakuko, E-mail: IZW00143@nifty.ne.jp [Department of Nuclear Medicine, Hokkaido University Graduate School of Medicine, N15, W7, Kita-ku, Sapporo, 060-8638 (Japan); Nonomura, Katsuya, E-mail: k-nonno@med.hokudai.ac.jp [Department of Urology, Hokkaido University Graduate School of Medicine, N15, W7, Kita-ku, Sapporo, 060-8638 (Japan); Shirato, Hiroki, E-mail: shirato@med.hokudai.ac.jp [Department of Radiology, Hokkaido University Graduate School of Medicine, N15, W7, Kita-ku, Sapporo, Hokkaido 060-8638 (Japan)
2011-07-15
Purpose: To evaluate the speed and precision of split renal volume (SRV) measurement, which is the ratio of unilateral renal volume to bilateral renal volume, using a newly developed software for computed tomographic (CT) volumetry and to investigate the usefulness of SRV for the estimation of split renal function (SRF) in kidney donors. Method: Both dynamic CT and renal scintigraphy in 28 adult potential living renal donors were the subjects of this study. We calculated SRV using the newly developed volumetric software built into a PACS viewer (n-SRV), and compared it with SRV calculated using a conventional workstation, ZIOSOFT (z-SRV). The correlation with split renal function (SRF) using {sup 99m}Tc-DMSA scintigraphy was also investigated. Results: The time required for volumetry of bilateral kidneys with the newly developed software (16.7 {+-} 3.9 s) was significantly shorter than that of the workstation (102.6 {+-} 38.9 s, p < 0.0001). The results of n-SRV (49.7 {+-} 4.0%) were highly consistent with those of z-SRV (49.9 {+-} 3.6%), with a mean discrepancy of 0.12 {+-} 0.84%. The SRF also agreed well with the n-SRV, with a mean discrepancy of 0.25 {+-} 1.65%. The dominant side determined by SRF and n-SRV showed agreement in 26 of 28 cases (92.9%). Conclusion: The newly developed software for CT volumetry was more rapid than the conventional workstation volumetry and just as accurate, and was suggested to be useful for the estimation of SRF and thus the dominant side in kidney donors.
Glomerular Filtration Rate Estimation in Renal and Non-Renal Solid Organ Transplantation
DEFF Research Database (Denmark)
Hornum, Mads; Feldt-Rasmussen, Bo
2017-01-01
Following transplantation (TX) of both renal and non-renal organs, a large proportion of patients have renal dysfunction. There are multiple causes for this. Chronic nephrotoxicity and high doses of calcineurin inhibitors are important factors. Preoperative and perioperative factors like...... hypertension, hypotension, drugs and infections may play a causative role as well. Organ-specific causes include hepatorenal syndrome, cirrhosis, low cardiac function, low respiratory function and diabetes developed both before and after TX. It is important to be able to perform precise and valid measurements...
Time-course window estimator for ordinary differential equations linear in the parameters
Vujacic, Ivan; Dattner, Itai; Gonzalez, Javier; Wit, Ernst
2015-01-01
In many applications obtaining ordinary differential equation descriptions of dynamic processes is scientifically important. In both, Bayesian and likelihood approaches for estimating parameters of ordinary differential equations, the speed and the convergence of the estimation procedure may crucial
Time-course window estimator for ordinary differential equations linear in the parameters
Vujacic, Ivan; Dattner, Itai; Gonzalez, Javier; Wit, Ernst
2015-01-01
In many applications obtaining ordinary differential equation descriptions of dynamic processes is scientifically important. In both, Bayesian and likelihood approaches for estimating parameters of ordinary differential equations, the speed and the convergence of the estimation procedure may
Campbell, D A; Chkrebtii, O
2013-12-01
Statistical inference for biochemical models often faces a variety of characteristic challenges. In this paper we examine state and parameter estimation for the JAK-STAT intracellular signalling mechanism, which exemplifies the implementation intricacies common in many biochemical inference problems. We introduce an extension to the Generalized Smoothing approach for estimating delay differential equation models, addressing selection of complexity parameters, choice of the basis system, and appropriate optimization strategies. Motivated by the JAK-STAT system, we further extend the generalized smoothing approach to consider a nonlinear observation process with additional unknown parameters, and highlight how the approach handles unobserved states and unevenly spaced observations. The methodology developed is generally applicable to problems of estimation for differential equation models with delays, unobserved states, nonlinear observation processes, and partially observed histories.
GFR estimating equations: getting closer to the truth?
Rule, Andrew D; Glassock, Richard J
2013-08-01
The application of serum creatinine and cystatin C in patients with CKD has been limited to using estimated glomerular filtration rate (eGFR). Criteria for choosing the best GFR estimating equation are 1) accuracy in estimating measured GFR, 2) optimal discrimination of clinical outcomes, and 3) association with CKD risk factors and outcomes similar to that of measured GFR. Notably, these criteria are often not in agreement; and while the last criterion is the most important, it has been widely overlooked. The primary problem with eGFR is that the non-GFR determinants of serum creatinine and cystatin C, as well as their surrogates (age, sex, and race), associate with CKD risk factors and outcomes. This leads to a distorted understanding of CKD, though eGFR based on serum creatinine appears to be less biased than eGFR based on cystatin C. Because of this problem, the use of eGFR should be limited to settings where knowing actual GFR is relevant and eGFR is more informative about GFR than serum creatinine or cystatin C alone. Such settings include staging CKD severity by GFR and dosing medications cleared by glomerular filtration. Alternatively, the diagnosis of CKD, the longitudinal progression of CKD, and prognostic models for CKD are settings where serum creatinine and cystatin C can be better applied and interpreted without eGFR.
Gaussian estimates for a heat equation on a network
Mugnolo, Delio
2010-01-01
We consider a diffusion problem on a network on whose nodes we impose Dirichlet and generalized, non-local Kirchhoff-type conditions. We prove well-posedness of the associated initial value problem, and we exploit the theory of sub-Markovian and ultracontractive semigroups in order to obtain upper Gaussian estimates for the integral kernel. We conclude that the same diffusion problem is governed by an analytic semigroup acting on all $L^p$-type spaces as well as on suitable spaces of continuous functions. Stability and spectral issues are also discussed. As an application we discuss a system of semilinear equations on a network related to potential transmission problems arising in neurobiology.
Choi, Sae Il
2009-01-01
This study used simulation (a) to compare the kernel equating method to traditional equipercentile equating methods under the equivalent-groups (EG) design and the nonequivalent-groups with anchor test (NEAT) design and (b) to apply the parametric bootstrap method for estimating standard errors of equating. A two-parameter logistic item response…
Estimation of saturation and coherence effects in the KGBJS equation - a non-linear CCFM equation
Deak, Michal
2012-01-01
We solve the modified non-linear extension of the CCFM equation - KGBJS equation - numerically for certain initial conditions and compare the resulting gluon Green functions with those obtained from solving the original CCFM equation and the BFKL and BK equations for the same initial conditions. We improve the low transversal momentum behaviour of the KGBJS equation by a small modification.
INTERVAL STATE ESTIMATION FOR SINGULAR DIFFERENTIAL EQUATION SYSTEMS WITH DELAYS
Directory of Open Access Journals (Sweden)
T. A. Kharkovskaia
2016-07-01
Full Text Available The paper deals with linear differential equation systems with algebraic restrictions (singular systems and a method of interval observer design for this kind of systems. The systems contain constant time delay, measurement noise and disturbances. Interval observer synthesis is based on monotone and cooperative systems technique, linear matrix inequations, Lyapunov function theory and interval arithmetic. The set of conditions that gives the possibility for interval observer synthesis is proposed. Results of synthesized observer operation are shown on the example of dynamical interindustry balance model. The advantages of proposed method are that it is adapted to observer design for uncertain systems, if the intervals of admissible values for uncertain parameters are given. The designed observer is capable to provide asymptotically definite limits on the estimation accuracy, since the interval of admissible values for the object state is defined at every instant. The obtained result provides an opportunity to develop the interval estimation theory for complex systems that contain parametric uncertainty, varying delay and nonlinear elements. Interval observers increasingly find applications in economics, electrical engineering, mechanical systems with constraints and optimal flow control.
Doubly robust and multiple-imputation-based generalized estimating equations.
Birhanu, Teshome; Molenberghs, Geert; Sotto, Cristina; Kenward, Michael G
2011-03-01
Generalized estimating equations (GEE), proposed by Liang and Zeger (1986), provide a popular method to analyze correlated non-Gaussian data. When data are incomplete, the GEE method suffers from its frequentist nature and inferences under this method are valid only under the strong assumption that the missing data are missing completely at random. When response data are missing at random, two modifications of GEE can be considered, based on inverse-probability weighting or on multiple imputation. The weighted GEE (WGEE) method involves weighting observations by the inverse of their probability of being observed. Imputation methods involve filling in missing observations with values predicted by an assumed imputation model, multiple times. The so-called doubly robust (DR) methods involve both a model for the weights and a predictive model for the missing observations given the observed ones. To yield consistent estimates, WGEE needs correct specification of the dropout model while imputation-based methodology needs a correctly specified imputation model. DR methods need correct specification of either the weight or the predictive model, but not necessarily both. Focusing on incomplete binary repeated measures, we study the relative performance of the singly robust and doubly robust versions of GEE in a variety of correctly and incorrectly specified models using simulation studies. Data from a clinical trial in onychomycosis further illustrate the method.
Directory of Open Access Journals (Sweden)
Amrah Javaid
2015-01-01
Full Text Available To compare the measured glomerular filtration rate (rGFR using [99mTc] diethylene triamine pentacetic acid (DTPA clearance or estimated GFR (eGFR by the Modification of Diet in Renal Disease (MDRD equation in cancer patients with raised serum creatinine level, we studied 100 cancer patients; 50 patients with normal serum creatinine (control group and 50 patients with abnormal serum creatinine (study group. History of patients, including site of cancer, chemotherapy regime and dose of chemotherapy, was recorded. The rGFR and eGFR were increased in the study group as compared with the control group, but the GFR recorded by the MDRD formula or DTPA revealed similar values. It is therefore concluded that the MDRD equation may be recommended for eGFR estimation even with abnormal creatinine, without the need for exposure to radiation.
Directory of Open Access Journals (Sweden)
Mahmoud M Elnokeety
2017-01-01
In patients with early overt diabetic nephropathy, serum cystatin C showed a significantly stronger correlation than creatinine with isotopically measured GFR, and among the studied equations for GFR estimation the CKD-EPI Cr-Cyst 2012 equation performed best.
Statistical Assessment of Estimated Transformations in Observed-Score Equating
Wiberg, Marie; González, Jorge
2016-01-01
Equating methods make use of an appropriate transformation function to map the scores of one test form into the scale of another so that scores are comparable and can be used interchangeably. The equating literature shows that the ways of judging the success of an equating (i.e., the score transformation) might differ depending on the adopted…
Lewis, Teresa V; Harrison, Donald L; Gildon, Brooke L; Carter, Sandra M; Turman, Martin A
2016-06-01
To determine if significant correlations exist between glomerular filtration rate (GFR) prediction equation values, derived by using the original Schwartz equation and the Chronic Kidney Disease in Children (CKiD) bedside equation with a 24-hour urine creatinine clearance (Clcr ) value normalized to a body surface area of 1.73 m(2) in overweight and obese children. Prospective analysis (20 patients) and retrospective analysis (43 patients). Pediatric inpatient ward and pediatric nephrology clinic at a comprehensive academic medical center. Sixty-three pediatric patients (aged 5-17 years), of whom 27 were overweight (body mass index [BMI] at the 85th percentile or higher) and 36 were not overweight (BMI lower than the 85th percentile [controls]) between 2007 and 2012. Data from the overweight patients were compared with nonoverweight controls. GFR values were calculated by using the original Schwartz equation and the CKiD bedside equation. Each patient's 24-hour urine Clcr value normalized to a body surface area of 1.73 m(2) served as the index value. A Pearson correlation coefficient model was used to determine association between the 24-hour urine Clcr value (index value) with the Schwartz and CKiD GFR estimations. Significant correlation was found to exist between the Schwartz and CKiD bedside GFR estimations relative to the 24-hour urine Clcr in the control subjects (r = 0.85, pSchwartz and CKiD bedside GFR values with the 24-hour urine Clcr value in overweight subjects (r = 0.86, pSchwartz equation estimated average GFR 21.75 ml/minute/1.73 m(2) higher than 24-hour urine Clcr (pSchwartz and CKiD bedside estimations of GFR correlated with 24-hour urine Clcr values in both overweight and nonoverweight children. Compared with the Schwartz equation, which tended to overestimate renal function, the CKiD bedside equation appeared to approximate 24-hour urine Clcr more closely in overweight children with kidney disorder. © 2016 Pharmacotherapy Publications, Inc.
Trzeciakowski, Jerome P; Gardiner, Lesley; Parrish, Alan R
2014-07-03
A relationship between exposure to heavy metals, including lead and cadmium, and renal dysfunction has long been suggested. However, modeling of the potential additive, or synergistic, impact of metals on renal dysfunction has proven to be challenging. In these studies, we used structural equation modeling (SEM), to investigate the relationship between heavy metal burden (serum and urine levels of lead, cadmium and mercury) and renal function using data from the NHANES database. We were able to generate a model with goodness of fit indices consistent with a well-fitting model. This model demonstrated that lead and cadmium had a negative relationship with renal function, while mercury did not contribute to renal dysfunction. Interestingly, a linear relationship between lead and loss of renal function was observed, while the maximal impact of cadmium occurred at or above serum cadmium levels of 0.8 μg/L. The interaction of lead and cadmium in loss of renal function was also observed in the model. These data highlight the use of SEM to model interaction between environmental contaminants and pathophysiology, which has important implications in mechanistic and regulatory toxicology.
Global attractors of a degenerate parabolic equation and their error estimates
Institute of Scientific and Technical Information of China (English)
HU Xiaohong; ZHANG Xingyou
2004-01-01
The existences of the global attractor A? for a degenerate parabolic equation and of the homogenized attractorA0 for the corresponding homogenized equation are studied, and explicit estimates for the distance between A? and A0 are given.
Energy Technology Data Exchange (ETDEWEB)
Lythgoe, M.F.; Gordon, I.; Khader, Z.; Smith, T.; Anderson, P.J. [Department of Radiology, Great Ormond Street Hospital for Children NHS Trust, London (United Kingdom)
1999-02-01
Differential renal function (DRF) is an important parameter that should be assessed from virtually every dynamic renogram. With the introduction of technetium-99m mercaptoacetyltriglycine ({sup 99m}Tc-MAG3), a tracer with a high renal extraction, the estimation of DRF might hopefully become accurate and reproducible both between observers in the same institution and also between institutions. The aim of this study was to assess the effect of different parameters on the estimation of DRF. To this end we investigated two groups of children: group A, comprising 35 children with a single kidney (27 of whom had poor renal function), and group B, comprising 20 children with two kidneys and normal global function who also had an associated {sup 99m}Tc-dimercaptosuccinic acid scan ({sup 99m}Tc-DMSA). The variables assessed for their effect on the estimation of DRF were: different operators, the choice of renal regions of interest (ROIs), the applied background subtraction, and six different techniques for analysis of the renogram. The six techniques were based on: linear regression of the slopes in the Rutland-Patlak plot, matrix deconvolution, differential method, integral method, linear regression of the slope of the renograms, and the area under the curve of the renogram. The estimation of DRF was less dependent upon both observer and method in patients with two normally functioning kidneys than in patients with a single kidney. The inter-observer comparison among children in either group was not dependent on either ROI or background subtraction. However, in patients with poor renal function the method of choice for the estimation of DRF was dependent on background subtraction, though not ROI. In children with two kidneys and normal renal function, the estimation of DRF from the 24 techniques gave similar results. Methods that produced DRF values closest to expected results, from either group of children, were the Rutland-Patlak plot and matrix deconvolution methods
Directory of Open Access Journals (Sweden)
Ted W. Sammis
2013-09-01
Full Text Available Net radiation is a key component of the energy balance, whose estimation accuracy has an impact on energy flux estimates from satellite data. In typical remote sensing evapotranspiration (ET algorithms, the outgoing shortwave and longwave components of net radiation are obtained from remote sensing data, while the incoming shortwave (RS and longwave (RL components are typically estimated from weather data using empirical equations. This study evaluates the accuracy of empirical equations commonly used in remote sensing ET algorithms for estimating RS and RL radiation. Evaluation is carried out through comparison of estimates and observations at five sites that represent different climatic regions from humid to arid. Results reveal (1 both RS and RL estimates from all evaluated equations well correlate with observations (R2 ≥ 0.92, (2 RS estimating equations tend to overestimate, especially at higher values, (3 RL estimating equations tend to give more biased values in arid and semi-arid regions, (4 a model that parameterizes the diffuse component of radiation using two clearness indices and a simple model that assumes a linear increase of atmospheric transmissivity with elevation give better RS estimates, and (5 mean relative absolute errors in the net radiation (Rn estimates caused by the use of RS and RL estimating equations varies from 10% to 22%. This study suggests that Rn estimates using recommended incoming radiation estimating equations could improve ET estimates.
Parameter estimation in a simple stochastic differential equation for phytoplankton modelling
DEFF Research Database (Denmark)
Møller, Jan Kloppenborg; Madsen, Henrik; Carstensen, Jacob
2011-01-01
The use of stochastic differential equations (SDEs) for simulation of aquatic ecosystems has attracted increasing attention in recent years. The SDE setting also provides the opportunity for statistical estimation of ecosystem parameters. We present an estimation procedure, based on Kalman...... filtering and likelihood estimation, which has proven useful in other fields of application. The estimation procedure is presented and the development from ordinary differential equations (ODEs) to SDEs is discussed with emphasis on autocorrelated residuals, commonly encountered with ODEs. The estimation...
Sourcing for Parameter Estimation and Study of Logistic Differential Equation
Winkel, Brian J.
2012-01-01
This article offers modelling opportunities in which the phenomena of the spread of disease, perception of changing mass, growth of technology, and dissemination of information can be described by one differential equation--the logistic differential equation. It presents two simulation activities for students to generate real data, as well as…
Sourcing for Parameter Estimation and Study of Logistic Differential Equation
Winkel, Brian J.
2012-01-01
This article offers modelling opportunities in which the phenomena of the spread of disease, perception of changing mass, growth of technology, and dissemination of information can be described by one differential equation--the logistic differential equation. It presents two simulation activities for students to generate real data, as well as…
Deriving Biomass Estimation Equations for Seven Plantation Hardwood Species
Bryce E. Schlaegel; Harvey E. Kennedy
1986-01-01
Trees of seven species sampled from a plantation over 7 years were used to derive weight equations to predict primary tree components. The seven species required the use of five different model forms to insure the greatest precision. Regardless of model form, all equations include variables for tree diameter, tree height, age, and number of trees planted. The most...
DECAY ESTIMATES FOR ISENTROPIC COMPRESSIBLE MAGNETOHYDRODYNAMIC EQUATIONS IN BOUNDED DOMAIN
Institute of Scientific and Technical Information of China (English)
Mohamed Ahmed Abdallah; Jiang Fei; Tan Zhong
2012-01-01
In this paper,under the hypothesis that (o) is upper bounded,we construct a Lyapunov functional for the multidimensional isentropic compressible magnetohydrodynamic equations and show that the weak solutions decay exponentially to the equilibrium state in L2 norm.Our result verifies that the method of Daoyuan Fang,Ruizhao Zi and Ting Zhang [1] can be adapted to magnetohydrodynamic equations.
Error Estimates for Approximate Solutions of the Riccati Equation with Real or Complex Potentials
Finster, Felix
2008-01-01
A method is presented for obtaining rigorous error estimates for approximate solutions of the Riccati equation, with real or complex potentials. Our main tool is to derive invariant region estimates for complex solutions of the Riccati equation. We explain the general strategy for applying these estimates and illustrate the method in typical examples, where the approximate solutions are obtained by glueing together WKB and Airy solutions of corresponding one-dimensional Schr"odinger equations.
Classification of tubulo-papillary renal cortical tumours using estimates of nuclear volume
DEFF Research Database (Denmark)
Brooks, B; Sørensen, Flemming Brandt; Olsen, S
1993-01-01
The classification of renal cortical tumours is problematic, with no clear division of benign from malignant tumours. Unbiased stereological estimates of volume-weighted nuclear volume (nuclear vv) were obtained by point sampling of nuclear intercepts in a retrospective study of 36 variably sized...
Directory of Open Access Journals (Sweden)
Eun Young Lee
2013-01-01
Full Text Available Aim. To compare two creatinine-based estimated glomerular filtration rate (eGFR equations, the chronic kidney disease epidemiology collaboration (CKD-EPI and the modification of diet in renal disease (MDRD, for predicting the risk of CKD progression in type 2 diabetic patients with nephropathy. Methods. A total of 707 type 2 diabetic patients with 24 hr urinary albumin excretion of more than 30 mg/day were retrospectively recruited and traced until doubling of baseline serum creatinine (SCr levels was noted. Results. During the follow-up period (median, 2.4 years, the CKD-EPI equation reclassified 10.9% of all MDRD-estimated subjects: 9.1% to an earlier stage of CKD and 1.8% to a later stage of CKD. Overall, the prevalence of CKD (eGFR < 60 mL/min/1.73 m2 was lowered from 54% to 51.6% by applying the CKD-EPI equation. On Cox-regression analysis, both equations exhibited significant associations with an increased risk for doubling of SCr. However, only the CKD-EPI equation maintained a significant hazard ratio for doubling of SCr in earlier-stage CKD (eGFR ≥ 45 mL/min/1.73 m2, when compared to stage 1 CKD (eGFR ≥ 90 mL/min/1.73 m2. Conclusion. In regard to CKD progression, these results suggest that the CKD-EPI equation might more accurately stratify earlier-stage CKD among type 2 diabetic patients with nephropathy than the MDRD study equation.
Solution Estimates for Semilinear Difference-Delay Equations with Continuous Time
Directory of Open Access Journals (Sweden)
Michael Gil'
2007-01-01
Full Text Available We consider semilinear difference-delay equations with continuous time in a Euclidean space. Estimates are found for the solutions. Such estimates are then applied to obtain the stability and boundedness criteria for solutions.
LOCAL A PRIORI AND A POSTERIORI ERROR ESTIMATE OF TQC9 ELEMENT FOR THE BIHARMONIC EQUATION
Institute of Scientific and Technical Information of China (English)
Ming Wang; Weimeng Zhang
2008-01-01
In this paper,local a priori,local a posteriori and global a posteriori error estimates are obtained for TQC9 element for the biharmonic equation.An adaptive algorithm is given based on the a posteriori error estimates.
AN UPPER ESTIMATE OF SOLUTION FOR A GENERALCLASS OF PARABOLIC EQUATIONS
Institute of Scientific and Technical Information of China (English)
Li Shenghong; Wang Xuefeng
2000-01-01
The upper estimates of the functions that satisfy some differentialintegral inequality are established in this paper. We obtain the uniform estimates of maximum of the solutions for a general class of parabolic equations and extend some known results.
A decay estimate for a wave equation with trapping and a complex potential
Andersson, Lars; Nicolas, Jean-Philippe
2011-01-01
In this brief note, we consider a wave equation that has both trapping and a complex potential. For this problem, we prove a uniform bound on the energy and a Morawetz (or integrated local energy decay) estimate. The equation is a model problem for certain scalar equations appearing in the Maxwell and linearised Einstein systems on the exterior of a rotating black hole.
Development and validation of GFR-estimating equations using diabetes, transplant and weight
DEFF Research Database (Denmark)
Stevens, L.A.; Schmid, C.H.; Zhang, Y.L.;
2009-01-01
BACKGROUND: We have reported a new equation (CKD-EPI equation) that reduces bias and improves accuracy for GFR estimation compared to the MDRD study equation while using the same four basic predictor variables: creatinine, age, sex and race. Here, we describe the development and validation of thi...
Estimates and Nonexistence of Solutions of the Scalar Curvature Equation on Noncompact Manifolds
Indian Academy of Sciences (India)
Zhang Zonglao
2005-08-01
This paper is to study the conformal scalar curvature equation on complete noncompact Riemannian manifold of nonpositive curvature. We derive some estimates and properties of supersolutions of the scalar curvature equation, and obtain some nonexistence results for complete solutions of scalar curvature equation.
DEFF Research Database (Denmark)
Petersen, L J; Petersen, J R; Talleruphuus, U
1999-01-01
The purpose of the study was to compare the estimation of glomerular filtration rate (GFR) from 99mTc-DTPA renography with that estimated from the renal clearance of 51Cr-EDTA, creatinine and urea.......The purpose of the study was to compare the estimation of glomerular filtration rate (GFR) from 99mTc-DTPA renography with that estimated from the renal clearance of 51Cr-EDTA, creatinine and urea....
DEFF Research Database (Denmark)
Petersen, L J; Petersen, J R; Talleruphuus, U
1999-01-01
The purpose of the study was to compare the estimation of glomerular filtration rate (GFR) from 99mTc-DTPA renography with that estimated from the renal clearance of 51Cr-EDTA, creatinine and urea.......The purpose of the study was to compare the estimation of glomerular filtration rate (GFR) from 99mTc-DTPA renography with that estimated from the renal clearance of 51Cr-EDTA, creatinine and urea....
Error Estimates for Approximate Solutions of the Riccati Equation with Real or Complex Potentials
Finster, Felix; Smoller, Joel
2010-09-01
A method is presented for obtaining rigorous error estimates for approximate solutions of the Riccati equation, with real or complex potentials. Our main tool is to derive invariant region estimates for complex solutions of the Riccati equation. We explain the general strategy for applying these estimates and illustrate the method in typical examples, where the approximate solutions are obtained by gluing together WKB and Airy solutions of corresponding one-dimensional Schrödinger equations. Our method is motivated by, and has applications to, the analysis of linear wave equations in the geometry of a rotating black hole.
ON THE W1,q ESTIMATE FOR WEAK SOLUTIONS TO A CLASS OF DIVERGENCE ELLIPTIC EQUATIONS
Institute of Scientific and Technical Information of China (English)
周树清; 邓松海; 黎晓勇
2002-01-01
Local W1,q estimates for weak solutions to a class of equations in divergence formDi (aij (x)|Du|p-2Dju) = 0are obtained, where q ＞ p is given. These estimates are very important in obtaining higher regularity for the weak solutions to elliptic equations.
Directory of Open Access Journals (Sweden)
Fang-Rong Yan
2014-01-01
Full Text Available Population pharmacokinetic (PPK models play a pivotal role in quantitative pharmacology study, which are classically analyzed by nonlinear mixed-effects models based on ordinary differential equations. This paper describes the implementation of SDEs in population pharmacokinetic models, where parameters are estimated by a novel approximation of likelihood function. This approximation is constructed by combining the MCMC method used in nonlinear mixed-effects modeling with the extended Kalman filter used in SDE models. The analysis and simulation results show that the performance of the approximation of likelihood function for mixed-effects SDEs model and analysis of population pharmacokinetic data is reliable. The results suggest that the proposed method is feasible for the analysis of population pharmacokinetic data.
Variational estimation of the drift for stochastic differential equations from the empirical density
Batz, Philipp; Ruttor, Andreas; Opper, Manfred
2016-08-01
We present a method for the nonparametric estimation of the drift function of certain types of stochastic differential equations from the empirical density. It is based on a variational formulation of the Fokker-Planck equation. The minimization of an empirical estimate of the variational functional using kernel based regularization can be performed in closed form. We demonstrate the performance of the method on second order, Langevin-type equations and show how the method can be generalized to other noise models.
Variational estimation of the drift for stochastic differential equations from the empirical density
Batz, Philipp; Opper, Manfred
2016-01-01
We present a method for the nonparametric estimation of the drift function of certain types of stochastic differential equations from the empirical density. It is based on a variational formulation of the Fokker-Planck equation. The minimization of an empirical estimate of the variational functional using kernel based regularization can be performed in closed form. We demonstrate the performance of the method on second order, Langevin-type equations and show how the method can be generalized to other noise models.
Institute of Scientific and Technical Information of China (English)
Veli B SHAKHMUROV
2008-01-01
The unique continuation theorems for the anisotropic partial differential-operator equations with variable coefficients in Banach-valued Lp-spaces are studied. To obtain the uniform maximal regularity and the Carleman type estimates for parameter depended differential-operator equations, the sufficient conditions are founded. By using these facts, the unique continuation properties are established. In the application part, the unique continuation properties and Carleman estimates for finite or infinite systems of quasielliptic partial differential equations are studied.
Directory of Open Access Journals (Sweden)
Ye XS
2014-09-01
Full Text Available Xiaoshuang Ye,1 Lu Wei,1 Xiaohua Pei,1 Bei Zhu,1 Jianqing Wu,2 Weihong Zhao1 1Division of Nephrology, Department of Geriatrics, The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu, People’s Republic of China; 2Division of Respiration, Department of Geriatrics, The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu, People’s Republic of China Background: No conventional creatinine- or cystatin C-based glomerular filtration rate (GFR estimation equation performed consistently outstandingly in elderly Chinese in our previous studies. This research aimed to further evaluate the performance of some recently proposed estimation equations based on creatinine and cystatin C, alone or combined, in this specific population. Materials and methods: The equations were validated in a population totaling 419 participants (median age 68 [range 60–94] years. The estimated GFR (eGFR calculated separately by ten equations was compared with the reference GFR (rGFR measured by the 99mTc-DTPA renal dynamic imaging method. Results: Median serum creatinine, cystatin C, and rGFR levels were 0.93 mg/L, 1.13 mg/L, and 74.20 mL/min/1.73 m2, respectively. The Chinese population-developed creatinine- and cystatin C-based (Cscr-cys equation yielded the least median absolute difference (8.81 vs range 9.53–16.32, P<0.05, vs the Chronic Kidney Disease Epidemiology Collaboration serum creatinine equation, the highest proportion of eGFR within 15% and 30% of rGFR (P15 and P30, 55.13 and 85.44, P<0.05 and P<0.01, vs the Chronic Kidney Disease Epidemiology Collaboration serum creatinine equation, and the lowest root mean square error (14.87 vs range 15.30–22.45 in the whole cohort. A substantial agreement of diagnostic consistency between eGFR and rGFR (with a kappa 0.61–0.80 was also observed with the Cscr-cys equation. Moreover, measures of performance in the Cscr-cys equation were consistent across normal to mildly
Shivalli, Siddharudha; Pai, B.H. Santhosh; Acharya, Koteshwara Devadasa; Gopalakrishnan, Ravichandra; Srikanth, Vivek; Reddy, Vishwanath; Haris, Arafat
2016-01-01
Introduction The sonographic findings are of help in evaluating the nephrological diseases. Glomerular filtration rate is another parameter for assessing the reserved renal function and an indicator of prognosis. In clinical practice GFR estimation (eGFR) is done by using a mathematical formula. In our study, we compared the sonographic grading of renal parenchymal changes with eGFR calculated using Modified Diet in Renal Diseases formula based on serum creatinine, age, gender and ethnicity. Aim To evaluate the relevance of sonographic grading of renal parenchymal changes in assessing the severity of the renal disease and comparing it to the eGFR calculated using MDRD formula based on the age, gender and serum creatinine value of the patient. Materials and Methods The adult patients with suspected kidney disease referred for sonography of abdomen were our study participants. As per our study design following strict inclusion and exclusion criteria, patients were selected as study participants and for each of the patient’s renal parenchymal status, serum creatinine, age, gender and ethnicity were documented. Results A total of 70 patients were our study participants, out of which 67.1% were males and 32.9% were females. Our study showed a linear correlation between sonographic grading of renal parenchymal changes with eGFR. Conclusion We conclude that by evaluating the kidneys with sonography and calculating eGFR using MDRD formula the renal status will be more accurately interpreted. PMID:27042555
Institute of Scientific and Technical Information of China (English)
LI Hai-xia; XU Guo-bin; WANG Xue-jing; ZHANG Xu-chu; YANG Jian-mei
2010-01-01
Background The equations for estimating glomerular filtration rate (GFR) based on creatinine have been found to have limitations and have not been generalizable across all populations. Equations based on cystatin C provide an alternative method to estimate GFR. Whether the equation based on cystatin C alone or combined creatinine would improve GFR estimates has not been validated among Chinese patients with chronic kidney disease (CKD) and diabetes. The aim of this study was to compare the performance of the modification of diet in renal disease (MDRD) equation based on creatinine with the five cystatin C-based formulae for estimation of GFR in patients with CKD and diabetes. Methods A total of 166 patients with CKD and 91 patients with type 2 diabetes were enrolled in this study. Cystatin C was measured by using the particle-enhanced immunonephelometric method and estimated formulae proposed by five different investigator teams (Stevens, Ma, Rule, Macisaac and Perkins). The plasma clearance of ~(99m)Tc-DTPA was determined as measured GFR (mGFR).Results For CKD patients, the bias and accuracy for the Ma and Macisaac equations were superior compared with the MDRD, and the mean results for the Ma formula were closer to mGFR than the other equations in CKD stages 2-5. The differences between Macisaac and mGFR in CKD stages 2-4 were significantly less than those in CKD stage 1 or 5.Stevens and Rule's formulae revealed a similar bias and accuracy compared with the MDRD equation. The MDRD formula had a higher accuracy in CKD stages 3-5 as compared with the results in other stages. For diabetic patients, the mean results between Macisaac and mGFR were closer than those of other equations in mGFR≥90 ml.min~(-1).1.73 m~(-2) stage, in GFR 60-89 ml·min~(-1)·1.73 m~(-2) stage, the MDRD formula showed the smallest difference compared with other equations. All equations overestimated GFR in the cases with GFR <60 mi.min~(-1)·1.73 m~(-2) stages. The MDRD formula had a
ENERGY ESTIMATES FOR DELAY DIFFUSION-REACTION EQUATIONS
Institute of Scientific and Technical Information of China (English)
J.A.Ferreira; P.M.da Silva
2008-01-01
In this paper we consider nonlinear delay diffusion-reaction equations with initial and Dirichlet boundary conditions.The behaviour and the stability of the solution of such initial boundary value problems(IBVPs)are studied using the energy method.Simple numerical methods are considered for the computation of numerical approximations to the solution of the nonlinear IBVPs.Using the discrete energy method we study the stability and convergence of the numerical approximations.Numerical experiments are carried out to illustrate our theoretical results.
Radar Rainfall Estimation using a Quadratic Z-R equation
Hall, Will; Rico-Ramirez, Miguel Angel; Kramer, Stefan
2016-04-01
The aim of this work is to test a method that enables the input of event based drop size distributions to alter a quadratic reflectivity (Z) to rainfall (R) equation that is limited by fixed upper and lower points. Results will be compared to the Marshall-Palmer Z-R relation outputs and validated by a network of gauges and a single polarisation weather radar located close to Essen, Germany. The time window over which the drop size distribution measurements will be collected is varied to note any effect on the generated quadratic Z-R relation. The new quadratic algorithm shows some distinct improvement over the Marshall-Palmer relationship through multiple events. The inclusion of a minimum number of Z-R points helped to decrease the associated error by defaulting back to the Marshall-Palmer equation if the limit was not reached. More research will be done to discover why the quadratic performs poorly in some events as there appears to be little correlation between number of drops or mean rainfall amount and the associated error. In some cases it seems the spatial distribution of the disdrometers has a significant effect as a large percentage of the rain bands pass to the north of two of the three disdrometers, frequently in a slightly north-easterly direction. However during widespread precipitation events the new algorithm works very well with reductions compared to the Marshall-Palmer relation.
L~p estimates for -equation on generalized complex ellipsoids
Institute of Scientific and Technical Information of China (English)
王伟
2000-01-01
The estimate of a holomorphic supporting function for the generalized complex ellipsoid in is given, This domain is not decoupled. By using this estimate, the best possible Lp estimates for the equation and some results of function theory on generalized complex ellipsoids are proved.
DEFF Research Database (Denmark)
Orskov, Bjarne; Strandgaard, Svend; Ørskov, Bjarne;
2010-01-01
(CKD-EPI) equation, the Cockcroft-Gault equation adjusted for body surface area and the MDRD equation with cystatin C. Performance was evaluated by mean bias, precision and accuracy. RESULTS: The MDRD equation with cystatin C had 97% of GFR estimates within 30% of measured GFR (accuracy). Both the CKD......-EPI and Cockcroft-Gault equations had an accuracy of 90% whereas the MDRD equation had an accuracy of 83%. This difference of accuracy was especially marked with GFR >60 ml/min/1.73 m(2). CONCLUSION: For estimating GFR in ADPKD patients the MDRD equation with cystatin C incorporated had the best performance...
Tsai, Miao-Yu
2017-04-15
The concordance correlation coefficient (CCC) is a commonly accepted measure of agreement between two observers for continuous responses. This paper proposes a generalized estimating equations (GEE) approach allowing dependency between repeated measurements over time to assess intra-agreement for each observer and inter- and total agreement among multiple observers simultaneously. Furthermore, the indices of intra-, inter-, and total agreement through variance components (VC) from an extended three-way linear mixed model (LMM) are also developed with consideration of the correlation structure of longitudinal repeated measurements. Simulation studies are conducted to compare the performance of the GEE and VC approaches for repeated measurements from longitudinal data. An application of optometric conformity study is used for illustration. In conclusion, the GEE approach allowing flexibility in model assumptions and correlation structures of repeated measurements gives satisfactory results with small mean square errors and nominal 95% coverage rates for large data sets, and when the assumption of the relationship between variances and covariances for the extended three-way LMM holds, the VC approach performs outstandingly well for all sample sizes. Copyright © 2017 John Wiley & Sons, Ltd. Copyright © 2017 John Wiley & Sons, Ltd.
Aleksandrov-Bakelman-Pucci Type Estimates For Integro-Differential Equations
Guillen, Nestor
2011-01-01
In this work we provide an Aleksandrov-Bakelman-Pucci type estimate for a certain class of fully nonlinear elliptic integro-differential equations and generalizations of both the Monge-Amp\\`ere operator and the convex envelope to a nonlocal, fractional-order setting. This particular elliptic family under consideration is large enough to capture the second order theory as the order of the integro-differential equations tends to 2. Moreover, our estimate is uniform in the order of the equations, resulting in a genuine generalization of the existing ABP estimate. This result also gives a new comparison theorem for viscosity solutions of such equations which only depends on the $L^\\infty$ and $L^n$ norms of the right hand side, in contrast to previous comparison results which utilize the continuity of the right hand side for their conclusions. These results appear to be new even for the linear case of the relevant equations.
Two novel equations to estimate kidney function in persons aged 70 years or older.
Schaeffner, Elke S; Ebert, Natalie; Delanaye, Pierre; Frei, Ulrich; Gaedeke, Jens; Jakob, Olga; Kuhlmann, Martin K; Schuchardt, Mirjam; Tölle, Markus; Ziebig, Reinhard; van der Giet, Markus; Martus, Peter
2012-10-02
In older adults, current equations to estimate glomerular filtration rate (GFR) are not validated and may misclassify elderly persons in terms of their stage of chronic kidney disease. To derive the Berlin Initiative Study (BIS) equation, a novel estimator of GFR in elderly participants. Cross-sectional. Data were split for analysis into 2 sets for equation development and internal validation. Random community-based population of a large insurance company. 610 participants aged 70 years or older (mean age, 78.5 years). Iohexol plasma clearance measurement as gold standard. GFR, measured as the plasma clearance of the endogenous marker iohexol, to compare performance of existing equations of estimated GFR with measured GFR of the gold standard; estimation of measured GFR from standardized creatinine and cystatin C levels, sex, and age in the learning sample; and comparison of the BIS equations (BIS1: creatinine-based; BIS2: creatinine- and cystatin C-based) with other estimating equations and determination of bias, precision, and accuracy in the validation sample. The new BIS2 equation yielded the smallest bias followed by the creatinine-based BIS1 and Cockcroft-Gault equations. All other equations considerably overestimated GFR. The BIS equations confirmed a high prevalence of persons older than 70 years with a GFR less than 60 mL/min per 1.73 m2 (BIS1, 50.4%; BIS2, 47.4%; measured GFR, 47.9%). The total misclassification rate for this criterion was smallest for the BIS2 equation (11.6%), followed by the cystatin C equation 2 (15.1%) proposed by the Chronic Kidney Disease Epidemiology Collaboration. Among the creatinine-based equations, BIS1 had the smallest misclassification rate (17.2%), followed by the Chronic Kidney Disease Epidemiology Collaboration equation (20.4%). There was no validation by an external data set. The BIS2 equation should be used to estimate GFR in persons aged 70 years or older with normal or mild to moderately reduced kidney function. If
Schauder estimates for parabolic equation of bi-harmonic type
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
Global Schauder estimates for the initial-value parabolic problem of the bi-harmonic type are proved, and the existence and uniqueness of the solutions in the suitable space are obtained. Similarly to the second-order case, first a formal expression of solutions by the Fourier transform is obtained, and then the regularity, uniqueness and existence of solutions using the potential theory and approximation argument are got.out approach is simple and straightforward.
Regression Equations for Stature Estimation among Medical Students of Ghaziabad
Rakhee Verma, Syed Esam Mahmood
2015-01-01
"Introduction: Ossification and maturation in the foot occurs earlier than the long bones and therefore, during adolescence height could be more accurately predicted from foot measurement as compared to that from long bones. This study was undertaken to find out the correlation between foot length and height of an individual and to derive regression formulae to estimate the height from the foot length in the study population. Materials & Method: This cross sectional study was cond...
A gradient estimate for solutions to parabolic equations with discontinuous coefficients
Directory of Open Access Journals (Sweden)
Jishan Fan
2013-04-01
Full Text Available Li-Vogelius and Li-Nirenberg gave a gradient estimate for solutions of strongly elliptic equations and systems of divergence forms with piecewise smooth coefficients, respectively. The discontinuities of the coefficients are assumed to be given by manifolds of codimension 1, which we called them emph{manifolds of discontinuities}. Their gradient estimate is independent of the distances between manifolds of discontinuities. In this paper, we gave a parabolic version of their results. That is, we gave a gradient estimate for parabolic equations of divergence forms with piecewise smooth coefficients. The coefficients are assumed to be independent of time and their discontinuities are likewise the previous elliptic equations. As an application of this estimate, we also gave a pointwise gradient estimate for the fundamental solution of a parabolic operator with piecewise smooth coefficients. Both gradient estimates are independent of the distances between manifolds of discontinuities.
A Priori Estimates for Solutions of Boundary Value Problems for Fractional-Order Equations
Alikhanov, A A
2011-01-01
We consider boundary value problems of the first and third kind for the diffusionwave equation. By using the method of energy inequalities, we find a priori estimates for the solutions of these boundary value problems.
Blow-up estimates for semilinear parabolic systems coupled in an equation and a boundary condition
Institute of Scientific and Technical Information of China (English)
王明新
2001-01-01
This paper deals with the blow-up rate estimates of solutions for semilinear parabolic systems coupled in an equation and a boundary condition. The upper and lower bounds of blow-up rates have been obtained.
Energy Technology Data Exchange (ETDEWEB)
Silver, Gary L [Los Alamos National Laboratory
2009-01-01
Equations for interpolating five data in rectangular array are seldom encountered in textbooks. This paper describes a new method that renders polynomial and exponential equations for the design. Operational center point estimators are often more more resistant to the effects of an outlying datum than the mean.
Error estimates for asymptotic solutions of dynamic equations on time scales
Directory of Open Access Journals (Sweden)
Gro Hovhannisyan
2007-02-01
Full Text Available We establish error estimates for first-order linear systems of equations and linear second-order dynamic equations on time scales by using calculus on a time scales [1,4,5] and Birkhoff-Levinson's method of asymptotic solutions [3,6,8,9].
Gurka, Matthew J; Kuperminc, Michelle N; Busby, Marjorie G; Bennis, Jacey A; Grossberg, Richard I; Houlihan, Christine M; Stevenson, Richard D; Henderson, Richard C
2010-02-01
To assess the accuracy of skinfold equations in estimating percentage body fat in children with cerebral palsy (CP), compared with assessment of body fat from dual energy X-ray absorptiometry (DXA). Data were collected from 71 participants (30 females, 41 males) with CP (Gross Motor Function Classification System [GMFCS] levels I-V) between the ages of 8 and 18 years. Estimated percentage body fat was computed using established (Slaughter) equations based on the triceps and subscapular skinfolds. A linear model was fitted to assess the use of a simple correction to these equations for children with CP. Slaughter's equations consistently underestimated percentage body fat (mean difference compared with DXA percentage body fat -9.6/100 [SD 6.2]; 95% confidence interval [CI] -11.0 to -8.1). New equations were developed in which a correction factor was added to the existing equations based on sex, race, GMFCS level, size, and pubertal status. These corrected equations for children with CP agree better with DXA (mean difference 0.2/100 [SD=4.8]; 95% CI -1.0 to 1.3) than existing equations. A simple correction factor to commonly used equations substantially improves the ability to estimate percentage body fat from two skinfold measures in children with CP.
Huygens, W; Claessens, A L; Thomis, M; Loos, R; Van Langendonck, L; Peeters, M; Philippaerts, R; Meynaerts, E; Vlietinck, R; Beunen, G
2002-03-01
Two main questions are stated: 1) are BIA and anthropometric equations accurate in estimating body composition in male power athletes and more specifically in body builders and 2) is there a difference in body composition when body builders are compared to weight and power lifters? this is a descriptive, comparative study on a selected sample of power athletes. 49 Belgian elite and sub-top male power athletes (34 body builders and 15 weight and power lifters) were included in this sample. More than 70% was in preparation of competition at time of data collection. an extended set of anthropometric measures was taken. Body composition was estimated by BIA (Bioelectrical Impedance Analysis) and by regression equations of skinfolds. Somatotype and muscle+bone areas were calculated. Factor analysis on all anthropometric measures was carried out to determine the body structure of the athletes. Compared to external visual criteria, the equations of Durnin and Womersley and Lohman (skinfolds) and the Guo-equation (BIA) were the only equations that could accurately estimate the body composition for this specific group of athletes. However, the sum of skinfolds attains the most accurate estimate of subcutaneous fatness. Body builders have significantly (pathletes (5.9 vs 3.8). This study shows that to estimate body composition in extreme power athletes BIA is not as accurate as compared to anthropometric equations. Moreover, the sum of a larger set of skinfolds is preferred to anthropometric prediction equations. In addition, body builders are more muscular and leaner than other power athletes.
ERROR ESTIMATES FOR THE TIME DISCRETIZATION FOR NONLINEAR MAXWELL'S EQUATIONS
Institute of Scientific and Technical Information of China (English)
Marián Slodi(c)ka; Ján Bu(s)a Jr.
2008-01-01
This paper is devoted to the study of a nonlinear evolution eddy current model of the type (б)tB(H) +▽×(▽×H) = 0 subject to homogeneous Dirichlet boundary conditions H×v = 0 and a given initial datum. Here, the magnetic properties of a soft ferromagnet are linked by a nonlinear material law described by B(H). We apply the backward Euler method for the time discretization and we derive the error estimates in suitable function spaces. The results depend on the nonlinearity of B(H).
Database of 478 allometric equations to estimate biomass for Mexican trees and forests
Rojas-García, Fabiola; Bernardus H. J. De Jong; Martínez-Zurimendí, Pablo; Paz-Pellat, Fernando
2015-01-01
International audience; Key messageWe present a comprehensive database of 478 allometric equations to estimate biomass of trees and other life forms in Mexican forest and scrubland ecosystems.ContextAccurate estimation of standing biomass in forests is a prerequisite for any approach to carbon storage and a number of additional applications.AimsTo provide a comprehensive database with allometric equations applicable to a large number of tree and shrub species of Mexico.MethodsAn intensive lit...
Applicability of various estimation formulas to assess renal function in Chinese children
Institute of Scientific and Technical Information of China (English)
Yue Du; Ting-Ting Sun; Ling Hou; Jin-Jie Guo; Xiu-Li Wang; Yu-Bin Wu
2015-01-01
Background: This study was to evaluate the relative applicability of the most commonly used estimation formulas for renal glomerular filtration rate (GFR) of Chinese children with chronic kidney disease (CKD). Methods: One hundred CKD patients of less than 17 years old were divided into two groups by sex which was further categorized intofi ve subgroups based on CKD staging according to the "reference" GFR (rGFR) determined by Tc-99m-DTPA renal dynamic imaging. Four GFR markers including serum cystatin C (CysC),β2-microglobulin, creatinine, and blood urea nitrogen were measured. Results: Among all four markers, CysC best refl ected the extent of glomerular damages for CKD stage 1. The value for estimation of GFR (eGFR) was derived from five different formulas either over-estimated or under-estimated GFR as referenced to rGFR, and the extent of deviations was dependent on gender, age and CKD stage. The Counahan-Barratt formula and the Schwartz formula gave the most accurate estimations of GFR for CKD stages 1 and 2-3, respectively regardless of gender and age differences. Receiver operating characteristic analyses indicated that the Counahan-Barratt formula has the highest diagnostic accuracy. Conclusion: The Counahan-Barratt formula provides the best approximation to rGFR, thereby the highest applicability to Chinese children with CKD of different genders, ages and CKD stages.
Ahearn, Elizabeth A.
2010-01-01
Multiple linear regression equations for determining flow-duration statistics were developed to estimate select flow exceedances ranging from 25- to 99-percent for six 'bioperiods'-Salmonid Spawning (November), Overwinter (December-February), Habitat Forming (March-April), Clupeid Spawning (May), Resident Spawning (June), and Rearing and Growth (July-October)-in Connecticut. Regression equations also were developed to estimate the 25- and 99-percent flow exceedances without reference to a bioperiod. In total, 32 equations were developed. The predictive equations were based on regression analyses relating flow statistics from streamgages to GIS-determined basin and climatic characteristics for the drainage areas of those streamgages. Thirty-nine streamgages (and an additional 6 short-term streamgages and 28 partial-record sites for the non-bioperiod 99-percent exceedance) in Connecticut and adjacent areas of neighboring States were used in the regression analysis. Weighted least squares regression analysis was used to determine the predictive equations; weights were assigned based on record length. The basin characteristics-drainage area, percentage of area with coarse-grained stratified deposits, percentage of area with wetlands, mean monthly precipitation (November), mean seasonal precipitation (December, January, and February), and mean basin elevation-are used as explanatory variables in the equations. Standard errors of estimate of the 32 equations ranged from 10.7 to 156 percent with medians of 19.2 and 55.4 percent to predict the 25- and 99-percent exceedances, respectively. Regression equations to estimate high and median flows (25- to 75-percent exceedances) are better predictors (smaller variability of the residual values around the regression line) than the equations to estimate low flows (less than 75-percent exceedance). The Habitat Forming (March-April) bioperiod had the smallest standard errors of estimate, ranging from 10.7 to 20.9 percent. In
Solving Richards Equation for snow improves snowpack meltwater runoff estimations
Directory of Open Access Journals (Sweden)
N. Wever
2013-06-01
Full Text Available The runoff from the snow cover during spring snow melt or rain-on-snow events is an important factor in the hydrological cycle. In this study, water transport schemes for a 1-dimensional physical based snowpack model are compared to 14 yr of lysimeter measurements at a high alpine site. The schemes include a simple bucket-type approach, an approximation of Richards Equation (RE, and the full RE. The results show that daily sums of runoff are strongly related to a positive energy balance of the snow cover and therefore, all water transport schemes show very similar performance in terms of Nash–Sutcliffe efficiency (NSE coefficients (around 0.59 and r2 values (around 0.77. Timing of the arrival of meltwater in spring at the bottom of the snowpack showed differences between the schemes, where especially in the bucket-type and approximated RE approach, meltwater release is slower than in the measurements. Overall, solving RE for the snow cover yields the best agreement between modelled and measured runoff. On sub-daily time scales, the water transport schemes behave very differently. Also here, solving RE provides the highest agreement between modelled and measured runoff in terms of NSE coefficient (0.48, where other water transport schemes loose any predictive power. This appears to be mainly due to bad timing of meltwater release during the day. Accordingly, solving RE for the snow cover improves several aspects of modelling snow cover runoff. The additional computational cost was found to be in the order of a factor of 1.5.
Directory of Open Access Journals (Sweden)
Andreia Amaro
2015-05-01
Full Text Available Introduction – The estimate of relative renal function (RRF through scintigraphy with dimercaptosuccinic acid labelled with Technetium-99 metastable (99mTc-DMSA may be influenced by kidney depth (KD, due to attenuation by soft tissue surrounding the kidneys. Considering that rarely this KD is known, several methods for attenuation correction (AC have been developed, namely those using empirical formulae, such as Raynaud, Taylor or Tonnesen methods, or by direct calculation of the geometric mean (GM. Objectives – To identify the influence of different AC methods on RRF estimateby scintigraphy with 99mTc-DMSA and to evaluate the respective KD variability. Methods: Thirty-one patients were referred for 99mTc-DMSA scintigraphy and underwent the same acquisition protocol. Processing was performed by 2 independent operators, three times per exam, changing for the same processing the methods for the FRR determination: Raynaud’s method, Taylor’s method, Tonnesen´s method, GM and without AC (WAC. Friedman’s test was used to identify the influence of the different AC methods on RRF estimate and Pearson’s correlation test was used to evaluate the association and significance between KD and the variables age, weight and height. Results – Friedman’s test indicated that there were significant differences between methods (p=0.000, except for WAC/Raynaud, Tonnesen/GM and Taylor/GM (p=1.000 comparisons, for both kidneys. Pearson’stest showed a strong positive correlation between weight and the three methods of KD estimation. Conclusions – Taylor’s method, regarding the three methods of KD calculation, is the closest to GM. The choice of the attenuation correction method influences significantly the quantitative parameters of FRR.
Allometric Equations for Estimating Carbon Stocks in Natural Forest in New Zealand
Directory of Open Access Journals (Sweden)
Andrea Brandon
2012-09-01
Full Text Available Species-specific and mixed-species volume and above ground biomass allometric equations were developed for 15 indigenous tree species and four tree fern species in New Zealand. A mixed-species tree equation based on breast height diameter (DBH and tree height (H provided acceptable estimates of stem plus branch (>10 cm in diameter over bark volume, which was multiplied by live tree density to estimate dry matter. For dead standing spars, DBH, estimated original height, actual spar height and compatible volume/taper functions provided estimates of dead stem volume, which was multiplied by live tree density and a density modifier based on log decay class from field assessments to estimate dry matter. Live tree density was estimated using ratio estimators. Ratio estimators were based on biomass sample trees, and utilized density data from outerwood basic density surveys which were available for 35 tree species sampled throughout New Zealand. Foliage and branch ( < 10 cm in diameter over bark dry matter were estimated directly from tree DBH. Tree fern above ground dry matter was estimated using allometric equations based on DBH and H. Due to insufficient data, below ground carbon for trees was estimated using the default IPCC root/shoot ratio of 25%, but for tree ferns it was estimated using measured root/shoot ratios which averaged 20%.
Institute of Scientific and Technical Information of China (English)
Veli; B; SHAKHMUROV
2008-01-01
The unique continuation theorems for the anisotropic partial differential-operator equations with variable coeffcients in Banach-valued Lp-spaces are studied.To obtain the uniform maximal regularity and the Carleman type estimates for parameter depended differential-operator equations,the suffcient conditions are founded.By using these facts,the unique continuation properties are established.In the application part,the unique continuation properties and Carleman estimates for finite or infinite systems of quasielliptic partial differential equations are studied.
Kato Smoothing and Strichartz Estimates for Wave Equations with Magnetic Potentials
D'Ancona, Piero
2015-04-01
Let H be a selfadjoint operator and A a closed operator on a Hilbert space . If A is H-(super)smooth in the sense of Kato-Yajima, we prove that is -(super)smooth. This allows us to include wave and Klein-Gordon equations in the abstract theory at the same level of generality as Schrödinger equations. We give a few applications and in particular, based on the resolvent estimates of Erdogan, Goldberg and Schlag (Forum Mathematicum 21:687-722, 2009), we prove Strichartz estimates for wave equations perturbed with large magnetic potentials on , n ≥ 3.
Directory of Open Access Journals (Sweden)
Espen R. Jakobsen
2002-05-01
Full Text Available Using the maximum principle for semicontinuous functions [3,4], we prove a general ``continuous dependence on the nonlinearities'' estimate for bounded Holder continuous viscosity solutions of fully nonlinear degenerate elliptic equations. Furthermore, we provide existence, uniqueness, and Holder continuity results for bounded viscosity solutions of such equations. Our results are general enough to encompass Hamilton-Jacobi-Bellman-Isaacs's equations of zero-sum, two-player stochastic differential games. An immediate consequence of the results obtained herein is a rate of convergence for the vanishing viscosity method for fully nonlinear degenerate elliptic equations.
Krylov, N. V.; Priola, E.
2017-09-01
We show, among other things, how knowing Schauder or Sobolev-space estimates for the one-dimensional heat equation allows one to derive their multidimensional analogs for equations with coefficients depending only on the time variable with the same constants as in the case of the one-dimensional heat equation. The method is quite general and is based on using the Poisson stochastic process. It also applies to equations involving non-local operators. It looks like no other methods are available at this time and it is a very challenging problem to find a purely analytical approach to proving such results.
David C. Chojnacky; Jennifer C. Jenkins; Amanda K. Holland
2009-01-01
Thousands of published equations purport to estimate biomass of individual trees. These equations are often based on very small samples, however, and can provide widely different estimates for trees of the same species. We addressed this issue in a previous study by devising 10 new equations that estimated total aboveground biomass for all species in North America (...
Panel Data Estimation of Labour Supply Equations for Dutch Dairy Farmers
Ooms, D.L.; Hall, A.
2005-01-01
This research focuses on the estimation of labour supply equations for Dutch dairy farmers. Off-farm labour supply is characterised by the fact that only half of the farm households supply off-farm labour. This results in a sample selection estimation problem that has to be taken into account in est
Generalized equations for estimating DXA percent fat of diverse young women and men: The Tiger Study
Popular generalized equations for estimating percent body fat (BF%) developed with cross-sectional data are biased when applied to racially/ethnically diverse populations. We developed accurate anthropometric models to estimate dual-energy x-ray absorptiometry BF% (DXA-BF%) that can be generalized t...
Decay estimates for fractional wave equations on H-type groups
Directory of Open Access Journals (Sweden)
Manli Song
2016-10-01
Full Text Available Abstract The aim of this paper is to establish the decay estimate for the fractional wave equation semigroup on H-type groups given by e i t Δ α $e^{it\\Delta^{\\alpha}}$ , 0 < α < 1 $0<\\alpha<1$ . Combining the dispersive estimate and a standard duality argument, we also derive the corresponding Strichartz inequalities.
CSIR Research Space (South Africa)
Kirton, A
2010-08-01
Full Text Available with estimated values. In the case of allometric equations, information about the original fitting of the allometric relationship is needed in order to put a prediction interval around an estimated value. However, often all the information required to calculate...
Fan, Xitao; Wang, Lin; Thompson, Bruce
1999-01-01
A Monte Carlo simulation study investigated the effects on 10 structural equation modeling fit indexes of sample size, estimation method, and model specification. Some fit indexes did not appear to be comparable, and it was apparent that estimation method strongly influenced almost all fit indexes examined, especially for misspecified models. (SLD)
An estimator for the relative entropy rate of path measures for stochastic differential equations
Opper, Manfred
2017-02-01
We address the problem of estimating the relative entropy rate (RER) for two stochastic processes described by stochastic differential equations. For the case where the drift of one process is known analytically, but one has only observations from the second process, we use a variational bound on the RER to construct an estimator.
Lemarchand, Guillermo A.
2004-06-01
Based on the study of several long-term societal indicators we estimate the phase transition between the ``Technological Adolescent Age'' (TAA) and the ``Technological Mature Age'' (TMA). Assuming the ``Principle of Mediocrity'' and using the Drake Equation we estimate a lower threshold for the number of technological civilizations in the galaxy.
Error estimates for finite element solution for parabolic integro-differential equations
Directory of Open Access Journals (Sweden)
Hasan N. Ymeri
1993-05-01
Full Text Available In this paper we first study the stability of Ritz-Volterra projection and its maximum norm estimates, and then we use these results to derive some L\\infty error estimates for finite element methods for parabolic partial integro-differential equations.
A maximum likelihood estimation framework for delay logistic differential equation model
Mahmoud, Ahmed Adly; Dass, Sarat Chandra; Muthuvalu, Mohana S.
2016-11-01
This paper will introduce the maximum likelihood method of estimation for delay differential equation model governed by unknown delay and other parameters of interest followed by a numerical solver approach. As an example we consider the delayed logistic differential equation. A grid based estimation framework is proposed. Our methodology estimates correctly the delay parameter as well as the initial starting value of the dynamical system based on simulation data. The computations have been carried out with help of mathematical software: MATLAB® 8.0 R2012b.
Canepa, Edward S.
2017-06-19
Nowadays, traffic management has become a challenge for urban areas, which are covering larger geographic spaces and facing the generation of different kinds of traffic data. This article presents a robust traffic estimation framework for highways modeled by a system of Lighthill Whitham Richards equations that is able to assimilate different sensor data available. We first present an equivalent formulation of the problem using a Hamilton–Jacobi equation. Then, using a semi-analytic formula, we show that the model constraints resulting from the Hamilton–Jacobi equation are linear ones. We then pose the problem of estimating the traffic density given incomplete and inaccurate traffic data as a Mixed Integer Program. We then extend the density estimation framework to highway networks with any available data constraint and modeling junctions. Finally, we present a travel estimation application for a small network using real traffic measurements obtained obtained during Mobile Century traffic experiment, and comparing the results with ground truth data.
Solutions to estimation problems for scalar hamilton-jacobi equations using linear programming
Claudel, Christian G.
2014-01-01
This brief presents new convex formulations for solving estimation problems in systems modeled by scalar Hamilton-Jacobi (HJ) equations. Using a semi-analytic formula, we show that the constraints resulting from a HJ equation are convex, and can be written as a set of linear inequalities. We use this fact to pose various (and seemingly unrelated) estimation problems related to traffic flow-engineering as a set of linear programs. In particular, we solve data assimilation and data reconciliation problems for estimating the state of a system when the model and measurement constraints are incompatible. We also solve traffic estimation problems, such as travel time estimation or density estimation. For all these problems, a numerical implementation is performed using experimental data from the Mobile Century experiment. In the context of reproducible research, the code and data used to compute the results presented in this brief have been posted online and are accessible to regenerate the results. © 2013 IEEE.
Directory of Open Access Journals (Sweden)
Sandhi Imam Maulana
2016-10-01
Full Text Available Recently, pantropical allometric equations have been commonly used across the globe to estimate the aboveground biomass of the forests, including in Indonesia. However, in relation to regional differences in diameter, height and wood density, the lack of data measured, particularly from eastern part of Indonesia, may raise the question on accuracy of pantropical allometric in such area. Hence, this paper examines the differences of local allometric equations of Papua Island with equations developed by Chave and his research groups.. Measurements of biomass in this study were conducted directly based on weighing and destructive samplings. Results show that the most appropriate local equation to estimate total aboveground biomass in Papua tropical forest is Log(TAGB = -0.267 + 2.23 Log(DBH +0.649 Log(WD (CF=1.013; VIF=1.6; R2= 95%; R2-adj= 95.1%; RMSE= 0.149; P<0.001. This equation is also a better option in comparison to those of previously published pantropical equations with only 6.47% average deviation and 5.37 points of relative bias. This finding implies that the locally developed equation should be a better option to produce more accurate site specific total aboveground biomass estimation.
Dynamic renal scintigraphic estimation of deceased donor kidneys in a rat model
Directory of Open Access Journals (Sweden)
Huseyin Aydin Mitil
2017-01-01
Full Text Available At present a large number of the renal transplantations are being performed from the deceased donors. The success of these transplantations depends on the viability of the deceased donor kidneys. The aim of this study was to investigate the reliability of scintigraphic estimation of function of deceased donor kidneys by comparing the histopathologic and scintigraphic findings. Ten rats were included in the study (2–3 months old, 250–300 g, all male. Control scintigraphy was performed to all the rats by injection of 37 MBq Tc-99m DTPA from the tail vein in a dynamic manner. Brain death of the rats was achieved by inflation of a Fogartys catheter in the cranial cavity. Immediately, after brain death confirmation, dynamic renal scintigraphy was performed with the same parameters of control scintigraphy. In the comparison of scintigraphies obtained in the before and just after brain death period, there was impairment of tubular functions, concentration and excretion functions in the postbrain death period. In the immediate postbrain death period, there was a significant elevation in the glomerular filtration rate and time to maximum concentration values. In the histopathological evaluation of the kidney samples in the postbrain death period, there were definitive findings of tubular impairment. Dynamic renal scintigraphy also demonstrated definite impairment of tubular system and tubular functions in the deceased donor kidneys. This could explain the reason of the increased frequency of acute tubular necrosis seen among deceased donor kidneys.
Energy Technology Data Exchange (ETDEWEB)
Ju, Lili; Tian, Li; Wang, Desheng
2008-10-31
In this paper, we present a residual-based a posteriori error estimate for the finite volume discretization of steady convection– diffusion–reaction equations defined on surfaces in R3, which are often implicitly represented as level sets of smooth functions. Reliability and efficiency of the proposed a posteriori error estimator are rigorously proved. Numerical experiments are also conducted to verify the theoretical results and demonstrate the robustness of the error estimator.
Institute of Scientific and Technical Information of China (English)
Ningning YAN; Zhaojie ZHOU
2008-01-01
In this paper,we study a posteriori error estimates of the edge stabilization Galerkin method for the constrained optimal control problem governed by convection-dominated diffusion equations.The residual-type a posteriori error estimators yield both upper and lower bounds for control u measured in L2-norm and for state y and costate p measured in energy norm.Two numerical examples are presented to illustrate the effectiveness of the error estimators provided in this paper.
Sex-Specific Equations to Estimate Maximum Oxygen Uptake in Cycle Ergometry
Christina G. de Souza e Silva; Araújo,Claudio Gil S.
2015-01-01
Abstract Background: Aerobic fitness, assessed by measuring VO2max in maximum cardiopulmonary exercise testing (CPX) or by estimating VO2max through the use of equations in exercise testing, is a predictor of mortality. However, the error resulting from this estimate in a given individual can be high, affecting clinical decisions. Objective: To determine the error of estimate of VO2max in cycle ergometry in a population attending clinical exercise testing laboratories, and to propose sex-spec...
Directory of Open Access Journals (Sweden)
Bao Huy
2016-08-01
Full Text Available There are few allometric equations available for dipterocarp forests, despite the fact that this forest type covers extensive areas in tropical Southeast Asia. This study aims to develop a set of equations to estimate tree aboveground biomass (AGB in dipterocarp forests in Vietnam and to validate and compare their predictive performance with allometric equations used for dipterocarps in Indonesia and pantropical areas. Diameter at breast height (DBH, total tree height (H, and wood density (WD were used as input variables of the nonlinear weighted least square models. Akaike information criterion (AIC and residual plots were used to select the best models; while percent bias, root mean square percentage error, and mean absolute percent error were used to compare their performance to published models. For mixed-species, the best equation was AGB = 0.06203 × DBH 2.26430 × H 0.51415 × WD 0.79456 . When applied to a random independent validation dataset, the predicted values from the generic equations and the dipterocarp equations in Indonesia overestimated the AGB for different sites, indicating the need for region-specific equations. At the genus level, the selected equations were AGB = 0.03713 × DBH 2.73813 and AGB = 0.07483 × DBH 2.54496 for two genera, Dipterocarpus and Shorea, respectively, in Vietnam. Compared to the mixed-species equations, the genus-specific equations improved the accuracy of the AGB estimates. Additionally, the genus-specific equations showed no significant differences in predictive performance in different regions (e.g., Indonesia, Vietnam of Southeast Asia.
Energy Technology Data Exchange (ETDEWEB)
Verochana, Karune; Prapayasatok, Sangsom; Janhom, Apirum; Mahasantipiya, Phattaranant May; Korwanich, Narumanas [Faculty of Dentistry, Chiang Mai University, Chiang Mai (Thailand)
2016-03-15
This study assessed the accuracy of age estimates produced by a regression equation derived from lower third molar development in a Thai population. The first part of this study relied on measurements taken from panoramic radiographs of 614 Thai patients aged from 9 to 20. The stage of lower left and right third molar development was observed in each radiograph and a modified Gat score was assigned. Linear regression on this data produced the following equation: Y=9.309+1.673 mG+0.303S (Y=age; mG=modified Gat score; S=sex). In the second part of this study, the predictive accuracy of this equation was evaluated using data from a second set of panoramic radiographs (539 Thai subjects, 9 to 24 years old). Each subject's age was estimated using the above equation and compared against age calculated from a provided date of birth. Estimated and known age data were analyzed using the Pearson correlation coefficient and descriptive statistics. Ages estimated from lower left and lower right third molar development stage were significantly correlated with the known ages (r=0.818, 0.808, respectively, P≤0.01). 50% of age estimates in the second part of the study fell within a range of error of ±1 year, while 75% fell within a range of error of ±2 years. The study found that the equation tends to estimate age accurately when individuals are 9 to 20 years of age. The equation can be used for age estimation for Thai populations when the individuals are 9 to 20 years of age.
Directory of Open Access Journals (Sweden)
Xinzhi Liu
1998-01-01
Full Text Available This paper studies a class of high order delay partial differential equations. Employing high order delay differential inequalities, several oscillation criteria are established for such equations subject to two different boundary conditions. Two examples are also given.
Lp and L∞ Norm Estimates of the Cost of the Controllability for Heat Equations
Institute of Scientific and Technical Information of China (English)
Pei Dong LEI; Xu LIU; Hang GAO
2009-01-01
This paper is concerned with the bound of the cost of approximate controllability and null controllability of heat equations, i.e., the minimal Lp norm and L∞ norm of a control needed to control the system approximately or a control needed to steer the state of the system to zero. The methods we use combine observability inequalities, energy estimates for heat equations and the dual theory.
A New Entropy Formula and Gradient Estimates for the Linear Heat Equation on Static Manifold
Directory of Open Access Journals (Sweden)
Abimbola Abolarinwa
2014-08-01
Full Text Available In this paper we prove a new monotonicity formula for the heat equation via a generalized family of entropy functionals. This family of entropy formulas generalizes both Perelman’s entropy for evolving metric and Ni’s entropy on static manifold. We show that this entropy satisfies a pointwise differential inequality for heat kernel. The consequences of which are various gradient and Harnack estimates for all positive solutions to the heat equation on compact manifold.
Precision of estimating time of death by vitreous potassium--comparison of various equations.
Gamero Lucas, J J; Romero, J L; Ramos, H M; Arufe, M I; Vizcaya, M A
1992-10-01
This paper is a study of the precision of estimating the time since death comparing the equations developed by different authors. Our aim is to determine with the maximum degree of accuracy the exact time of death of the individual. We consider that the study has been fully justified by the observed differences in the results obtained from the different equations under study when the concentration of potassium in the vitreous humour was identical.
A Priori Estimates for Fractional Nonlinear Degenerate Diffusion Equations on Bounded Domains
Bonforte, Matteo; Vázquez, Juan Luis
2015-10-01
We investigate quantitative properties of the nonnegative solutions to the nonlinear fractional diffusion equation, , posed in a bounded domain, , with m > 1 for t > 0. As we use one of the most common definitions of the fractional Laplacian , 0 zero Dirichlet boundary conditions. We consider a general class of very weak solutions of the equation, and obtain a priori estimates in the form of smoothing effects, absolute upper bounds, lower bounds, and Harnack inequalities. We also investigate the boundary behaviour and we obtain sharp estimates from above and below. In addition, we obtain similar estimates for fractional semilinear elliptic equations. Either the standard Laplacian case s = 1 or the linear case m = 1 are recovered as limits. The method is quite general, suitable to be applied to a number of similar problems.
Institute of Scientific and Technical Information of China (English)
XUE Yun-feng; WANG Yu-jia; YANG Jie
2009-01-01
A new algorithm for linear instantaneous independent component analysis is proposed based on max-imizing the log-likelihood contrast function which can be changed into a gradient equation. An iterative method is introduced to solve this equation efficiently. The unknown probability density functions as well as their first and second derivatives in the gradient equation are estimated by kernel density method. Computer simulations on artificially generated signals and gray scale natural scene images confirm the efficiency and accuracy of the proposed algorithm.
Modulating functions method for parameters estimation in the fifth order KdV equation
Asiri, Sharefa M.
2017-07-25
In this work, the modulating functions method is proposed for estimating coefficients in higher-order nonlinear partial differential equation which is the fifth order Kortewegde Vries (KdV) equation. The proposed method transforms the problem into a system of linear algebraic equations of the unknowns. The statistical properties of the modulating functions solution are described in this paper. In addition, guidelines for choosing the number of modulating functions, which is an important design parameter, are provided. The effectiveness and robustness of the proposed method are shown through numerical simulations in both noise-free and noisy cases.
Healy, Martha F; Speroni, Karen Gabel; Eugenio, Kenneth R; Murphy, Patricia M
2012-04-01
Because of the renal elimination and increased risk for bleeding events at supratherapeutic doses of eptifibatide, the manufacturer recommends dosing adjustment in patients with renal dysfunction. Methods commonly used to estimate renal dysfunction in hospital settings may be inconsistent with those studied and recommended by the manufacturer. To compare hypothetical renal dosing adjustments of eptifibatide using both the recommended method and several other commonly used formulas for estimating kidney function. Sex, age, weight, height, serum creatinine, and estimated glomerular filtration rate (eGFR) were obtained retrospectively from the records of patients who received eptifibatide during a 12-month period. Renal dosing decisions were determined for each patient based on creatinine clearance (CrCl) estimates via the Cockcroft-Gault formula (CG) with actual body weight (ABW), ideal body weight (IBW) or adjusted weight (ADJW), and eGFR from the Modification of Diet in Renal Disease formula. Percent agreement and Cohen κ were calculated comparing dosing decisions for each formula to the standard CG-ABW. In this analysis of 179 patients, percent agreement as compared to CG-ABW varied (CG-IBW: 90.50%, CG-ADJW: 95.53%, and eGFR: 93.30%). All κ coefficients were categorized as good. In the 20% of patients receiving an adjusted dose by any of the methods, 68.6% could have received a dose different from that determined using the CG-ABW formula. In the patients with renal impairment (CrCl <50 mL/min) in this study, two thirds would have received an unnecessary 50% dose adjustment discordant from the manufacturer's recommendation. Because failure to adjust eptifibatide doses in patients with renal impairment has led to increased bleeding events, practitioners may be inclined to err on the side of caution. However, studies have shown that suboptimal doses of eptifibatide lead to suboptimal outcomes. Therefore, correct dosing of eptifibatide is important to both patient
An empirical comparison of estimation procedures for the von Bertalanffy growth equation
Energy Technology Data Exchange (ETDEWEB)
Vaughan, D.S.; Kanciruk, P.
1982-01-01
One non-linear and two linear methods of fitting the von Bertalanffy growth equation to length-age data were compared using Monte Carlo simulations of fish populations while varying the standard error of the length, total sample size, sampling time interval, von Bertalanffy growth parameter, and annual adult survival. The iterative, non-linear method usually produced the most accurate and precise parameter estimates. The non-linear method also provided asymptotic confidence intervals about point estimates, placed fewest constraints on data collection, and was the easiest to use. It is suggested that traditional linear solutions to the von Bertalanffy growth equation be abandoned.
Development and validation of GFR-estimating equations using diabetes, transplant and weight
Stevens, Lesley A.; Schmid, Christopher H.; Zhang, Yaping L.; Coresh, Josef; Manzi, Jane; Landis, Richard; Bakoush, Omran; Contreras, Gabriel; Genuth, Saul; Klintmalm, Goran B.; Poggio, Emilio; Rossing, Peter; Rule, Andrew D.; Weir, Matthew R.; Kusek, John; Greene, Tom; Levey, Andrew S.
2010-01-01
Background. We have reported a new equation (CKD-EPI equation) that reduces bias and improves accuracy for GFR estimation compared to the MDRD study equation while using the same four basic predictor variables: creatinine, age, sex and race. Here, we describe the development and validation of this equation as well as other equations that incorporate diabetes, transplant and weight as additional predictor variables. Methods. Linear regression was used to relate log-measured GFR (mGFR) to sex, race, diabetes, transplant, weight, various transformations of creatinine and age with and without interactions. Equations were developed in a pooled database of 10 studies [2/3 (N = 5504) for development and 1/3 (N = 2750) for internal validation], and final model selection occurred in 16 additional studies [external validation (N = 3896)]. Results. The mean mGFR was 68, 67 and 68 ml/min/ 1.73 m2 in the development, internal validation and external validation datasets, respectively. In external validation, an equation that included a linear age term and spline terms in creatinine to account for a reduction in the magnitude of the slope at low serum creatinine values exhibited the best performance (bias = 2.5, RMSE = 0.250) among models using the four basic predictor variables. Addition of terms for diabetes and transplant did not improve performance. Equations with weight showed a small improvement in the subgroup with BMI <20 kg/m2. Conclusions. The CKD-EPI equation, based on creatinine, age, sex and race, has been validated and is more accurate than the MDRD study equation. The addition of weight, diabetes and transplant does not significantly improve equation performance. PMID:19793928
Directory of Open Access Journals (Sweden)
Soghra ALIASGHARZADEH
2015-10-01
Full Text Available Background: Underweight as a public health problem in young women is associated with nutritional deficiencies, menstrual irregularity, eating disorders, reduced fertility, etc. Since resting metabolic rate (RMR is a necessary compo-nent in the development of nutrition support therapy, therefore we determined the accuracy of commonly used pre-dictive equations against RMR measured by indirect calorimetry among healthy young underweight females.Methods: This cross-sectional study was conducted on 104 underweight females aged 18-30 years old with body mass index (BMI <18.5 kg/m2 in 2013 . After collecting anthropometric data, body composition was measured by bioelec-tric impedance analysis (BIA. RMR was measured by using indirect calorimetry (FitMate™ and was estimated by 10 commonly used predictive equations. Comparisons were conducted using paired t-test. The accuracy of the RMR equations was evaluated on the basis of the percentage of subjects’ predicted RMR within 10% of measured RMR.Results: The mean BMI of subjects was 17.3±1.3 kg/m2. The measured RMR ranged 736-1490 kcal/day (mean 1084.7±175 kcal/day. Findings indicated that except Muller and Abbreviation, other equations significantly over es-timated RMR, compared to measured value (P<0.05. As an individual prediction accuracy, these predictive equations showed poor performance with the highest accuracy rate of 54.8% for Muller equation (22.1% under and 23.1% over-prediction and 43.3% for Abbreviation equation (31.7% under and 25% over-prediction, the percentage bias was 1.8% and 0.63% and RMSE was 162 and 173 kcal/d, respectively.Conclusion: Although Muller equation gave fairly acceptable prediction, more suitable new equations are needed to be developed to help better management of nutritional plans in young underweight people.
Equations for estimating bankfull channel geometry and discharge for streams in Massachusetts
Bent, Gardner C.; Waite, Andrew M.
2013-01-01
Regression equations were developed for estimating bankfull geometry—width, mean depth, cross-sectional area—and discharge for streams in Massachusetts. The equations provide water-resource and conservation managers with methods for estimating bankfull characteristics at specific stream sites in Massachusetts. This information can be used for the adminstration of the Commonwealth of Massachusetts Rivers Protection Act of 1996, which establishes a protected riverfront area extending from the mean annual high-water line corresponding to the elevation of bankfull discharge along each side of a perennial stream. Additionally, information on bankfull channel geometry and discharge are important to Federal, State, and local government agencies and private organizations involved in stream assessment and restoration projects. Regression equations are based on data from stream surveys at 33 sites (32 streamgages and 1 crest-stage gage operated by the U.S. Geological Survey) in and near Massachusetts. Drainage areas of the 33 sites ranged from 0.60 to 329 square miles (mi2). At 27 of the 33 sites, field data were collected and analyses were done to determine bankfull channel geometry and discharge as part of the present study. For 6 of the 33 sites, data on bankfull channel geometry and discharge were compiled from other studies done by the U.S. Geological Survey, Natural Resources Conservation Service of the U.S. Department of Agriculture, and the Vermont Department of Environmental Conservation. Similar techniques were used for field data collection and analysis for bankfull channel geometry and discharge at all 33 sites. Recurrence intervals of the bankfull discharge, which represent the frequency with which a stream fills its channel, averaged 1.53 years (median value 1.34 years) at the 33 sites. Simple regression equations were developed for bankfull width, mean depth, cross-sectional area, and discharge using drainage area, which is the most significant explanatory
Bayes and empirical Bayes iteration estimators in two seemingly unrelated regression equations
Institute of Scientific and Technical Information of China (English)
WANG; Lichun
2005-01-01
For a system of two seemingly unrelated regression equations given by {y1=X1β+ε1,y2=X2γ+ε2, (y1 is an m × 1 vector and y2 is an n × 1 vector, m≠ n), employing the covariance adjusted technique, we propose the parametric Bayes and empirical Bayes iteration estimator sequences for regression coefficients. We prove that both the covariance matrices converge monotonically and the Bayes iteration estimator squence is consistent as well. Based on the mean square error (MSE) criterion, we elaborate the superiority of empirical Bayes iteration estimator over the Bayes estimator of single equation when the covariance matrix of errors is unknown. The results obtained in this paper further show the power of the covariance adjusted approach.
Error estimates of H1-Galerkin mixed finite element method for Schr(o)dinger equation
Institute of Scientific and Technical Information of China (English)
LIU Yang; LI Hong; WANG Jin-feng
2009-01-01
An H1-Galerkin mixed finite element method is discussed for a class of second order SchrSdinger equation. Optimal error estimates of semidiscrete schemes are derived for problems in one space dimension. At the same time, optimal error estimates are derived for fully discrete schemes. And it is showed that the H1-Galerkin mixed finite element approximations have the same rate of convergence as in the classical mixed finite element methods without requiring the LBB consistency condition.
Naz, Hafeeza; Mushtaq, Kinza; Butt, Bilal Azeem; Khawaja, Khadija Irfan
2017-01-01
To compare three different body fats estimation equations using skin fold measurements with bioelectrical impedance analysis. A total of 130 subjects were included from Department of Endocrinology and Metabolism, Services Hospital, Lahore from 1(st) April 2016 to 30(th) Sep. 2016. The triceps, biceps, subscapular, chest, thigh, abdominal, suprailiac skinfold thickness of the subjects was measured with skin-fold calipers (Harpenden) on non-dominant side. The percentage fat mass (%FM) predicted by using each skin-fold-thickness equations namely Durnin & Womersley, Jackson & Pollock and Sloan was compared with %FM measured using a bioelectrical impedance analyzer (BIA). The mean age of subjects was 48.75±10.7 years, mean BMI was 29.08±6.09 kg/m(2). The mean %FM calculated by Durnin & Womersley (32.408±0.584), Jackson & Pollock (24.658±0.527), Sloan (20.40±0.545). The %FM by BIA was 38.182±0.529. All three equations showed positive correlation but underestimated %FM as compared to BIA. All three BF estimation equations underestimate body fat percentage compared to BIA. Among the three, Durnin & Womersley equation shows best positive correlation and hence it can be used for estimation of percentage fat mass as an alternate to BIA.
Selistre, Luciano; Rabilloud, Muriel; Cochat, Pierre; de Souza, Vandréa; Iwaz, Jean; Lemoine, Sandrine; Beyerle, Françoise; Poli-de-Figueiredo, Carlos E; Dubourg, Laurence
2016-03-01
Estimating kidney glomerular filtration rate (GFR) is of utmost importance in many clinical conditions. However, very few studies have evaluated the performance of GFR estimating equations over all ages and degrees of kidney impairment. We evaluated the reliability of two major equations for GFR estimation, the CKD-EPI and Schwartz equations, with urinary clearance of inulin as gold standard. The study included 10,610 participants referred to the Renal and Metabolic Function Exploration Unit of Edouard Herriot Hospital (Lyon, France). GFR was measured by urinary inulin clearance (only first measurement kept for analysis) then estimated with isotope dilution mass spectrometry (IDMS)-traceable CKD-EPI and Schwartz equations. The participants' ages ranged from 3 to 90 y, and the measured GFRs from 3 to 160 ml/min/1.73 m2. A linear mixed-effects model was used to model the bias (mean ratio of estimated GFR to measured GFR). Equation reliability was also assessed using precision (interquartile range [IQR] of the ratio) and accuracy (percentage of estimated GFRs within the 10% [P10] and 30% [P30] limits above and below the measured GFR). In the whole sample, the mean ratio with the CKD-EPI equation was significantly higher than that with the Schwartz equation (1.17 [95% CI 1.16; 1.18] versus 1.08 [95% CI 1.07; 1.09], p Schwartz equation were closer to 1 than the mean ratios with the CKD-EPI equation whatever the age class (1.02 [95% CI 1.01; 1.03] versus 1.15 [95% CI 1.13; 1.16], p Schwartz equation had a better precision and was also more accurate than the CKD-EPI equation at GFR values under 60 ml/min/1.73 m2 (IQR: 0.32 [95% CI 0.28; 0.33] versus 0.40 [95% CI 0.36; 0.44]; P30: 81.4 [95% CI 78.1; 84.7] versus 63.8 [95% CI 59.7; 68.0]) and also at GFR values of 60-89 ml/min/1.73 m2. In all patients aged ≥65 y, the CKD-EPI equation performed better than the Schwartz equation (IQR: 0.33 [95% CI 0.31; 0.34] versus 0.40 [95% CI 0.38; 0.41]; P30: 77.6 [95% CI 75.7; 79
Nam, Vu Thanh; van Kuijk, Marijke; Anten, Niels P R
2016-01-01
Allometric regression models are widely used to estimate tropical forest biomass, but balancing model accuracy with efficiency of implementation remains a major challenge. In addition, while numerous models exist for aboveground mass, very few exist for roots. We developed allometric equations for a
Estimation of Velocity Profile Based on Chiu’s Equation in Width of Channels
Directory of Open Access Journals (Sweden)
Saman Nikmehr
2010-08-01
Full Text Available Distribution of velocity in channel is one of the most parameters for solution of hydraulic problems. Determination of energy coefficient, momentum and distribution of sediment concentration depend on distribution of velocity profile. The entropy parameter of a channel section can be determined from the relation between the mean and maximum velocities. A technique has been developed to determine a velocity profile on a single vertical passing through the point of maximum velocity in a channel cross section. This method is a way in order to quick and cheap estimating of velocity distribution with high accuracy in channels. So that in this research the power estimation of Chiu method base on entropy concept was determined. Also Chiu’s equation that is based on entropy concept and probability domain, has compared with logarithmic and exponential equations to estimation of velocity profile in width of channel in various depths. The results show that Chiu’s equation better than logarithmic and exponential equations to estimation of velocity profile in width of channel.
Institute of Scientific and Technical Information of China (English)
2008-01-01
In this paper,we investigate the Legendre Galerkin spectral approximation of quadratic optimal control problems governed by parabolic equations.A spectral approximation scheme for the parabolic optimal control problem is presented.We obtain a posteriori error estimates of the approximated solutions for both the state and the control.
A POSTERIORI ERROR ESTIMATE OF THE DSD METHOD FOR FIRST-ORDER HYPERBOLIC EQUATIONS
Institute of Scientific and Technical Information of China (English)
康彤; 余德浩
2002-01-01
A posteriori error estimate of the discontinuous-streamline diffusion method for first-order hyperbolic equations was presented, which can be used to adjust space mesh reasonably. A numerical example is given to illustrate the accuracy and feasibility of this method.
SUPERCONVERGENCE AND A POSTERIORI ERROR ESTIMATES FOR BOUNDARY CONTROL GOVERNED BY STOKES EQUATIONS
Institute of Scientific and Technical Information of China (English)
Hui-po Liu; Ning-ning Yan
2006-01-01
In this paper, the superconvergence results are derived for a class of boundary control problems governed by Stokes equations. We derive superconvergence results for both the control and the state approximation. Base on superconvergence results, we obtain asymptotically exact a posteriori error estimates.
A New Equation to Estimate Muscle Mass from Creatinine and Cystatin C.
Directory of Open Access Journals (Sweden)
Sun-wook Kim
Full Text Available With evaluation for physical performance, measuring muscle mass is an important step in detecting sarcopenia. However, there are no methods to estimate muscle mass from blood sampling.To develop a new equation to estimate total-body muscle mass with serum creatinine and cystatin C level, we designed a cross-sectional study with separate derivation and validation cohorts. Total body muscle mass and fat mass were measured using dual-energy x-ray absorptiometry (DXA in 214 adults aged 25 to 84 years who underwent physical checkups from 2010 to 2013 in a single tertiary hospital. Serum creatinine and cystatin C levels were also examined.Serum creatinine was correlated with muscle mass (P < .001, and serum cystatin C was correlated with body fat mass (P < .001 after adjusting glomerular filtration rate (GFR. After eliminating GFR, an equation to estimate total-body muscle mass was generated and coefficients were calculated in the derivation cohort. There was an agreement between muscle mass calculated by the novel equation and measured by DXA in both the derivation and validation cohort (P < .001, adjusted R2 = 0.829, β = 0.95, P < .001, adjusted R2 = 0.856, β = 1.03, respectively.The new equation based on serum creatinine and cystatin C levels can be used to estimate total-body muscle mass.
Nam, Vu Thanh; Kuijk, Van Marijke; Anten, Niels P.R.
2016-01-01
Allometric regression models are widely used to estimate tropical forest biomass, but balancing model accuracy with efficiency of implementation remains a major challenge. In addition, while numerous models exist for aboveground mass, very few exist for roots. We developed allometric equations fo
THE INTERIOR ESTIMATE FOR THE SOLUTION OF THE DEGENERATE MONGE-AMPERE EQUATION
Institute of Scientific and Technical Information of China (English)
Bao Jiguang
2000-01-01
By applying Krylov maximum principle of elliptic operators on the manifolds, we get the interior second derivative estimates for the solutions of the degenerate Monge-Ampere equations in the plane convex domains, under the weaker conditions. Our method is much simpler than the previous ones.
Klein, Andreas G.; Muthen, Bengt O.
2007-01-01
In this article, a nonlinear structural equation model is introduced and a quasi-maximum likelihood method for simultaneous estimation and testing of multiple nonlinear effects is developed. The focus of the new methodology lies on efficiency, robustness, and computational practicability. Monte-Carlo studies indicate that the method is highly…
A multivariate family-based association test using generalized estimating equations : FBAT-GEE
Lange, C; Silverman, SK; Xu, [No Value; Weiss, ST; Laird, NM
2003-01-01
In this paper we propose a multivariate extension of family-based association tests based on generalized estimating equations. The test can be applied to multiple phenotypes and to phenotypic data obtained in longitudinal studies without making any distributional assumptions for the phenotypic obser
Optimal error estimates for Fourier spectral approximation of the generalized KdV equation
Institute of Scientific and Technical Information of China (English)
Zhen-guo DENG; He-ping MA
2009-01-01
A Fourier spectral method for the generalized Korteweg-de Vrics equation with periodic boundary conditions is analyzed, and a corresponding optimal error esti-mate in L2-norm is obtained. It improves the result presented by Maday and Quarteroni. A modified Fourier pseudospectral method is also presented, with the same convergence properties as the Fourier spectral method.
Zhao, Yongling; Hu, Eric; Blazewicz, Antoni
2012-02-01
This paper presents isosteric-based adsorption equilibrium tests of three activated carbon samples with methanol as an adsorbate. Experimental data was fitted into Langmuir equation, Freundlich equation and Dubinin-Astakov (D-A) equation, respectively. The fitted adsorption equations were compared in terms of agreement with experimental data. Moreover, equation format's impacts on calculation of the coefficient of performance (COP) and refrigeration capacity of an adsorption refrigeration system was analyzed. In addition, the sensitivity of each parameter in each adsorption equation format to the estimation of cycle's COP and refrigeration capacity was investigated. It was found that the D-A equation is the best form for presenting the adsorptive property of a carbon-methanol working pair. The D-A equation is recommended for estimating thermal performance of an adsorption refrigeration system because simulation results obtained using the D-A equation are less sensitive to errors of experimentally determined D-A equation's parameters.
Energy Technology Data Exchange (ETDEWEB)
Holden, Helge; Karlsen, Kenneth H.; Lie, Knut-Andreas
1999-10-01
We present and analyze a numerical method for the solution of a class of scalar, multi-dimensional, nonlinear degenerate convection-diffusion equations. The method is based on operator splitting to separate the convective and the diffusive terms in the governing equation. The nonlinear, convective part is solved using front tracking and dimensional splitting, while the nonlinear diffusion equation is solved by a suitable difference scheme. We verify L{sup 1} compactness of the corresponding set of approximate solutions and derive precise entropy estimates. In particular, these results allow us to pass to the limit in our approximations and recover an entropy solution of the problem in question. The theory presented covers a large class of equations. Important subclasses are hyperbolic conservation laws, porous medium type equations, two-phase reservoir flow equations, and strongly degenerate equations coming from the recent theory of sedimentation-consolidation processes. A thorough numerical investigation of the method analyzed in this paper (and similar methods) is presented in a companion paper. (author)
Sugiyama, K; Isogai, K; Toyama, A; Satoh, H; Saito, K; Nakagawa, Y; Tasaki, M; Takahashi, K; Saito, N; Hirano, T
2009-10-01
Lymphocyte immunosuppressant sensitivity test (LIST) is useful for predicting the pharmacological efficacy of immunosuppressive agents. In this study, the pharmacological efficacy of cyclosporine was estimated by LIST before and after renal transplantation. Lymphocyte immunosuppressant sensitivity test was performed by the 3-(4,5-dimethylthiazol-2-yl)-2,5diphenyltetrazolium bromide (MTT) assay before and at 1, 3, and 12 months after transplantation in 19 consecutive renal transplant recipients. There was wide intersubject variability in cyclosporine IC50 before transplantation [Mean (SD) of 593.9 (1067.6) ng/mL]. This variability worsened 1 month after transplantation [525.7 (1532.7) ng/mL] but decreased at 3 months (193.5 (347.9) ng/mL) and 12 months (75.4 (95.4) ng/mL). In this small study, observed differences in IC50 values for the individual subjects at various time intervals was not associated with the occurrence of rejection, graft loss, and infection episodes. Lymphocyte sensitivity to cyclosporine assessed by the LIST assay showed a high level of inter-subject variability particularly before and 1 month after transplantation. The observed difference in IC50 values was not associated with clinical outcome in this small study.
Sex-Specific Equations to Estimate Maximum Oxygen Uptake in Cycle Ergometry.
Souza e Silva, Christina G de; Araújo, Claudio Gil S
2015-10-01
Aerobic fitness, assessed by measuring VO2max in maximum cardiopulmonary exercise testing (CPX) or by estimating VO2max through the use of equations in exercise testing, is a predictor of mortality. However, the error resulting from this estimate in a given individual can be high, affecting clinical decisions. To determine the error of estimate of VO2max in cycle ergometry in a population attending clinical exercise testing laboratories, and to propose sex-specific equations to minimize that error. This study assessed 1715 adults (18 to 91 years, 68% men) undertaking maximum CPX in a lower limbs cycle ergometer (LLCE) with ramp protocol. The percentage error (E%) between measured VO2max and that estimated from the modified ACSM equation (Lang et al. MSSE, 1992) was calculated. Then, estimation equations were developed: 1) for all the population tested (C-GENERAL); and 2) separately by sex (C-MEN and C-WOMEN). Measured VO2max was higher in men than in WOMEN: -29.4 ± 10.5 and 24.2 ± 9.2 mL.(kg.min)-1 (p VO2max [in mL.(kg.min)-1] were: C-GENERAL = [final workload (W)/body weight (kg)] x 10.483 + 7; C-MEN = [final workload (W)/body weight (kg)] x 10.791 + 7; and C-WOMEN = [final workload (W)/body weight (kg)] x 9.820 + 7. The E% for MEN was: -3.4 ± 13.4% (modified ACSM); 1.2 ± 13.2% (C-GENERAL); and -0.9 ± 13.4% (C-MEN) (p VO2max by use of sex-specific equations was reduced, but not eliminated, in exercise tests on LLCE.
Institute of Scientific and Technical Information of China (English)
Wei Gong; Ningning Yan
2009-01-01
In this paper.we discuss the a posteriori error estimate of the finite element approximation for the boundary control problems governed by the parabolic partial differential equations.Three different a posteriori error estimators are provided for the parabolic boundary control problems with the observations of the distributed state.the boundary state and the final state.It is proven that these estimators are reliable bounds of the finite element approximation errors,which can be used as the indicators of the mesh refinement in adaptive finite element methods.
An estimating equation for parametric shared frailty models with marginal additive hazards
DEFF Research Database (Denmark)
Pipper, Christian Bressen; Martinussen, Torben
2004-01-01
Multivariate failure time data arise when data consist of clusters in which the failure times may be dependent. A popular approach to such data is the marginal proportional hazards model with estimation under the working independence assumption. In some contexts, however, it may be more reasonable...... to use the marginal additive hazards model. We derive asymptotic properties of the Lin and Ying estimators for the marginal additive hazards model for multivariate failure time data. Furthermore we suggest estimating equations for the regression parameters and association parameters in parametric shared...
Body composition in elderly people: effect of criterion estimates on predictive equations
Energy Technology Data Exchange (ETDEWEB)
Baumgartner, R.N.; Heymsfield, S.B.; Lichtman, S.; Wang, J.; Pierson, R.N. Jr. (Wright State Univ. School of Medicine, Dayton, OH (USA))
1991-06-01
The purposes of this study were to determine whether there are significant differences between two- and four-compartment model estimates of body composition, whether these differences are associated with aqueous and mineral fractions of the fat-free mass (FFM); and whether the differences are retained in equations for predicting body composition from anthropometry and bioelectric resistance. Body composition was estimated in 98 men and women aged 65-94 y by using a four-compartment model based on hydrodensitometry, {sup 3}H{sub 2}O dilution, and dual-photon absorptiometry. These estimates were significantly different from those obtained by using Siri's two-compartment model. The differences were associated significantly (P less than 0.0001) with variation in the aqueous fraction of FFM. Equations for predicting body composition from anthropometry and resistance, when calibrated against two-compartment model estimates, retained these systematic errors. Equations predicting body composition in elderly people should be calibrated against estimates from multicompartment models that consider variability in FFM composition.
Mathematical modelling of transport of a non-diffusible indicator to estimate renal blood supply
Energy Technology Data Exchange (ETDEWEB)
Gelfand, I.N.; Narkevich, V.Y.
1985-01-01
A new method is recommended to interpret the results in radionuclide studies of renal blood flow with the mathematical modelling of transport of a non-diffusible indicator in the blood vessels. The analytic proportions are ascertained between mean transit time of indicator, mean retention time (both at impulse influence and at occurence of any signal at the input) for different forms of transport function, and impulse-shaped retention function of the studied physiological system. By means of external measuring of radioactivity this allows to estimate the mean transit time of the indicator by the studied element of hemodynamics, an index, used in classically physiological studies. The recommended system of physiological indices describes the statistic and dynamic parameters of the vessel network in each kidney adequately. The use of this method showed its efficiency on principle in 7 healthy persons and in 4 patients with clinically manifest kidney diseases. (author).
Directory of Open Access Journals (Sweden)
Pedro L. Valencia
2017-04-01
Full Text Available We provide initial rate data from enzymatic reaction experiments and tis processing to estimate the kinetic parameters from the substrate uncompetitive inhibition equation using the median method published by Eisenthal and Cornish-Bowden (Cornish-Bowden and Eisenthal, 1974; Eisenthal and Cornish-Bowden, 1974. The method was denominated the direct linear plot and consists in the calculation of the median from a dataset of kinetic parameters Vmax and Km from the Michaelis–Menten equation. In this opportunity we present the procedure to applicate the direct linear plot to the substrate uncompetitive inhibition equation; a three-parameter equation. The median method is characterized for its robustness and its insensibility to outlier. The calculations are presented in an Excel datasheet and a computational algorithm was developed in the free software Python. The kinetic parameters of the substrate uncompetitive inhibition equation Vmax, Km and Ks were calculated using three experimental points from the dataset formed by 13 experimental points. All the 286 combinations were calculated. The dataset of kinetic parameters resulting from this combinatorial was used to calculate the median which corresponds to the statistic estimator of the real kinetic parameters. A comparative statistical analyses between the median method and the least squares was published in Valencia et al. [3].
Valencia, Pedro L; Astudillo-Castro, Carolina; Gajardo, Diego; Flores, Sebastián
2017-04-01
We provide initial rate data from enzymatic reaction experiments and tis processing to estimate the kinetic parameters from the substrate uncompetitive inhibition equation using the median method published by Eisenthal and Cornish-Bowden (Cornish-Bowden and Eisenthal, 1974; Eisenthal and Cornish-Bowden, 1974). The method was denominated the direct linear plot and consists in the calculation of the median from a dataset of kinetic parameters Vmax and Km from the Michaelis-Menten equation. In this opportunity we present the procedure to applicate the direct linear plot to the substrate uncompetitive inhibition equation; a three-parameter equation. The median method is characterized for its robustness and its insensibility to outlier. The calculations are presented in an Excel datasheet and a computational algorithm was developed in the free software Python. The kinetic parameters of the substrate uncompetitive inhibition equation Vmax , Km and Ks were calculated using three experimental points from the dataset formed by 13 experimental points. All the 286 combinations were calculated. The dataset of kinetic parameters resulting from this combinatorial was used to calculate the median which corresponds to the statistic estimator of the real kinetic parameters. A comparative statistical analyses between the median method and the least squares was published in Valencia et al. [3].
Equations for estimating muscle fiber stress in the left ventricular wall.
Rabben, S I; Irgens, F; Angelsen, B
1999-01-01
Left ventricular muscle fiber stress is an important parameter in cardiac energetics. Hence, we developed equations for estimating regional fiber stresses in rotationally symmetric chambers, and equatorial and apical fiber stresses in prolate spheroidal chambers. The myocardium was modeled as a soft incompressible material embedding muscle fibers that support forces only in their longitudinal direction. A thin layer of muscle fibers then contributes with a pressure increment determined by the fiber stress and curvature. The fiber curvature depends on the orientation of the fibers, which varies continuously across the wall. However, by assuming rotational symmetry about the long axis of the ventricle and including a longitudinal force balance, we obtained equations where fiber stress is completely determined by the principal curvatures of the middle wall surface, wall thickness, and cavity pressure. The equations were validated against idealized prolate spheroidal chambers, whose wall thicknesses are such that the fiber stress is uniform from the equator to the apex. Because the apex is free to rotate, the resultant moment about the long axis of the LV must be zero. By using this constraint together with our fiber-stress equations, we were able to estimate a muscle fiber orientation distribution across the wall that was in qualitative agreement with published measurements.
Approximate Damped Oscillatory Solutions for Compound KdV-Burgers Equation and Their Error Estimates
Institute of Scientific and Technical Information of China (English)
Wei-guo ZHANG; Yan ZHAO; Xiao-yan TENG
2012-01-01
In this paper,we focus on studying approximate solutions of damped oscillatory solutions of the compound KdV-Burgers equation and their error estimates.We employ the theory of planar dynamical systems to study traveling wave solutions of the compound KdV-Burgers equation.We obtain some global phase portraits under different parameter conditions as well as the existence of bounded traveling wave solutions.Furthermore,we investigate the relations between the behavior of bounded traveling wave solutions and the dissipation coefficient r of the equation.We obtain two critical values of r,and find that a bounded traveling wave appears as a kink profile solitary wave if |r| is greater than or equal to some critical value,while it appears as a damped oscillatory wave if |r| is less than some critical value.By means of analysis and the undetermined coefficients method,we find that the compound KdV-Burgers equation only has three kinds of bell profile solitary wave solutions without dissipation.Based on the above discussions and according to the evolution relations of orbits in the global phase portraits,we obtain all approximate damped oscillatory solutions by using the undetermined coefficients method.Finally,using the homogenization principle,we establish the integral equations reflecting the relations between exact solutions and approximate solutions of damped oscillatory solutions.Moreover,we also give the error estimates for these approximate solutions.
Bateni, S. M.; Michalik, T.; Multsch, S.; Breuer, L.
2015-12-01
Crop evapotranspiration (ETc) is a key component of water resources management in irrigation of farmlands as it determines the crop water consumption. Numerous methods have been used to estimate ETc for scheduling irrigation and evaluating the soil water balance. However, there is a significant difference in ETc estimates from various models, which leads to a large uncertainty in the soil water balance, crop water consumption, and irrigation scheduling. In this study, several commonly-used ETc equations (Turc, Priestley-Taylor, Hargreaves-Samani, Penman-Monteith) are compared with the variational data assimilation approach (VDA) of Bateni et al. (2013). The ETc equations initially estimate the reference evapotranspiration (ETo), which is the evapotranspiration from a healthy and actively-transpiring grass field with ample water in the soil. Thereafter, ETc is calculated by multiplying ETo by the crop coefficient (Kc), which accounts for the crop type and soil water stress. To properly apply the Kc to non-standard conditions, a daily water balance estimation for the root zone is required, which is done by two soil water budget models (Cropwat, Hydrus-1D) that compute incoming and outgoing water flows in the soil profile. In contrast to these methods that estimate ETc in two steps, the VDA approach directly predicts ETc by assimilating sequences of land surface temperature into the heat diffusion equation and thus it is expected to provide more accurate ETc estimates. All approaches are applied over three cropland sites namely, Bondville, Fermi, and Mead in the summer of 2006 and 2007. These sites are part of the AmeriFlux network and provide a wide variety of hydrological conditions. The results show that the variational data assimilation approach performs better compared to other equations.
Sex-Specific Equations to Estimate Maximum Oxygen Uptake in Cycle Ergometry
Directory of Open Access Journals (Sweden)
Christina G. de Souza e Silva
2015-01-01
Full Text Available Abstract Background: Aerobic fitness, assessed by measuring VO2max in maximum cardiopulmonary exercise testing (CPX or by estimating VO2max through the use of equations in exercise testing, is a predictor of mortality. However, the error resulting from this estimate in a given individual can be high, affecting clinical decisions. Objective: To determine the error of estimate of VO2max in cycle ergometry in a population attending clinical exercise testing laboratories, and to propose sex-specific equations to minimize that error. Methods: This study assessed 1715 adults (18 to 91 years, 68% men undertaking maximum CPX in a lower limbs cycle ergometer (LLCE with ramp protocol. The percentage error (E% between measured VO2max and that estimated from the modified ACSM equation (Lang et al. MSSE, 1992 was calculated. Then, estimation equations were developed: 1 for all the population tested (C-GENERAL; and 2 separately by sex (C-MEN and C-WOMEN. Results: Measured VO2max was higher in men than in WOMEN: -29.4 ± 10.5 and 24.2 ± 9.2 mL.(kg.min-1 (p < 0.01. The equations for estimating VO2max [in mL.(kg.min-1] were: C-GENERAL = [final workload (W/body weight (kg] x 10.483 + 7; C-MEN = [final workload (W/body weight (kg] x 10.791 + 7; and C-WOMEN = [final workload (W/body weight (kg] x 9.820 + 7. The E% for MEN was: -3.4 ± 13.4% (modified ACSM; 1.2 ± 13.2% (C-GENERAL; and -0.9 ± 13.4% (C-MEN (p < 0.01. For WOMEN: -14.7 ± 17.4% (modified ACSM; -6.3 ± 16.5% (C-GENERAL; and -1.7 ± 16.2% (C-WOMEN (p < 0.01. Conclusion: The error of estimate of VO2max by use of sex-specific equations was reduced, but not eliminated, in exercise tests on LLCE.
Deng, Fang; Finer, Gal; Haymond, Shannon; Brooks, Ellen; Langman, Craig B.
2014-01-01
Estimates of glomerular filtration rate (eGFR) have become popular in clinical medicine as an alternative to measuring GFR (mGFR) but there are few studies comparing them in clinical practice. We determined mGFR by iohexol clearance in 81 consecutive children in routine practice and calculated eGFR from 14 standard equations using serum creatinine, cystatin C, and urea nitrogen that were collected at the time of the mGFR procedure. Non-parametric Wilcoxon test, Spearman Correlation, Bland–Altman analysis, bias (median difference) and accuracy (P15, P30) were used to compare mGFR to eGFR. For the entire study group, the mGFR was 77.9±38.8mL/min/1.73 m2. Eight of the 14 estimating equations demonstrated values without a significant difference from the mGFR value and demonstrated a lower bias in Bland–Altman analysis. Three of these eight equations based on a combination of creatinine and cystatin C, (Schwartz et al. 2009, 2012; Chehade et al.), had the highest accuracy with approximately 60% of P15 and 80% of P30. In 10 patients with a single kidney, seven with kidney transplant, and 11 additional children with short stature, values of the three equations had low bias and no significant difference when compared with mGFR. In conclusion, the three equations that employed cystatin C, creatinine, and growth parameters performed in a superior manner over univariate equations based on either creatinine or cystatin C, and also had good applicability in specific pediatric patients with single kidneys, those with a kidney transplant, and/or short stature. Thus, we suggest that eGFR calculations in pediatric clinical practice employ only a multivariate equation. PMID:25445208
Rosenblatt, Marcus; Timmer, Jens; Kaschek, Daniel
2016-01-01
Ordinary differential equation models have become a wide-spread approach to analyze dynamical systems and understand underlying mechanisms. Model parameters are often unknown and have to be estimated from experimental data, e.g., by maximum-likelihood estimation. In particular, models of biological systems contain a large number of parameters. To reduce the dimensionality of the parameter space, steady-state information is incorporated in the parameter estimation process. For non-linear models, analytical steady-state calculation typically leads to higher-order polynomial equations for which no closed-form solutions can be obtained. This can be circumvented by solving the steady-state equations for kinetic parameters, which results in a linear equation system with comparatively simple solutions. At the same time multiplicity of steady-state solutions is avoided, which otherwise is problematic for optimization. When solved for kinetic parameters, however, steady-state constraints tend to become negative for particular model specifications, thus, generating new types of optimization problems. Here, we present an algorithm based on graph theory that derives non-negative, analytical steady-state expressions by stepwise removal of cyclic dependencies between dynamical variables. The algorithm avoids multiple steady-state solutions by construction. We show that our method is applicable to most common classes of biochemical reaction networks containing inhibition terms, mass-action and Hill-type kinetic equations. Comparing the performance of parameter estimation for different analytical and numerical methods of incorporating steady-state information, we show that our approach is especially well-tailored to guarantee a high success rate of optimization.
Energy Technology Data Exchange (ETDEWEB)
Rupšys, P. [Aleksandras Stulginskis University, Studenų g. 11, Akademija, Kaunas district, LT – 53361 Lithuania (Lithuania)
2015-10-28
A system of stochastic differential equations (SDE) with mixed-effects parameters and multivariate normal copula density function were used to develop tree height model for Scots pine trees in Lithuania. A two-step maximum likelihood parameter estimation method is used and computational guidelines are given. After fitting the conditional probability density functions to outside bark diameter at breast height, and total tree height, a bivariate normal copula distribution model was constructed. Predictions from the mixed-effects parameters SDE tree height model calculated during this research were compared to the regression tree height equations. The results are implemented in the symbolic computational language MAPLE.
Rupšys, P.
2015-10-01
A system of stochastic differential equations (SDE) with mixed-effects parameters and multivariate normal copula density function were used to develop tree height model for Scots pine trees in Lithuania. A two-step maximum likelihood parameter estimation method is used and computational guidelines are given. After fitting the conditional probability density functions to outside bark diameter at breast height, and total tree height, a bivariate normal copula distribution model was constructed. Predictions from the mixed-effects parameters SDE tree height model calculated during this research were compared to the regression tree height equations. The results are implemented in the symbolic computational language MAPLE.
Set-membership state estimation framework for uncertain linear differential-algebraic equations
Zhuk, Serhiy
2008-01-01
We investigate a problem of state estimation for the dynamical system described by the linear operator equation with unknown parameters in Hilbert space. We present explicit expressions for linear minimax estimation and error provided that any pair of uncertain parameters belongs to the quadratic bounding set. As an application of the introduced approach we introduce a notion of minimax directional observability and index of non-causality for linear noncausal DAEs. Application of these notions to the problem of state estimation for the linear uncertain noncausal DAEs allows to construct the state estimation in the form of the recursive minimax filter. A numerical example of the state estimation for 3D non-causal descriptor system is presented.
Directory of Open Access Journals (Sweden)
Carlos Chiurchiu
2007-04-01
Full Text Available La creatinina sérica es un marcador poco sensible para identificar reducciones leves del índice de filtración glomerular (IFG; por ello resulta de gran importancia clínica disponer de métodos alternativos para estimar la función renal. Con este objetivo estudiamos la función renal de 41 pacientes -grupo completo y divididos según la creatinina sérica (≤ 1.2 mg/dl o mayores- usando el clearance de creatinina modificado con cimetidina (Clcrc como aproximación al IFG, las ecuaciones de Larsson y Hoek que incluyen el uso de cistatina C sérica y las tradicionales fórmulas de Cockroft-Gault y MDRD abreviada. En el grupo completo de pacientes y especialmente en aquellos con creatinina sérica ≤1.2 mg/dl -con reducción de la función renal: Clcrc: 62.01 ± 17.33 ml/min/1.73 m²-, las ecuaciones de Larsson y Hoek mostraron mejores correlaciones y menores diferencias promedio respecto a las fórmulas basadas en la creatinina sérica. La ecuación MDRD abreviada mostró buen rendimiento sólo en el grupo con evidente alteración de la función renal (creatinina sérica > 1.2 mg/dl. Concluimos que en pacientes con diferentes estadios de función renal, las fórmulas que emplean la cistatina C sérica detectan la reducción del IFG más precozmente respecto a aquellas basadas en la creatinina sérica.Serum creatinine is an insensitive marker to identify early changes in glomerular filtration rate (GFR, for this reason alternative methods to estimate renal function result of great clinical importance. Forty-one patients were studied using creatinine clearance modified with cimetidina (Clcrc as surrogate of GFR, cystatin C-based equations (i.e. Larsson and Hoek formulas, Cockroft-Gault and MDRD abbreviated equations. In the whole group, as well as in those patients with serum creatinine ≤1.2 mg/dl -but reduced renal function: Clcrc 62.01 ± 17.33 ml/min/1.73 m²-, Larsson and Hoek equations showed higher correlations and lower bias than
Directory of Open Access Journals (Sweden)
Juliana Cordeiro Dias Rodrigues
2013-02-01
Full Text Available Estabelecer as necessidades energéticas de pacientes com doença renal crônica é importante para que se possam tratar os distúrbios nutricionais encontrados nessa população. Segundo os guias de condutas voltados ao cuidado nutricional de pacientes com essa doença, a recomendação energética pode variar entre 30 e 40kcal/kg/dia. Contudo, trabalhos que avaliaram os componentes do gasto energético nos pacientes com doença renal crônica sugerem que as necessidades energéticas dessa população podem diferir do valor recomendado acima, a depender da condição clínica (presença de comorbidades, da modalidade de tratamento empregado e do nível de atividade física. Dessa forma, o presente trabalho tem como objetivo fazer uma revisão dos estudos sobre o gasto energético de pacientes com doença renal crônica, com o intuito de abordar as seguintes questões: (1 as atuais recomendações de energia para pacientes com doença renal crônica estão adequadas? (2 qual equação de predição poderia ser empregada para estimar as necessidades energéticas desse grupo de pacientes? Assim, esta revisão busca auxiliar o nutricionista ao estimar as necessidades energéticas de pacientes com doença renal crônica.Estimating the energy requirement of patients with chronic kidney disease is highly important for treating the nutritional disorders often seen in this population. According to the specific guidelines for patients with chronic kidney disease, the currently recommended daily energy intake varies from 30 to 40kcal/kg/day. However, studies that investigated energy expenditure components of patients with chronic kidney disease suggested that the energy requirement may differ from the one proposed earlier, depending on overall clinical condition (i.e. presence of comorbidities, treatment modality and level of physical activity. With this perspective in mind, the present study aims to review the studies assessing energy expenditure
Coresh, J.; Turin, T.C.; Matsushita, K.; Sang, Y.; Ballew, S.H.; Appel, L.J.; Arima, H.; Chadban, S.J.; Cirillo, M.; Djurdjev, O.; Green, J.A.; Heine, G.H.; Inker, L.A.; Irie, F.; Ishani, A.; Ix, J.H.; Kovesdy, C.P.; Marks, A.; Ohkubo, T.; Shalev, V.; Shankar, A.; Wen, C.P.; Jong, P.E. de; Iseki, K.; Stengel, B.; Gansevoort, R.T.; Levey, A.S.; Wetzels, J.F.M.
2014-01-01
IMPORTANCE: The established chronic kidney disease (CKD) progression end point of end-stage renal disease (ESRD) or a doubling of serum creatinine concentration (corresponding to a change in estimated glomerular filtration rate [GFR] of -57% or greater) is a late event. OBJECTIVE: To characterize th
Coresh, Josef; Turin, Tanvir Chowdhury; Matsushita, Kunihiro; Sang, Yingying; Ballew, Shoshana H.; Appel, Lawrence J.; Arima, Hisatomi; Chadban, Steven J.; Cirillo, Massimo; Djurdjev, Ognjenka; Green, Jamie A.; Heine, Gunnar H.; Inker, Lesley A.; Irie, Fujiko; Ishani, Areef; Ix, Joachim H.; Kovesdy, Csaba P.; Marks, Angharad; Ohkubo, Takayoshi; Shalev, Varda; Shankar, Anoop; Wen, Chi Pang; de Jong, Paul E.; Iseki, Kunitoshi; Stengel, Benedicte; Gansevoort, Ron T.; Levey, Andrew S.
2014-01-01
IMPORTANCE: The established chronic kidney disease (CKD) progression end point of end-stage renal disease (ESRD) or a doubling of serum creatinine concentration (corresponding to a change in estimated glomerular filtration rate [GFR] of −57% or greater) is a late event. OBJECTIVE: To characterize th
Nitsch, D.; Grams, M.; Sang, Y.; Black, C.; Cirillo, M.; Djurdjev, O.; Iseki, K.; Jassal, S.K.; Kimm, H.; Kronenberg, F.; Oien, C.M.; Levey, A.S.; Levin, A.; Woodward, M.; Hemmelgarn, B.R.; Wetzels, J.F.
2013-01-01
OBJECTIVE: To assess for the presence of a sex interaction in the associations of estimated glomerular filtration rate and albuminuria with all-cause mortality, cardiovascular mortality, and end stage renal disease. DESIGN: Random effects meta-analysis using pooled individual participant data. SETTI
H\\"older Estimates for Singular Non-local Parabolic Equations
Kim, Sunghoon
2011-01-01
In this paper, we establish local H\\"older estimate for non-negative solutions of the singular equation \\eqref{eq-nlocal-PME-1} below, for $m$ in the range of exponents $(\\frac{n-2\\sigma}{n+2\\sigma},1)$. Since we have trouble in finding the local energy inequality of $v$ directly. we use the fact that the operator $(-\\La)^{\\sigma}$ can be thought as the normal derivative of some extension $v^{\\ast}$ of $v$ to the upper half space, \\cite{CS}, i.e., $v$ is regarded as boundary value of $v^{\\ast}$ the solution of some local extension problem. Therefore, the local H\\"older estimate of $v$ can be obtained by the same regularity of $v^{\\ast}$. In addition, it enables us to describe the behaviour of solution of non-local fast diffusion equation near their extinction time.
Majeed, Muhammad Usman
2017-07-19
Steady-state elliptic partial differential equations (PDEs) are frequently used to model a diverse range of physical phenomena. The source and boundary data estimation problems for such PDE systems are of prime interest in various engineering disciplines including biomedical engineering, mechanics of materials and earth sciences. Almost all existing solution strategies for such problems can be broadly classified as optimization-based techniques, which are computationally heavy especially when the problems are formulated on higher dimensional space domains. However, in this dissertation, feedback based state estimation algorithms, known as state observers, are developed to solve such steady-state problems using one of the space variables as time-like. In this regard, first, an iterative observer algorithm is developed that sweeps over regular-shaped domains and solves boundary estimation problems for steady-state Laplace equation. It is well-known that source and boundary estimation problems for the elliptic PDEs are highly sensitive to noise in the data. For this, an optimal iterative observer algorithm, which is a robust counterpart of the iterative observer, is presented to tackle the ill-posedness due to noise. The iterative observer algorithm and the optimal iterative algorithm are then used to solve source localization and estimation problems for Poisson equation for noise-free and noisy data cases respectively. Next, a divide and conquer approach is developed for three-dimensional domains with two congruent parallel surfaces to solve the boundary and the source data estimation problems for the steady-state Laplace and Poisson kind of systems respectively. Theoretical results are shown using a functional analysis framework, and consistent numerical simulation results are presented for several test cases using finite difference discretization schemes.
Borzykh, A. N.
2017-01-01
The Seidel method for solving a system of linear algebraic equations and an estimate of its convergence rate are considered. It is proposed to change the order of equations. It is shown that the method described in Faddeevs' book Computational Methods of Linear Algebra can deteriorate the convergence rate estimate rather than improve it. An algorithm for establishing the optimal order of equations is proposed, and its validity is proved. It is shown that the computational complexity of the reordering is 2 n 2 additions and (12) n 2 divisions. Numerical results for random matrices of order 100 are presented that confirm the proposed improvement.
EXPONENTIAL ESTIMATE OF SOLUTION TO STOCHASTIC FUNCTIONAL DIFFERENTIAL EQUATIONS WITH INFINITE DELAY
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
In this paper, by the Burkholder-Davis-Gundy inequality and It formula, the exponential estimate of the solution to stochastic functional differential equations with infinite delay is established in the phase space BC((-∞,0];Rd). Furthermore, the sample Lyapunov exponent of the solution is obtained, which is less than a positive constant 2√K + 65K. Moreover, a pth moment of the solution is studied.
Directory of Open Access Journals (Sweden)
Lee HyunYoung
2010-01-01
Full Text Available We analyze discontinuous Galerkin methods with penalty terms, namely, symmetric interior penalty Galerkin methods, to solve nonlinear Sobolev equations. We construct finite element spaces on which we develop fully discrete approximations using extrapolated Crank-Nicolson method. We adopt an appropriate elliptic-type projection, which leads to optimal error estimates of discontinuous Galerkin approximations in both spatial direction and temporal direction.
A Consistent Direct Method for Estimating Parameters in Ordinary Differential Equations Models
Holte, Sarah E.
2016-01-01
Ordinary differential equations provide an attractive framework for modeling temporal dynamics in a variety of scientific settings. We show how consistent estimation for parameters in ODE models can be obtained by modifying a direct (non-iterative) least squares method similar to the direct methods originally developed by Himmelbau, Jones and Bischoff. Our method is called the bias-corrected least squares (BCLS) method since it is a modification of least squares methods known to be biased. Co...
OPTIMAL ERROR ESTIMATES FOR NEDELEC EDGE ELEMENTS FOR TIME-HARMONIC MAXWELL'S EQUATIONS
Institute of Scientific and Technical Information of China (English)
Liuqiang Zhong; Shi Shu; Gabriel Wittum; Jinchao Xu
2009-01-01
In this paper, we obtain optimal error estimates in both L2-norm and H(curl)-norm for the Nedelec edge finite element approximation of the time-harmonic Maxwell's equations on a general Lipschitz domain discretized on quasi-uniform meshes. One key to our proof is to transform the L2 error estimates into the L2 estimate of a discrete divergence-free function which belongs to the edge finite element spaces, and then use the approximation of the discrete divergence-free function by the continuous divergence-free function and a duality argument for the continuous divergence-free function. For Nedelec's second type elements, we present an optimal convergence estimate which improves the best results available in the literature.
Hall, Eric Joseph
2016-12-08
We derive computable error estimates for finite element approximations of linear elliptic partial differential equations with rough stochastic coefficients. In this setting, the exact solutions contain high frequency content that standard a posteriori error estimates fail to capture. We propose goal-oriented estimates, based on local error indicators, for the pathwise Galerkin and expected quadrature errors committed in standard, continuous, piecewise linear finite element approximations. Derived using easily validated assumptions, these novel estimates can be computed at a relatively low cost and have applications to subsurface flow problems in geophysics where the conductivities are assumed to have lognormal distributions with low regularity. Our theory is supported by numerical experiments on test problems in one and two dimensions.
On measure solutions of the Boltzmann equation, part I: Moment production and stability estimates
Lu, Xuguang; Mouhot, Clément
The spatially homogeneous Boltzmann equation with hard potentials is considered for measure valued initial data having finite mass and energy. We prove the existence of weak measure solutions, with and without angular cutoff on the collision kernel; the proof in particular makes use of an approximation argument based on the Mehler transform. Moment production estimates in the usual form and in the exponential form are obtained for these solutions. Finally for the Grad angular cutoff, we also establish uniqueness and strong stability estimate on these solutions.
Blow-up estimates for semilinear parabolic systems coupled in an equation and a boundary condition
Institute of Scientific and Technical Information of China (English)
WANG; Mingxin(
2001-01-01
［1］Wang, S., Wang, M. X., Xie, C. H., Reaction-diffusion systems with nonlinear boundary conditions, Z. angew. Math.Phys., 1997, 48(6): 994－1001.［2］Fila, M., Quittner, P., The blow-up rate for a semilinear parabolic system, J. Math. Anal. Appl., 1999, 238: 468－476.［3］Hu, B., Remarks on the blow-up estimate for solutions of the heat equation with a nonlinear boundary condition, Differential Integral Equations, 1996, 9(5): 891－901.［4］Hu, B. , Yin, H. M., The profile near blow-up time for solution of the heat equation with a nonlinear boundary condition,Trans. of Amer. Math. Soc., 1994, 346: 117－135.［5］Amann, H., Parabolic equations and nonlinear boundary conditions, J. of Diff. Eqns., 1988, 72: 201－269.［6］Deng, K., Blow-up rates for parabolic systems, Z. angew. Math. Phys. ,1996, 47: 132－143.［7］Fila, M., Levine, H. A., On critical exponents for a semilinear parabolic system coupled in an equation and a boundary condition, J. Math. Anal. Appl., 1996, 204: 494－521.
Callias, Céline; Ezri, Jessica; Marques-Vidal, Pedro Manuel; Nydegger, Andreas
2016-05-01
To assess the agreement of commonly used skinfold thickness equations to estimate percentage of Fat Mass (FM%) in paediatric patients with IBD, in comparison with dual energy X-ray absorptiometry (DEXA). Twenty-one paediatric IBD patients were included: 11 females and 10 males; mean age for the entire group: 14.3 years, range 12-16 years, 16 with Crohn's disease, five with ulcerative colitis. The FM% was calculated using six established paediatric skinfold thickness equations and compared to the results obtained by DEXA. The statistical analysis was performed using Spearman's correlation, Lin's concordance correlation coefficient and corresponding 95% confidence interval, Bland-Altman's limits of agreement method and the Bradley-Blackwood test. Correlation between skinfold and DEXA values ranged between 0.85 (Deurenberg) and 0.92 (Durnin and Rahaman and Johnston), all P skinfold and DEXA values ranged between -3.6% (Deurenberg) and 2.5% (Weststrate). Bland-Altman limits of agreement were wide, spanning over 10%. Finally, the Bradley-Blackwood test of equality of means and variances was significant in all but the Durnin and Rahaman equation. In adolescents with IBD, fat mass calculated from six skinfold thickness equations showed good correlation but poor agreement with reference values from DEXA. Assessment of body composition using skinfold thickness equations cannot be recommended in paediatric patients with IBD. © 2016 Paediatrics and Child Health Division (The Royal Australasian College of Physicians).
Mehdizadeh, Saeid; Behmanesh, Javad; Khalili, Keivan
2016-08-01
In the present research, three artificial intelligence methods including Gene Expression Programming (GEP), Artificial Neural Networks (ANN) and Adaptive Neuro-Fuzzy Inference System (ANFIS) as well as, 48 empirical equations (10, 12 and 26 equations were temperature-based, sunshine-based and meteorological parameters-based, respectively) were used to estimate daily solar radiation in Kerman, Iran in the period of 1992-2009. To develop the GEP, ANN and ANFIS models, depending on the used empirical equations, various combinations of minimum air temperature, maximum air temperature, mean air temperature, extraterrestrial radiation, actual sunshine duration, maximum possible sunshine duration, sunshine duration ratio, relative humidity and precipitation were considered as inputs in the mentioned intelligent methods. To compare the accuracy of empirical equations and intelligent models, root mean square error (RMSE), mean absolute error (MAE), mean absolute relative error (MARE) and determination coefficient (R2) indices were used. The results showed that in general, sunshine-based and meteorological parameters-based scenarios in ANN and ANFIS models presented high accuracy than mentioned empirical equations. Moreover, the most accurate method in the studied region was ANN11 scenario with five inputs. The values of RMSE, MAE, MARE and R2 indices for the mentioned model were 1.850 MJ m-2 day-1, 1.184 MJ m-2 day-1, 9.58% and 0.935, respectively.
Neuenkirch, Andreas
2011-01-01
We study a least square-type estimator for an unknown parameter in the drift coefficient of a stochastic differential equation with additive fractional noise of Hurst parameter H>1/2. The estimator is based on discrete time observations of the stochastic differential equation, and using tools from ergodic theory and stochastic analysis we derive its strong consistency.
John Yarie; Bert R. Mead
1988-01-01
Equations are presented for estimating the twig, foliage, and combined biomass for 58 plant species in interior Alaska. The equations can be used for estimating biomass from percentage of foliar cover of 10-centimeter layers in a vertical profile from 0 to 6 meters. Few differences were found in regressions of the same species between layers except when the ratio of...
Asiri, Sharefa M.
2017-10-08
Partial Differential Equations (PDEs) are commonly used to model complex systems that arise for example in biology, engineering, chemistry, and elsewhere. The parameters (or coefficients) and the source of PDE models are often unknown and are estimated from available measurements. Despite its importance, solving the estimation problem is mathematically and numerically challenging and especially when the measurements are corrupted by noise, which is often the case. Various methods have been proposed to solve estimation problems in PDEs which can be classified into optimization methods and recursive methods. The optimization methods are usually heavy computationally, especially when the number of unknowns is large. In addition, they are sensitive to the initial guess and stop condition, and they suffer from the lack of robustness to noise. Recursive methods, such as observer-based approaches, are limited by their dependence on some structural properties such as observability and identifiability which might be lost when approximating the PDE numerically. Moreover, most of these methods provide asymptotic estimates which might not be useful for control applications for example. An alternative non-asymptotic approach with less computational burden has been proposed in engineering fields based on the so-called modulating functions. In this dissertation, we propose to mathematically and numerically analyze the modulating functions based approaches. We also propose to extend these approaches to different situations. The contributions of this thesis are as follows. (i) Provide a mathematical analysis of the modulating function-based method (MFBM) which includes: its well-posedness, statistical properties, and estimation errors. (ii) Provide a numerical analysis of the MFBM through some estimation problems, and study the sensitivity of the method to the modulating functions\\' parameters. (iii) Propose an effective algorithm for selecting the method\\'s design parameters
Institute of Scientific and Technical Information of China (English)
Gao Lingyun
2012-01-01
We apply Nevanlinna theory of the value distribution of meromorphic functions to study the properties of Nevanlinna counting function and proximity function of meromorphic solutions of a type of systems of complex difference equations.Our results can give estimates on the proximity function and the counting function of solutions of systems of difference equations.This implies that solutions have a relatively large number of poles.It extend some result concerning difference equations to the systems of difference equations.
Directory of Open Access Journals (Sweden)
Satoshi Suzuki
2013-01-01
Full Text Available For an establishment of a skill evaluation method for human support systems, development of an estimating equation of the machine operational skill is presented. Factors of the eye movement such as frequency, velocity, and moving distance of saccade were computed using the developed eye gaze measurement system, and the eye movement features were determined from these factors. The estimating equation was derived through an outlier test (to eliminate nonstandard data and a principal component analysis (to find dominant components. Using a cooperative carrying task (cc-task simulator, the eye movement and operational data of the machine operators were recorded, and effectiveness of the derived estimating equation was investigated. As a result, it was confirmed that the estimating equation was effective strongly against actual simple skill levels (r=0.56–0.84. In addition, effects of internal condition such as fatigue and stress on the estimating equation were analyzed. Using heart rate (HR and coefficient of variation of R-R interval (Cvrri. Correlation analysis between these biosignal indexes and the estimating equation of operational skill found that the equation reflected effects of stress and fatigue, although the equation could estimate the skill level adequately.
Equation reliability of soil ingestion estimates in mass-balance soil ingestion studies.
Stanek Iii, Edward J; Xu, Bo; Calabrese, Edward J
2012-03-01
Exposure to chemicals from ingestion of contaminated soil may be an important pathway with potential health consequences for children. A key parameter used in assessing this exposure is the quantity of soil ingested, with estimates based on four short longitudinal mass-balance soil ingestion studies among children. The estimates use trace elements in the soil with low bioavailability that are minimally present in food. Soil ingestion corresponds to the excess trace element amounts excreted, after subtracting trace element amounts ingested from food and medications, expressed as an equivalent quantity of soil. The short duration of mass-balance studies, different concentrations of trace elements in food and soil, and potential for trace elements to be ingested from other nonsoil, nonfood sources contribute to variability and bias in the estimates. We develop a stochastic model for a soil ingestion estimator based on a trace element that accounts for critical features of the mass-balance equation. Using results from four mass-balance soil ingestion studies, we estimate the accuracy of soil ingestion estimators for different trace elements, and identify subjects where the difference between Al and Si estimates is larger (>3 RMSE) than expected. Such large differences occur in fewer than 12% of subjects in each of the four studies. We recommend the use of such criteria to flag and exclude subjects from soil ingestion analyses. © 2011 Society for Risk Analysis.
Equations for estimating bankfull channel geometry and discharge for streams in Massachusetts
Bent, Gardner C.; Waite, Andrew M.
2013-01-01
Regression equations were developed for estimating bankfull geometry—width, mean depth, cross-sectional area—and discharge for streams in Massachusetts. The equations provide water-resource and conservation managers with methods for estimating bankfull characteristics at specific stream sites in Massachusetts. This information can be used for the adminstration of the Commonwealth of Massachusetts Rivers Protection Act of 1996, which establishes a protected riverfront area extending from the mean annual high-water line corresponding to the elevation of bankfull discharge along each side of a perennial stream. Additionally, information on bankfull channel geometry and discharge are important to Federal, State, and local government agencies and private organizations involved in stream assessment and restoration projects. Regression equations are based on data from stream surveys at 33 sites (32 streamgages and 1 crest-stage gage operated by the U.S. Geological Survey) in and near Massachusetts. Drainage areas of the 33 sites ranged from 0.60 to 329 square miles (mi2). At 27 of the 33 sites, field data were collected and analyses were done to determine bankfull channel geometry and discharge as part of the present study. For 6 of the 33 sites, data on bankfull channel geometry and discharge were compiled from other studies done by the U.S. Geological Survey, Natural Resources Conservation Service of the U.S. Department of Agriculture, and the Vermont Department of Environmental Conservation. Similar techniques were used for field data collection and analysis for bankfull channel geometry and discharge at all 33 sites. Recurrence intervals of the bankfull discharge, which represent the frequency with which a stream fills its channel, averaged 1.53 years (median value 1.34 years) at the 33 sites. Simple regression equations were developed for bankfull width, mean depth, cross-sectional area, and discharge using drainage area, which is the most significant explanatory
Time-Delay Estimation using the Characteristic Roots of Delay Differential Equations
Directory of Open Access Journals (Sweden)
Sun Yi
2012-01-01
Full Text Available Problem statement: For ordinary dynamic systems (i.e., non-delayed, various methods such as linear least-squares, gradient-weighted least-squares, Kalman filtering and other robust techniques have been widely used in signal processing, robotics, civil engineering. On the other hand, time-delay estimation of systems with unknown time-delay is still a challenging problem due to difficulty in formulation caused. Approach: The presented method makes use of the Lambert W function and analytical solutions of scalar first-order Delay Differential Equations (DDEs. The Lambert W function has been known to be useful in solving delay differential equations. From the solutions in terms of the Lambert W function, the dominant characteristic roots can be obtained and used to estimate time-delays. The function is already embedded in various software packages (e.g., MATLAB and thus, the presented method can be readily used for time-delay systems. Results: The presented method and the provided examples show ease of formulation and accuracy of time-delay estimation. Conclusion: Estimation of time-delays can be conducted in an analytical way. The presented method will be extended to general systems of DDEs and application to physical systems.
Estimation of Bid Curves in Power Exchanges using Time-varying Simultaneous-Equations Models
Ofuji, Kenta; Yamaguchi, Nobuyuki
Simultaneous-equations model (SEM) is generally used in economics to estimate interdependent endogenous variables such as price and quantity in a competitive, equilibrium market. In this paper, we have attempted to apply SEM to JEPX (Japan Electric Power eXchange) spot market, a single-price auction market, using the publicly available data of selling and buying bid volumes, system price and traded quantity. The aim of this analysis is to understand the magnitude of influences to the auctioned prices and quantity from the selling and buying bids, than to forecast prices and quantity for risk management purposes. In comparison with the Ordinary Least Squares (OLS) estimation where the estimation results represent average values that are independent of time, we employ a time-varying simultaneous-equations model (TV-SEM) to capture structural changes inherent in those influences, using State Space models with Kalman filter stepwise estimation. The results showed that the buying bid volumes has that highest magnitude of influences among the factors considered, exhibiting time-dependent changes, ranging as broad as about 240% of its average. The slope of the supply curve also varies across time, implying the elastic property of the supply commodity, while the demand curve remains comparatively inelastic and stable over time.
Directory of Open Access Journals (Sweden)
Kovačić Nataša
2015-11-01
Full Text Available The paper addresses the effect of external integration (EI with transport suppliers on the efficiency of travel agencies in the tourism sector supply chains. The main aim is the comparison of different estimation methods used in the structural equation modeling (SEM, applied to discover possible relationships between EIs and efficiencies. The latter are calculated by the means of data envelopment analysis (DEA. While designing the structural equation model, the exploratory and confirmatory factor analyses are also used as preliminary statistical procedures. For the estimation of parameters of SEM model, three different methods are explained, analyzed and compared: maximum likelihood (ML method, Bayesian Markov Chain Monte Carlo (BMCMC method, and unweighted least squares (ULS method. The study reveals that all estimation methods calculate comparable estimated parameters. The results also give an evidence of good model fit performance. Besides, the research confirms that the amplified external integration with transport providers leads to increased efficiency of travel agencies, which might be a very interesting finding for the operational management.
Magnitude Estimation for the 2011 Tohoku-Oki Earthquake Based on Ground Motion Prediction Equations
Eshaghi, Attieh; Tiampo, Kristy F.; Ghofrani, Hadi; Atkinson, Gail M.
2015-08-01
This study investigates whether real-time strong ground motion data from seismic stations could have been used to provide an accurate estimate of the magnitude of the 2011 Tohoku-Oki earthquake in Japan. Ultimately, such an estimate could be used as input data for a tsunami forecast and would lead to more robust earthquake and tsunami early warning. We collected the strong motion accelerograms recorded by borehole and free-field (surface) Kiban Kyoshin network stations that registered this mega-thrust earthquake in order to perform an off-line test to estimate the magnitude based on ground motion prediction equations (GMPEs). GMPEs for peak ground acceleration and peak ground velocity (PGV) from a previous study by Eshaghi et al. in the Bulletin of the Seismological Society of America 103. (2013) derived using events with moment magnitude ( M) ≥ 5.0, 1998-2010, were used to estimate the magnitude of this event. We developed new GMPEs using a more complete database (1998-2011), which added only 1 year but approximately twice as much data to the initial catalog (including important large events), to improve the determination of attenuation parameters and magnitude scaling. These new GMPEs were used to estimate the magnitude of the Tohoku-Oki event. The estimates obtained were compared with real time magnitude estimates provided by the existing earthquake early warning system in Japan. Unlike the current operational magnitude estimation methods, our method did not saturate and can provide robust estimates of moment magnitude within ~100 s after earthquake onset for both catalogs. It was found that correcting for average shear-wave velocity in the uppermost 30 m () improved the accuracy of magnitude estimates from surface recordings, particularly for magnitude estimates of PGV (Mpgv). The new GMPEs also were used to estimate the magnitude of all earthquakes in the new catalog with at least 20 records. Results show that the magnitude estimate from PGV values using
Estimating order-picking times for return heuristic - equations and simulations
Directory of Open Access Journals (Sweden)
Grzegorz Tarczyński
2015-09-01
Full Text Available Background: A key element of the evaluation of warehouse operation is the average order-picking time. In warehouses where the order-picking process is carried out according to the "picker-to-part" rule the order-picking time is usually proportional to the distance covered by the picker while picking items. This distance can by estimated by simulations or using mathematical equations. In the paper only the best described in the literature one-block rectangular warehouses are considered. Material and methods: For the one-block rectangular warehouses there are well known five routing heuristics. In the paper the author considers the return heuristic in two variants. The paper presents well known Hall's and De Koster's equations for the average distance traveled by the picker while completing items from one pick list. The author presents own proposals for calculating the expected distance. Results: the results calculated by the use of mathematical equations (the formulas of Hall, De Koster and own propositions were compared with the average values obtained using computer simulations. For the most cases the average error does not exceed 1% (except for Hall's equations. To carry out simulation the computer software Warehouse Real-Time Simulator was used. Conclusions: the order-picking time is a function of many variables and its optimization is not easy. It can be done in two stages: firstly using mathematical equations the set of the potentially best variants is established, next the results are verified using simulations. The results calculated by the use of equations are not precise, but possible to achieve immediately. The simulations are more time-consuming, but allow to analyze the order-picking process more accurately.
Erdoğan, M. Burak; Green, William R.
2017-06-01
We investigate dispersive estimates for the two dimensional Dirac equation with a potential. In particular, we show that the Dirac evolution satisfies a t -1 decay rate as an operator from the Hardy space H 1 to BMO, the space of functions of bounded mean oscillation. This estimate, along with the L 2 conservation law allows one to deduce a family of Strichartz estimates. We classify the structure of threshold obstructions as being composed of s-wave resonances, p-wave resonances and eigenfunctions. We show that, as in the case of the Schrödinger evolution, the presence of a threshold s-wave resonance does not destroy the t -1 decay rate. As a consequence of our analysis we obtain a limiting absorption principle in the neighborhood of the threshold, and show that there are only finitely many eigenvalues in the spectral gap.
Sharp asymptotic estimates for vorticity solutions of the 2D Navier-Stokes equation
Directory of Open Access Journals (Sweden)
Yuncheng You
2008-12-01
Full Text Available The asymptotic dynamics of high-order temporal-spatial derivatives of the two-dimensional vorticity and velocity of an incompressible, viscous fluid flow in $mathbb{R}^2$ are studied, which is equivalent to the 2D Navier-Stokes equation. It is known that for any integrable initial vorticity, the 2D vorticity solution converges to the Oseen vortex. In this paper, sharp exterior decay estimates of the temporal-spatial derivatives of the vorticity solution are established. These estimates are then used and combined with similarity and $L^p$ compactness to show the asymptotical attraction rates of temporal-spatial derivatives of generic 2D vorticity and velocity solutions by the Oseen vortices and velocity solutions respectively. The asymptotic estimates and the asymptotic attraction rates of all the derivatives obtained in this paper are independent of low or high Reynolds numbers.
Babaniyi, Olalekan A; Barbone, Paul E
2015-01-01
We consider the problem of estimating the $2D$ vector displacement field in a heterogeneous elastic solid deforming under plane stress conditions. The problem is motivated by applications in quasistatic elastography. From precise and accurate measurements of one component of the $2D$ vector displacement field and very limited information of the second component, the method reconstructs the second component quite accurately. No a priori knowledge of the heterogeneous distribution of material properties is required. This method relies on using a special form of the momentum equations to filter ultrasound displacement measurements to produce more precise estimates. We verify the method with applications to simulated displacement data. We validate the method with applications to displacement data measured from a tissue mimicking phantom, and in-vivo data; significant improvements are noticed in the filtered displacements recovered from all the tests. In verification studies, error in lateral displacement estimate...
Development of regional parameter estimation equations for a macroscale hydrologic model
Abdulla, Fayez A.; Lettenmaier, Dennis P.
1997-10-01
A methodology for developing regional parameter estimation equations, designed for application to continental scale river basins, is described. The approach, which is applied to the two-layer Variable Infiltration Capacity (VIC-2L) land surface hydrologic model, uses a set of 34 unregulated calibration or "training" catchments (drainage areas 10 2-10 4 km 2) distributed throughout the Arkansas-Red River basin of the south central U.S. For each of these catchments, parameters were determined by: a) prior estimation of two of the model parameters (saturated hydraulic conductivity and pore size distribution index) from the U.S. Soil Conservation Service State Soil Geographic Data Base (STATSGO) data base; and b) estimation of the remaining seven parameters via a search procedure that minimizes the sum of squares of differences between predicted and observed streamflow. The catchment parameters were then related to 11 ancillary distributed land surface characteristics extracted from STATSGO, and 17 variables derived from station meteorological data. The seven regression equations explained from 54 to 76% of the variance of the parameters. The most frequently occurring ancillary variables were the average permeability, saturated hydraulic conductivity, and SCS hydrologic Group B (typically soils with moderately high infiltration rates) fraction derived from STATSGO, and the average temperature and standard deviation of fall precipitation. The method was tested by comparing simulations using the regional (regression equation) parameters for six unregulated catchments not in the parameter estimation set. The model performance using the regional parameters was quite good for most of the calibration and validation catchments, which were humid and semi-humid. The model did not perform as well for the smaller number of arid to semi-arid catchments.
PINTO, Andressa S.; CHEDID, Marcio F.; GUERRA, Léa T.; ÁLVARES-DA-SILVA, Mario R.; de ARAÚJO, Alexandre; GUIMARÃES, Luciano S.; LEIPNITZ, Ian; CHEDID, Aljamir D.; KRUEL, Cleber R. P.; GREZZANA-FILHO, Tomaz J. M.; KRUEL, Cleber D. P.
2016-01-01
ABSTRACT Background: Reliable measurement of basal energy expenditure (BEE) in liver transplant (LT) recipients is necessary for adapting energy requirements, improving nutritional status and preventing weight gain. Indirect calorimetry (IC) is the gold standard for measuring BEE. However, BEE may be estimated through alternative methods, including electrical bioimpedance (BI), Harris-Benedict Equation (HBE), and Mifflin-St. Jeor Equation (MSJ) that carry easier applicability and lower cost. Aim: To determine which of the three alternative methods for BEE estimation (HBE, BI and MSJ) would provide most reliable BEE estimation in LT recipients. Methods: Prospective cross-sectional study including dyslipidemic LT recipients in follow-up at a 735-bed tertiary referral university hospital. Comparisons of BEE measured through IC to BEE estimated through each of the three alternative methods (HBE, BI and MSJ) were performed using Bland-Altman method and Wilcoxon Rank Sum test. Results: Forty-five patients were included, aged 58±10 years. BEE measured using IC was 1664±319 kcal for males, and 1409±221 kcal for females. Average difference between BEE measured by IC (1534±300 kcal) and BI (1584±377 kcal) was +50 kcal (p=0.0384). Average difference between the BEE measured using IC (1534±300 kcal) and MSJ (1479.6±375 kcal) was -55 kcal (p=0.16). Average difference between BEE values measured by IC (1534±300 kcal) and HBE (1521±283 kcal) was -13 kcal (p=0.326). Difference between BEE estimated through IC and HBE was less than 100 kcal for 39 of all 43patients. Conclusions: Among the three alternative methods, HBE was the most reliable for estimating BEE in LT recipients. PMID:27759783
Dijk, P.R. van; Kramer, A.; Logtenberg, S.J.; Hoitsma, A.J.; Kleefstra, N.; Jager, K.J.; Bilo, H.J.G.
2015-01-01
OBJECTIVES: Describe the incidence, prevalence and survival of patients needing renal replacement therapy (RRT) for end-stage renal disease (ESRD) due to diabetes mellitus (DM)-related glomerulosclerosis or nephropathy (diabetic nephropathy, DN) in the Netherlands. DESIGN: Using the national registr
van Dijk, Peter R.; Kramer, Anneke; Logtenberg, Susan J. J.; Hoitsma, Andries J.; Kleefstra, Nanne; Jager, Kitty J.; Bilo, Henk J. G.
2015-01-01
Objectives: Describe the incidence, prevalence and survival of patients needing renal replacement therapy (RRT) for end-stage renal disease (ESRD) due to diabetes mellitus (DM)-related glomerulosclerosis or nephropathy (diabetic nephropathy, DN) in the Netherlands. Design: Using the national registr
Dijk, P.R. van; Kramer, A.; Logtenberg, S.J.; Hoitsma, A.J.; Kleefstra, N.; Jager, K.J.; Bilo, H.J.G.
2015-01-01
OBJECTIVES: Describe the incidence, prevalence and survival of patients needing renal replacement therapy (RRT) for end-stage renal disease (ESRD) due to diabetes mellitus (DM)-related glomerulosclerosis or nephropathy (diabetic nephropathy, DN) in the Netherlands. DESIGN: Using the national
Estimation of health effects of prenatal methylmercury exposure using structural equation models
DEFF Research Database (Denmark)
Budtz-Jørgensen, Esben; Keiding, Niels; Grandjean, Philippe
2002-01-01
BACKGROUND: Observational studies in epidemiology always involve concerns regarding validity, especially measurement error, confounding, missing data, and other problems that may affect the study outcomes. Widely used standard statistical techniques, such as multiple regression analysis, may...... to some extent adjust for these shortcomings. However, structural equations may incorporate most of these considerations, thereby providing overall adjusted estimations of associations. This approach was used in a large epidemiological data set from a prospective study of developmental methyl......-mercury toxicity. RESULTS: Structural equation models were developed for assessment of the association between biomarkers of prenatal mercury exposure and neuropsychological test scores in 7 year old children. Eleven neurobehavioral outcomes were grouped into motor function and verbally mediated function...
Bevc, Sebastjan; Hojs, Nina; Hojs, Radovan; Ekart, Robert; Gorenjak, Maksimiljan; Puklavec, Ludvik
2017-04-01
Estimating glomerular filtration rate (GFR) in elderly patients is a problem, since they are poorly represented in studies developing GFR equations. Serum cystatin C is a better indicator of GFR than serum creatinine in elderly patients. Therefore the aim of our study was to compare frequently used serum cystatin C based GFR equations with a gold standard ((51) CrEDTA clearance) in elderly chronic kidney disease (CKD) patients. 106 adult Caucasian patients, older than 65 years (58 women, 48 men; mean age 72.5 years), were included. In each patient (51) CrEDTA clearance, serum creatinine (IDMS traceable method) and serum cystatin C (immunonephelometric method) were determined. GFR was estimated using the Simple cystatin C, CKD-EPI cystatin C, CKD-EPI creatinine-cystatin C and BIS2 equation. Mean serum creatinine of our patients was 141.4 ± 41.5 μmol/L, mean serum cystatin C 1.79 ± 0.6 mg/L, mean (51) CrEDTA clearance was 52.2 ± 15.9 mL/min per 1.73 m(2) . Statistically significant correlations between (51) CrEDTA clearance and all formulas were found (P C and BIS2 equation underestimated and CKD-EPI cystatin C and Simple cystatin C equation overestimated measured GFR. All equations lacked precision. Analysis of ability to correctly predict patient's GFR below or above 45 mL/min per 1.73 m(2) showed similar ability for all equations (P = 0.24-0.89). All equations are equally accurate for estimating GFR in elderly Caucasian CKD patients. For daily practice Simple cystatin C equation is most practical.
Indirect estimation of VO2max in athletes by ACSM’s equation: valid or not?
Koutlianos, N; Dimitros, E; Metaxas, T; Cansiz, M; Deligiannis, AS; Kouidi, E
2013-01-01
Aim: The purpose of this study was to assess the indirect calculation of VO2max using ACSM’s equation for Bruce protocol in athletes of different sports and to compare with the directly measured; secondly to develop regression models predicting VO2 max in athletes. Methods: Fifty five male athletes of national and international level (mean age 28.3 ± 5.6 yrs) performed graded exercise test with direct measurement of VO2 through ergospirometric device. Moreover, 3 equations were used for the indirect calculation of VO2max: a) VO2max= (0.2 · Speed) + (0.9 · Speed · Grade) + 3.5 (ACSM running equation), b) regression analysis model using enter method and c) stepwise method based on the measured data of VO2. Age, BMI, speed, grade and exercise time were used as independent variables. Results: Regression analysis using enter method yielded the equation (R=.64, standard error of estimation [SEE] = 6.11): VO2max (ml·kg-1·min-1) = 58.443 - (0.215 · age) - (0.632 · BMI) - (68.639 · grade) + (1.579 · time) while stepwise method (R = .61, SEE = 6.18) led to: VO2max (ml·kg-1·min-1) = 33.971 - (0.291 · age) + (1.481 · time). The calculated values of VO2max from these regression models did not differ significantly from the measured VO2max (p>.05). On the contrary, VO2max calculated from the ACSM’s running equation was significantly higher from the actually measured value by 14.6% (p VO2max in athletes aged 18-37 years using Bruce protocol. Only the regression models were correlated moderately with the actually measured values of VO2max. PMID:24376318
Indirect estimation of VO2max in athletes by ACSM's equation: valid or not?
Koutlianos, N; Dimitros, E; Metaxas, T; Cansiz, M; Deligiannis, As; Kouidi, E
2013-04-01
The purpose of this study was to assess the indirect calculation of VO2max using ACSM's equation for Bruce protocol in athletes of different sports and to compare with the directly measured; secondly to develop regression models predicting VO2 max in athletes. Fifty five male athletes of national and international level (mean age 28.3 ± 5.6 yrs) performed graded exercise test with direct measurement of VO2 through ergospirometric device. Moreover, 3 equations were used for the indirect calculation of VO2max: a) VO2max= (0.2 · Speed) + (0.9 · Speed · Grade) + 3.5 (ACSM running equation), b) regression analysis model using enter method and c) stepwise method based on the measured data of VO2. Age, BMI, speed, grade and exercise time were used as independent variables. Regression analysis using enter method yielded the equation (R=.64, standard error of estimation [SEE] = 6.11): VO2max (ml·kg(-1)·min(-1)) = 58.443 - (0.215 · age) - (0.632 · BMI) - (68.639 · grade) + (1.579 · time) while stepwise method (R = .61, SEE = 6.18) led to: VO2max (ml·kg(-1)·min(-1)) = 33.971 - (0.291 · age) + (1.481 · time). The calculated values of VO2max from these regression models did not differ significantly from the measured VO2max (p>.05). On the contrary, VO2max calculated from the ACSM's running equation was significantly higher from the actually measured value by 14.6% (p VO2max in athletes aged 18-37 years using Bruce protocol. Only the regression models were correlated moderately with the actually measured values of VO2max.
A superlinear convergence estimate for an iterative method for the biharmonic equation
Energy Technology Data Exchange (ETDEWEB)
Horn, M.A. [Wichita State Univ., Wichita, KS (United States)
1996-12-31
In [CDH] a method for the solution of boundary value problems for the biharmonic equation using conformal mapping was investigated. The method is an implementation of the classical method of Muskhelishvili. In [CDH] it was shown, using the Hankel structure, that the linear system in [Musk] is the discretization of the identify plus a compact operator, and therefore the conjugate gradient method will converge superlinearly. The purpose of this paper is to give an estimate of the superlinear convergence in the case when the boundary curve is in a Hoelder class.
Institute of Scientific and Technical Information of China (English)
Yan-ping Chen; Yun-qing Huang
2001-01-01
Improved L2-error estimates are computed for mixed finite element methods for second order nonlinear hyperbolic equations. Results are given for the continuous-time case. The convergence of the values for both the scalar function and the flux is demonstrated. The technique used here covers the lowest-order Raviart-Thomas spaces, as well as the higherorder spaces. A second paper will present the analysis of a fully discrete scheme (Numer.Math. J. Chinese Univ. vol.9, no.2, 2000, 181-192).
Dispersion estimates for one-dimensional Schrödinger and Klein-Gordon equations revisited
Egorova, I. E.; Kopylova, E. A.; Marchenko, V. A.; Teschl, G.
2016-06-01
It is shown that for a one-dimensional Schrödinger operator with a potential whose first moment is integrable the elements of the scattering matrix are in the unital Wiener algebra of functions with integrable Fourier transforms. This is then used to derive dispersion estimates for solutions of the associated Schrödinger and Klein-Gordon equations. In particular, the additional decay conditions are removed in the case where a resonance is present at the edge of the continuous spectrum. Bibliography: 29 titles.
Chronic renal failure among HIV-1-infected patients
DEFF Research Database (Denmark)
Mocroft, Amanda; Kirk, Ole; Gatell, Jose
2007-01-01
BACKGROUND: The role of exposure to antiretrovirals in chronic renal failure (CRF) is not well understood. Glomerular filtration rates (GFR) are estimated using the Cockcroft-Gault (CG) or Modification of Diet in Renal Disease (MDRD) equations. METHODS: Baseline was arbitrarily defined as the first...
Chronic renal failure among HIV-1-infected patients
DEFF Research Database (Denmark)
Mocroft, Amanda; Kirk, Ole; Gatell, Jose
2007-01-01
BACKGROUND: The role of exposure to antiretrovirals in chronic renal failure (CRF) is not well understood. Glomerular filtration rates (GFR) are estimated using the Cockcroft-Gault (CG) or Modification of Diet in Renal Disease (MDRD) equations. METHODS: Baseline was arbitrarily defined as the first...
Cao, Jiguo
2012-01-01
Ordinary differential equations (ODEs) are widely used in biomedical research and other scientific areas to model complex dynamic systems. It is an important statistical problem to estimate parameters in ODEs from noisy observations. In this article we propose a method for estimating the time-varying coefficients in an ODE. Our method is a variation of the nonlinear least squares where penalized splines are used to model the functional parameters and the ODE solutions are approximated also using splines. We resort to the implicit function theorem to deal with the nonlinear least squares objective function that is only defined implicitly. The proposed penalized nonlinear least squares method is applied to estimate a HIV dynamic model from a real dataset. Monte Carlo simulations show that the new method can provide much more accurate estimates of functional parameters than the existing two-step local polynomial method which relies on estimation of the derivatives of the state function. Supplemental materials for the article are available online.
Cao, Jiguo; Huang, Jianhua Z; Wu, Hulin
2012-01-01
Ordinary differential equations (ODEs) are widely used in biomedical research and other scientific areas to model complex dynamic systems. It is an important statistical problem to estimate parameters in ODEs from noisy observations. In this article we propose a method for estimating the time-varying coefficients in an ODE. Our method is a variation of the nonlinear least squares where penalized splines are used to model the functional parameters and the ODE solutions are approximated also using splines. We resort to the implicit function theorem to deal with the nonlinear least squares objective function that is only defined implicitly. The proposed penalized nonlinear least squares method is applied to estimate a HIV dynamic model from a real dataset. Monte Carlo simulations show that the new method can provide much more accurate estimates of functional parameters than the existing two-step local polynomial method which relies on estimation of the derivatives of the state function. Supplemental materials for the article are available online.
Pankovic, V; Glavatovic, R
2009-01-01
In this work we consider the Peter principle and anti-Peter principle as the discrete logistic and discrete inverse logistic equation. Especially we discuss imprecisely estimated (by hierarchical control mechanism) carrying capacity, i.e. boundary (in)competence level of a hierarchy member. It implies that Peter principle holds two sub-principles. In the first one objective boundary competence level is increased for estimation error. In the second one objective boundary competence level is decreased for estimation error. Similarly, anti-Peter principle holds two sub-principles too. All this implies that paradoxical situations that follow from Peter and anti-Peter principle can be simply removed by decrease of the error of hierarchical (social) control. Also we discuss cases by Peter principle when error of the boundary competence level by estimation grows up. (Then, in fact, there is no estimation error but stimulation of the boundary level by control mechanism.) By first Peter sub-principle it implies anarch...
An analysis of a new nonlinear estimation technique: The state-dependent Ricatti equation method
Ewing, Craig Michael
1999-10-01
Research into nonlinear estimation techniques for terminal homing missiles has been conducted for many decades. The terminal state estimator, also called the guidance filter, is responsible for providing accurate estimates of target motion for use in guiding the missile to a collision course with the target. Some form of the extended-Kalman filter (EKF) has become the standard estimation technique employed in most modern weapon guidance systems. EKF linearization of nonlinear dynamics and/or measurements can cause problems of divergence when confronted by highly nonlinear conditions. The objective of this dissertation is to analyze a new nonlinear estimation technique that is based on the parameterization of the nonlinearities. This parameterization converts the nonlinear estimation problem into the form of a steady-state continuous Kalman filtering problem with state-dependent coefficients. This new technique, called the state-dependent Ricatti equation filter (SDREF), allows the nonlinearities of the system to be fully incorporated into the filter design, before stochastic uncertainties are imposed, without the need for linearization. The SDREF was investigated in three problems: an exoatmospheric, terminal homing, ballistic-missile intercept problem; a highly nonlinear pendulum example; and an algorithmic loss of observability problem. The exoatmospheric guidance problem examined nonlinear measurements with linear dynamics. To investigate the SDREF when used with a combination of nonlinear dynamics and nonlinear measurements, a highly nonlinear, two-state pendulum problem was also examined. While these problems were useful in gaining insight into the performance characteristics of the SDREF, no formal proof of stability could be determined for the original formulation of the estimator. The original SDREF solved an algebraic SDRE that arose from an infinite-time horizon formulation of the nonlinear filtering problem. A modification to the SDREF formulation was
Probabilistic formulation of estimation problems for a class of Hamilton-Jacobi equations
Hofleitner, Aude
2012-12-01
This article presents a method for deriving the probability distribution of the solution to a Hamilton-Jacobi partial differential equation for which the value conditions are random. The derivations lead to analytical or semi-analytical expressions of the probability distribution function at any point in the domain in which the solution is defined. The characterization of the distribution of the solution at any point is a first step towards the estimation of the parameters defining the random value conditions. This work has important applications for estimation in flow networks in which value conditions are noisy. In particular, we illustrate our derivations on a road segment with random capacity reductions. © 2012 IEEE.
Error Estimates for a Semidiscrete Finite Element Method for Fractional Order Parabolic Equations
Jin, Bangti
2013-01-01
We consider the initial boundary value problem for a homogeneous time-fractional diffusion equation with an initial condition ν(x) and a homogeneous Dirichlet boundary condition in a bounded convex polygonal domain Ω. We study two semidiscrete approximation schemes, i.e., the Galerkin finite element method (FEM) and lumped mass Galerkin FEM, using piecewise linear functions. We establish almost optimal with respect to the data regularity error estimates, including the cases of smooth and nonsmooth initial data, i.e., ν ∈ H2(Ω) ∩ H0 1(Ω) and ν ∈ L2(Ω). For the lumped mass method, the optimal L2-norm error estimate is valid only under an additional assumption on the mesh, which in two dimensions is known to be satisfied for symmetric meshes. Finally, we present some numerical results that give insight into the reliability of the theoretical study. © 2013 Society for Industrial and Applied Mathematics.
Haddadin, Raja; Qian, Feng; Desikan, Sridhar; Hussain, Munir; Smith, Ronald L
2009-01-01
The solubility of drugs in polyethylene glycol 400 (PEG 400) was estimated and rank ordered using a differential scanning calorimetry (DSC) method and the Fox Equation. Drug-polymer binary mixtures of six compounds (Ibuprofen, Indomethacin, Naproxen, and three proprietary compounds: PC-1 through PC-3) with PEG 400 were heat treated using a three-cycle DSC method to establish a correlation between equilibrium solubility and temperature. Thermal events such as heat of fusion, heat of recrystallization and glass transition temperature, T(g), were used to calculate the drug solubility at multiple higher temperatures through the Fox Equation. Subsequently, a van't Hoff plot was constructed to estimate the drug solubility at room temperature, and the values were compared with those measured by HPLC. With the exception of Naproxen, room temperature solubilities of the remaining drug compounds in PEG 400 were determined by this thermal method approach, and compared with those measured by HPLC: 26.7% vs. 24.7% for Ibuprofen, 5.8% vs. 9.6% for Indomethacin, 3.1 % vs. 1.5% for PC-1, 2.3% vs. 1.3% for PC-2, and 1.4% vs. 0.2% for PC-3 in PEG 400. There was good concordance in solubility rank order estimates between the two methods. These collective results support the potential utility of the thermal method as an alternative to other methods for estimation of drug solubility in polymers which is an important determinant in the design of physically-stable amorphous systems.
Ruch, Nicole; Joss, Franziska; Jimmy, Gerda; Melzer, Katarina; Hänggi, Johanna; Mäder, Urs
2013-11-01
The aim of this study was to compare the energy expenditure (EE) estimations of activity-specific prediction equations (ASPE) and of an artificial neural network (ANNEE) based on accelerometry with measured EE. Forty-three children (age: 9.8 ± 2.4 yr) performed eight different activities. They were equipped with one tri-axial accelerometer that collected data in 1-s epochs and a portable gas analyzer. The ASPE and the ANNEE were trained to estimate the EE by including accelerometry, age, gender, and weight of the participants. To provide the activity-specific information, a decision tree was trained to recognize the type of activity through accelerometer data. The ASPE were applied to the activity-type-specific data recognized by the tree (Tree-ASPE). The Tree-ASPE precisely estimated the EE of all activities except cycling [bias: -1.13 ± 1.33 metabolic equivalent (MET)] and walking (bias: 0.29 ± 0.64 MET; P MET) and walking (bias: 0.61 ± 0.72 MET) and underestimated the EE of cycling (bias: -0.90 ± 1.18 MET; P MET, Tree-ASPE: 0.08 ± 0.21 MET) and walking (ANNEE 0.61 ± 0.72 MET, Tree-ASPE: 0.29 ± 0.64 MET) were significantly smaller in the Tree-ASPE than in the ANNEE (P < 0.05). The Tree-ASPE was more precise in estimating the EE than the ANNEE. The use of activity-type-specific information for subsequent EE prediction equations might be a promising approach for future studies.
Stable estimation of two coefficients in a nonlinear Fisher-KPP equation
Cristofol, Michel; Roques, Lionel
2013-09-01
We consider the inverse problem of determining two non-constant coefficients in a nonlinear parabolic equation of the Fisher-Kolmogorov-Petrovsky-Piskunov type. For the equation ut = DΔu + μ(x) u - γ(x)u2 in (0, T) × Ω, which corresponds to a classical model of population dynamics in a bounded heterogeneous environment, our results give a stability inequality between the couple of coefficients (μ, γ) and some observations of the solution u. These observations consist in measurements of u: in the whole domain Ω at two fixed times, in a subset ω⊂⊂Ω during a finite time interval and on the boundary of Ω at all times t ∈ (0, T). The proof relies on parabolic estimates together with the parabolic maximum principle and Hopf’s lemma which enable us to use a Carleman inequality. This work extends previous studies on the stable determination of non-constant coefficients in parabolic equations, as it deals with two coefficients and with a nonlinear term. A consequence of our results is the uniqueness of the couple of coefficients (μ, γ), given the observation of u. This uniqueness result was obtained in a previous paper but in the one-dimensional case only.
Asquith, William H.; Thompson, David B.
2008-01-01
The U.S. Geological Survey, in cooperation with the Texas Department of Transportation and in partnership with Texas Tech University, investigated a refinement of the regional regression method and developed alternative equations for estimation of peak-streamflow frequency for undeveloped watersheds in Texas. A common model for estimation of peak-streamflow frequency is based on the regional regression method. The current (2008) regional regression equations for 11 regions of Texas are based on log10 transformations of all regression variables (drainage area, main-channel slope, and watershed shape). Exclusive use of log10-transformation does not fully linearize the relations between the variables. As a result, some systematic bias remains in the current equations. The bias results in overestimation of peak streamflow for both the smallest and largest watersheds. The bias increases with increasing recurrence interval. The primary source of the bias is the discernible curvilinear relation in log10 space between peak streamflow and drainage area. Bias is demonstrated by selected residual plots with superimposed LOWESS trend lines. To address the bias, a statistical framework based on minimization of the PRESS statistic through power transformation of drainage area is described and implemented, and the resulting regression equations are reported. Compared to log10-exclusive equations, the equations derived from PRESS minimization have PRESS statistics and residual standard errors less than the log10 exclusive equations. Selected residual plots for the PRESS-minimized equations are presented to demonstrate that systematic bias in regional regression equations for peak-streamflow frequency estimation in Texas can be reduced. Because the overall error is similar to the error associated with previous equations and because the bias is reduced, the PRESS-minimized equations reported here provide alternative equations for peak-streamflow frequency estimation.
Directory of Open Access Journals (Sweden)
Abdollah BORHANIFAR
2013-01-01
Full Text Available In this study fractional Poisson equation is scrutinized through finite difference using shifted Grünwald estimate. A novel method is proposed numerically. The existence and uniqueness of solution for the fractional Poisson equation are proved. Exact and numerical solution are constructed and compared. Then numerical result shows the efficiency of the proposed method.
Directory of Open Access Journals (Sweden)
Patrick Addo-Fordjour
2013-01-01
Full Text Available The study developed allometric equations for estimating liana stem and total above-ground biomass in primary and secondary forests in the Penang National Park, Penang, Malaysia. Using biomass-diameter-length data of 60 liana individuals representing 15 species, allometric equations were developed for liana stem biomass and total above-ground biomass (TAGB. Three types of allometric equations were developed: models fitted to untransformed, weighted, and log-transformed (log10 data. There was a significant linear relationship between biomass and the predictors (diameter, length, and/or their combinations. The same set of models was developed for primary and secondary forests due to absence of differences in regression line slopes of the forests (ANCOVA: . The coefficients of determination values of the models were high (stem: 0.861 to 0.990; TAGB: 0.900 to 0.992. Generally, log-transformed models showed better fit (Furnival's index, FI 0.5. A comparison of the best TAGB model in this study (based on FI with previously published equations indicated that most of the equations significantly ( overestimated TAGB of lianas. However, a previous equation from Southeast Asia estimated TAGB similar to that of the current equation (. Therefore, regional or intracontinental equations should be preferred to intercontinental equations when estimating liana biomass.
Optimal experiment selection for parameter estimation in biological differential equation models
Directory of Open Access Journals (Sweden)
Transtrum Mark K
2012-07-01
Full Text Available Abstract Background Parameter estimation in biological models is a common yet challenging problem. In this work we explore the problem for gene regulatory networks modeled by differential equations with unknown parameters, such as decay rates, reaction rates, Michaelis-Menten constants, and Hill coefficients. We explore the question to what extent parameters can be efficiently estimated by appropriate experimental selection. Results A minimization formulation is used to find the parameter values that best fit the experiment data. When the data is insufficient, the minimization problem often has many local minima that fit the data reasonably well. We show that selecting a new experiment based on the local Fisher Information of one local minimum generates additional data that allows one to successfully discriminate among the many local minima. The parameters can be estimated to high accuracy by iteratively performing minimization and experiment selection. We show that the experiment choices are roughly independent of which local minima is used to calculate the local Fisher Information. Conclusions We show that by an appropriate choice of experiments, one can, in principle, efficiently and accurately estimate all the parameters of gene regulatory network. In addition, we demonstrate that appropriate experiment selection can also allow one to restrict model predictions without constraining the parameters using many fewer experiments. We suggest that predicting model behaviors and inferring parameters represent two different approaches to model calibration with different requirements on data and experimental cost.
Energy Technology Data Exchange (ETDEWEB)
Almorox, J.; Hontoria, C. [Universidad Politecnica de Madrid (Spain). Dpto. De Edafologia; Benito, M. [Universidad Politecnica de Madrid (Spain). Dpto. De Silvopasicultura
2005-05-01
In this study, daily global radiation for Toledo (39{sup o}53'05''N, 4{sup o}02'58''W, Spain) were utilized to determine monthly-specific equations for estimating global solar radiation from sunshine hours and to obtain improved fits to monthly Angstrom-Prescott's coefficients. Models were compared using the root mean square error (RMSE), the mean bias error (MBE) and the t-statistic. According to our results, all the models fitted the data adequately and can be used to estimate the specific monthly global solar radiation. Average RMSE and MBE for comparison between observed and estimated global radiation were 1.260 and -0.002 MJ m{sup -2} day{sup -1}, respectively. The t-statistic was used as the best indicator, this indicator depends on both, and is more effective for determining the model performance. The agreement between the estimated and the measured data were remarkable and the method was recommended for use in Toledo (Spain). (author)
Nonparametric Estimates of Gene × Environment Interaction Using Local Structural Equation Modeling
Briley, Daniel A.; Harden, K. Paige; Bates, Timothy C.; Tucker-Drob, Elliot M.
2017-01-01
Gene × Environment (G×E) interaction studies test the hypothesis that the strength of genetic influence varies across environmental contexts. Existing latent variable methods for estimating G×E interactions in twin and family data specify parametric (typically linear) functions for the interaction effect. An improper functional form may obscure the underlying shape of the interaction effect and may lead to failures to detect a significant interaction. In this article, we introduce a novel approach to the behavior genetic toolkit, local structural equation modeling (LOSEM). LOSEM is a highly flexible nonparametric approach for estimating latent interaction effects across the range of a measured moderator. This approach opens up the ability to detect and visualize new forms of G×E interaction. We illustrate the approach by using LOSEM to estimate gene × socioeconomic status (SES) interactions for six cognitive phenotypes. Rather than continuously and monotonically varying effects as has been assumed in conventional parametric approaches, LOSEM indicated substantial nonlinear shifts in genetic variance for several phenotypes. The operating characteristics of LOSEM were interrogated through simulation studies where the functional form of the interaction effect was known. LOSEM provides a conservative estimate of G×E interaction with sufficient power to detect statistically significant G×E signal with moderate sample size. We offer recommendations for the application of LOSEM and provide scripts for implementing these biometric models in Mplus and in OpenMx under R. PMID:26318287
Nam, Vu Thanh; van Kuijk, Marijke; Anten, Niels P R
2016-01-01
Allometric regression models are widely used to estimate tropical forest biomass, but balancing model accuracy with efficiency of implementation remains a major challenge. In addition, while numerous models exist for aboveground mass, very few exist for roots. We developed allometric equations for aboveground biomass (AGB) and root biomass (RB) based on 300 (of 45 species) and 40 (of 25 species) sample trees respectively, in an evergreen forest in Vietnam. The biomass estimations from these local models were compared to regional and pan-tropical models. For AGB we also compared local models that distinguish functional types to an aggregated model, to assess the degree of specificity needed in local models. Besides diameter at breast height (DBH) and tree height (H), wood density (WD) was found to be an important parameter in AGB models. Existing pan-tropical models resulted in up to 27% higher estimates of AGB, and overestimated RB by nearly 150%, indicating the greater accuracy of local models at the plot level. Our functional group aggregated local model which combined data for all species, was as accurate in estimating AGB as functional type specific models, indicating that a local aggregated model is the best choice for predicting plot level AGB in tropical forests. Finally our study presents the first allometric biomass models for aboveground and root biomass in forests in Vietnam.
Mindikoglu, Ayse L.; Dowling, Thomas C.; Weir, Matthew R.; Seliger, Stephen L.; Christenson, Robert H.; Magder, Laurence S.
2013-01-01
Conventional creatinine-based glomerular filtration rate (GFR) equations are insufficiently accurate for estimating GFR in cirrhosis. The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) recently proposed an equation to estimate GFR in subjects without cirrhosis using both serum creatinine and cystatin C levels. Performance of the new CKD-EPI creatinine-cystatin C equation (2012) was superior to previous creatinine- or cystatin C-based GFR equations. To evaluate the performance of the CKD-EPI creatinine-cystatin C equation in subjects with cirrhosis, we compared it to GFR measured by non-radiolabeled iothalamate plasma clearance (mGFR) in 72 subjects with cirrhosis. We compared the “bias”, “precision” and “accuracy” of the new CKD-EPI creatinine-cystatin C equation to that of 24-hour urinary creatinine clearance (CrCl), Cockcroft-Gault (CG) and previously reported creatinine- and/or cystatin C-based GFR-estimating equations. Accuracy of CKD-EPI creatinine-cystatin C equation as quantified by root mean squared error of difference scores [differences between mGFR and estimated GFR (eGFR) or between mGFR and CrCl, or between mGFR and CG equation for each subject] (RMSE=23.56) was significantly better than that of CrCl (37.69, P=0.001), CG (RMSE=36.12, P=0.002) and GFR-estimating equations based on cystatin C only. Its accuracy as quantified by percentage of eGFRs that differed by greater than 30% with respect to mGFR was significantly better compared to CrCl (P=0.024), CG (P=0.0001), 4-variable MDRD (P=0.027) and CKD-EPI creatinine 2009 (P=0.012) equations. However, for 23.61% of the subjects, GFR estimated by CKD-EPI creatinine-cystatin C equation differed from the mGFR by more than 30%. CONCLUSIONS The diagnostic performance of CKD-EPI creatinine-cystatin C equation (2012) in patients with cirrhosis was superior to conventional equations in clinical practice for estimating GFR. However, its diagnostic performance was substantially worse than
The use of generalized estimating equations in the analysis of motor vehicle crash data.
Hutchings, Caroline B; Knight, Stacey; Reading, James C
2003-01-01
The purpose of this study was to determine if it is necessary to use generalized estimating equations (GEEs) in the analysis of seat belt effectiveness in preventing injuries in motor vehicle crashes. The 1992 Utah crash dataset was used, excluding crash participants where seat belt use was not appropriate (n=93,633). The model used in the 1996 Report to Congress [Report to congress on benefits of safety belts and motorcycle helmets, based on data from the Crash Outcome Data Evaluation System (CODES). National Center for Statistics and Analysis, NHTSA, Washington, DC, February 1996] was analyzed for all occupants with logistic regression, one level of nesting (occupants within crashes), and two levels of nesting (occupants within vehicles within crashes) to compare the use of GEEs with logistic regression. When using one level of nesting compared to logistic regression, 13 of 16 variance estimates changed more than 10%, and eight of 16 parameter estimates changed more than 10%. In addition, three of the independent variables changed from significant to insignificant (alpha=0.05). With the use of two levels of nesting, two of 16 variance estimates and three of 16 parameter estimates changed more than 10% from the variance and parameter estimates in one level of nesting. One of the independent variables changed from insignificant to significant (alpha=0.05) in the two levels of nesting model; therefore, only two of the independent variables changed from significant to insignificant when the logistic regression model was compared to the two levels of nesting model. The odds ratio of seat belt effectiveness in preventing injuries was 12% lower when a one-level nested model was used. Based on these results, we stress the need to use a nested model and GEEs when analyzing motor vehicle crash data.
Directory of Open Access Journals (Sweden)
Adom Giffin
2014-09-01
Full Text Available In this paper, we continue our efforts to show how maximum relative entropy (MrE can be used as a universal updating algorithm. Here, our purpose is to tackle a joint state and parameter estimation problem where our system is nonlinear and in a non-equilibrium state, i.e., perturbed by varying external forces. Traditional parameter estimation can be performed by using filters, such as the extended Kalman filter (EKF. However, as shown with a toy example of a system with first order non-homogeneous ordinary differential equations, assumptions made by the EKF algorithm (such as the Markov assumption may not be valid. The problem can be solved with exponential smoothing, e.g., exponentially weighted moving average (EWMA. Although this has been shown to produce acceptable filtering results in real exponential systems, it still cannot simultaneously estimate both the state and its parameters and has its own assumptions that are not always valid, for example when jump discontinuities exist. We show that by applying MrE as a filter, we can not only develop the closed form solutions, but we can also infer the parameters of the differential equation simultaneously with the means. This is useful in real, physical systems, where we want to not only filter the noise from our measurements, but we also want to simultaneously infer the parameters of the dynamics of a nonlinear and non-equilibrium system. Although there were many assumptions made throughout the paper to illustrate that EKF and exponential smoothing are special cases ofMrE, we are not “constrained”, by these assumptions. In other words, MrE is completely general and can be used in broader ways.
Baker, Charles
2012-01-01
One method available to prove the Schauder estimates is Neil Trudinger's method of mollification. In the case of second order elliptic equations, the method requires little more than mollification and the solid mean value inequality for subharmonic functions. Our goal in this article is show how the mean value property of subsolutions of the heat equation can be used in a similar fashion as the solid mean value inequality for subharmonic functions in Trudinger's original elliptic treatment, providing a relatively simple derivation of the interior Schauder estimate for second order parabolic equations.
Cirmi, G. Rita; D'Asero, Salvatore; Leonardi, Salvatore
2017-07-01
We study the regularity of a solution of the Dirichlet problem associated to the singular equation -div(a (x )D u )+M |/D u | uθ =f (x )inΩ (1) where Ω is an open bounded subset of ℝN (N ≥ 3) with smooth boundary, a(x) is a L∞ -matrix satisfying the standard ellipticity condition, θ ∈]0, 1[, M is a positive constant and f is sufficiently regular i.e. it belongs to a suitable Morrey space Lq,λ (Ω), with q ≥ 1, to be specified later on. We will be concerned with the regularity of the gradient of a solution in Morrey spaces in correspondence with the regularity properties of the right-hand side of the equation (1). There is a huge literature about the problems with quadratic term in the gradient also for high-order equations whose coefficients satisfy a strengthened ellipticity condition (see [5]). The problem (1) has been studied in the paper [2] by D. Arcoya, J. Carmona, T. Leonori, P. J. Martínez-Aparicio, L. Orsina, F. Petitta and in the paper [3] by L. Boccardo where the source term f belonged to Lq(Ω) with q ≥ 1. In [4] we have extended to the gradient of a solution the Morrey property of the right-hand side f and, in some cases, we have improved some results contained in [2, 3] without increasing the summability of f. Here we will be concerned with an intermediate case, in the sense that the right hand side is not merely a measure and it doesn't belong to the right dual space (see [10, 9]). In obtaining the necessary local estimates we faced the problem of performing the Campanato's decomposition of the solution due to the presence of the degenerate lower order term. We had thus to adopt an alternative method already used in [4]. This is part of a new set of estimates, including potential estimates, as for instance in [6, 7, 8], that would be very interesting to extend in the present setting too.
Estimating the Risk of Renal Stone Events During Long-Duration Spaceflight
Reyes, David; Kerstman, Eric; Locke, James
2014-01-01
Introduction: Given the bone loss and increased urinary calcium excretion in the microgravity environment, persons participating in long-duration spaceflight may have an increased risk for renal stone formation. Renal stones are often an incidental finding of abdominal imaging studies done for other reasons. Thus, some crewmembers may have undiscovered, asymptomatic stones prior to their mission. Methods: An extensive literature search was conducted concerning the natural history of asymptomatic renal stones. For comparison, simulations were done using the Integrated Medical Model (IMM). The IMM is an evidence-based decision support tool that provides risk analysis and has the capability to optimize medical systems for missions by minimizing the occurrence of adverse mission outcomes such as evacuation and loss of crew life within specified mass and volume constraints. Results: The literature of the natural history of asymptomatic renal stones in the general medical population shows that the probability of symptomatic event is 8% to 34% at 1 to 3 years for stones renal stones may be one of the top drivers for medical evacuation of an International Space Station (ISS) mission. Discussion: Although the likelihood of a stone event is low, the consequences could be severe due to limitations of current ISS medical capabilities. Therefore, these risks need to be quantified to aid planning, limit crew morbidity and mitigate mission impacts. This will be especially critical for missions beyond earth orbit, where evacuation may not be an option.
Parameter estimation for stiff equations of biosystems using radial basis function networks
Directory of Open Access Journals (Sweden)
Sugimoto Masahiro
2006-04-01
Full Text Available Abstract Background The modeling of dynamic systems requires estimating kinetic parameters from experimentally measured time-courses. Conventional global optimization methods used for parameter estimation, e.g. genetic algorithms (GA, consume enormous computational time because they require iterative numerical integrations for differential equations. When the target model is stiff, the computational time for reaching a solution increases further. Results In an attempt to solve this problem, we explored a learning technique that uses radial basis function networks (RBFN to achieve a parameter estimation for biochemical models. RBFN reduce the number of numerical integrations by replacing derivatives with slopes derived from the distribution of searching points. To introduce a slight search bias, we implemented additional data selection using a GA that searches data-sparse areas at low computational cost. In addition, we adopted logarithmic transformation that smoothes the fitness surface to obtain a solution simply. We conducted numerical experiments to validate our methods and compared the results with those obtained by GA. We found that the calculation time decreased by more than 50% and the convergence rate increased from 60% to 90%. Conclusion In this work, our RBFN technique was effective for parameter optimization of stiff biochemical models.
Methods and equations for estimating peak streamflow per square mile in Virginia’s urban basins
Austin, Samuel H.
2014-01-01
Models are presented that describe Virginia urban area annual peak streamflow per square mile based on basin percent urban area and basin drainage area. Equations are provided to estimate Virginia urban peak flow per square mile of basin drainage area in each of the following annual exceedance probability categories: 0.995, 0.99, 0.95, 0.9, 0.8, 0.67, 0.5, 0.43, 0.2, 0.1, 0.04, 0.02, 0.01, 0.005, and 0.002 (recurrence intervals of 1.005, 1.01, 1.05, 1.11, 1.25, 1.49, 2.0, 2.3, 5, 10, 25, 50, 100, 200, and 500 years, respectively). Equations apply to Virginia drainage basins ranging in size from no less than 1.2 mi2 to no more than 2,400 mi2 containing at least 10 percent urban area, and not more than 96 percent urban area. A total of 115 Virginia drainage basins were analyzed. Actual-by-predicted plots and leverage plots for response variables and explanatory variables in each peak-flow annual exceedance probability category indicate robust model fits and significant explanatory power. Equations for 8 of 15 urban peak-flow response surface models yield R-square values greater than 0.8. Relations identified in statistical models, describing significant increases in urban peak stream discharges as basin urban area increases, affirm empirical relations reported in past studies of change in stream discharge, lag times, and physical streamflow processes, most notably those detailed for urban areas in northern Virginia.
Regularization and error estimates for asymmetric backward nonhomogeneous heat equations in a ball
Directory of Open Access Journals (Sweden)
Le Minh Triet
2016-09-01
Full Text Available The backward heat problem (BHP has been researched by many authors in the last five decades; it consists in recovering the initial distribution from the final temperature data. There are some articles [1,2,3] related the axi-symmetric BHP in a disk but the study in spherical coordinates is rare. Therefore, we wish to study a backward problem for nonhomogenous heat equation associated with asymmetric final data in a ball. In this article, we modify the quasi-boundary value method to construct a stable approximate solution for this problem. As a result, we obtain regularized solution and a sharp estimates for its error. At the end, a numerical experiment is provided to illustrate our method.
Simple equation for estimating actual evapotranspiration using heat units for wheat in arid regions
Directory of Open Access Journals (Sweden)
M.A. Salama
2015-07-01
Application of treatment (B resulted in highly significant increase in yield production of Gemmeza10 and Misr2 as compared to treatment (A. Grain yield of different wheat varieties grown under treatment (B could be ranked in the following descending order: Misr2 > Gemmeza10 > Sids12. While under treatment (A it could be arranged in the following descending order: Misr2 > Sids12 > Gemmeza10. On the other hand, the overall means indicated non-significant difference between all wheat verities. The highest values of water and irrigation use efficiency as well as heat use efficiency were obtained with treatment (B. The equation used in the present study is available to estimate ETa under arid climate with drip irrigation system.
Least Orthogonal Distance Estimator and Total Least Square for Simultaneous Equation Models
Directory of Open Access Journals (Sweden)
Alessia Naccarato
2014-01-01
Full Text Available Least Orthogonal Distance Estimator (LODE of Simultaneous Equation Models’ structural parameters is based on minimizing the orthogonal distance between Reduced Form (RF and the Structural Form (SF parameters. In this work we propose a new version – with respect to Pieraccini and Naccarato (2008 – of Full Information (FI LODE based on decomposition of a new structure of the variance-covariance matrix using Singular Value Decomposition (SVD instead of Spectral Decomposition (SD. In this context Total Least Square is applied. A simulation experiment to compare the performances of the new version of FI LODE with respect to Three Stage Least Square (3SLS and Full Information Maximum Likelihood (FIML is presented. Finally a comparison between the FI LODE new and old version together with few words of conclusion conclude the paper.
IQ heritability estimation: analyzing genetically-informative data with structural equation models.
Gallardo Pujol, David; García-Forero, Carlos; Kramp, Uwe; Maydeu-Olivares, Albert; Andrés-Pueyo, Antonio
2007-02-01
When analyzing genetic data, Structural Equations Modeling (SEM) provides a straightforward methodology to decompose phenotypic variance using a model-based approach. Furthermore, several models can be easily implemented, tested, and compared using SEM, allowing the researcher to obtain valuable information about the sources of variability. This methodology is briefly described and applied to re-analyze a Spanish set of IQ data using the biometric ACE model. In summary, we report heritability estimates that are consistent with those of previous studies and support substantial genetic contribution to phenotypic IQ; around 40% of the variance can be attributable to it. With regard to the environmental contribution, shared environment accounts for 50% of the variance, and non-shared environment accounts for the remaining 10%. These results are discussed in the text.
Matsuoka, Susumu; Tominaga, Yoshihiro; Sato, Tetsuhiko; Uno, Nobuaki; Hiramitu, Takahisa; Goto, Norihiko; Nagasaka, Takaharu; Uchida, Kazuharu
2008-10-01
In renal hyperparathyroidism (HPT), the parathyroid glands initially proliferate diffusely and polyclonally, and are then transformed to monoclonal nodular hyperplasia with aggressive growth potential. In this study we evaluated the relationship between the maximal dimension of parathyroid glands estimated by ultrasonography (US) and the hyperplastic pattern of parathyroid glands in patients with renal HPT. Between October 1999 and December 2006, 141 patients who underwent total parathyroidectomy (PTx) with forearm autograft in our department were enrolled in this study. In these patients 308 parathyroid glands were detected by US before PTx. The largest dimension of the gland estimated preoperatively by US was correlated closely with its measurement at surgery (R2 was 0.31, P parathyroid hyperplasia and the glandular diameter when we defined 8 mm as the maximal diameter estimated by US as a cut-off value. As a result of receiver operating characteristic analyses, using these criteria the US technique could predict nodular hyperplasia with a high sensitivity (78.9%) and specificity (78.7%). Parathyroid glands that are enlarged by more than 8 mm in the largest dimension estimated by US may represent glands with nodular hyperplasia.
Nikoloulopoulos, Aristidis K
2016-06-30
The method of generalized estimating equations (GEE) is popular in the biostatistics literature for analyzing longitudinal binary and count data. It assumes a generalized linear model for the outcome variable, and a working correlation among repeated measurements. In this paper, we introduce a viable competitor: the weighted scores method for generalized linear model margins. We weight the univariate score equations using a working discretized multivariate normal model that is a proper multivariate model. Because the weighted scores method is a parametric method based on likelihood, we propose composite likelihood information criteria as an intermediate step for model selection. The same criteria can be used for both correlation structure and variable selection. Simulations studies and the application example show that our method outperforms other existing model selection methods in GEE. From the example, it can be seen that our methods not only improve on GEE in terms of interpretability and efficiency but also can change the inferential conclusions with respect to GEE. Copyright © 2016 John Wiley & Sons, Ltd.
Estimates for the Large Time Behavior of the Landau Equation in the Coulomb Case
Carrapatoso, Kleber; Desvillettes, Laurent; He, Lingbing
2017-05-01
This work deals with the large time behaviour of the spatially homogeneous Landau equation with Coulomb potential. Firstly, we obtain a bound from below of the entropy dissipation D( f) by weighted relative Fisher information of f with respect to the associated Maxwellian distribution, which leads to a variant of Cercignani's conjecture thanks to a logarithmic Sobolev inequality. Secondly, we prove the propagation of polynomial and stretched exponential moments with an at-most linearly growing in-time rate. As an application of these estimates, we show the convergence of any ( H- or weak) solution to the Landau equation with Coulomb potential to the associated Maxwellian equilibrium with an explicitly computable rate, assuming initial data with finite mass, energy, entropy and some higher L 1-moment. More precisely, if the initial data have some (large enough) polynomial L 1-moment, then we obtain an algebraic decay. If the initial data have a stretched exponential L 1-moment, then we recover a stretched exponential decay.
A modelling on estimation of the carbon dioxide emission from vehicles using logistic equation
Chandra, E. W.; Andry, A.; Afra, F.; Sumarti, N.
2016-04-01
In this paper, the logistic differential equation is used in developing a model on carbon dioxide traces which potentially releases from a particular area. The improvement to a higher scale or scope is straightforward by considering the larger observed data or larger number of the potential CO2 sources. Let G(t) the total amount of the carbon dioxide emission from motorcycles and cars used by the resident of the area. G (t )=P (t )(r1(t )η (t )+r2(t )ξ (t )) where P(t) is the number of the resident of the observed area (population of Bandung Institute of Technology) at year t, r1(t) and r2(t) are the portion of the population who use motorcycles and cars respectively, η(t) and ξ(t) are the approximated total emission of the carbon dioxide from the related vehicles respectively. The number of resident is modeled by the logistic equation so the future number can be estimated. The model is implemented in a campus of Institut Teknologi Bandung (ITB) at Ganesha street, Indonesia. The results show that the amount of CO2 produced from the transport in Ganesha campus will reach the carrying capacity of the campus in the next 3 years, which will be at around 2.1 billion kilotons of CO2. Therefore, the need of reducing the usage of motorcycles and cars is inevitable in the near future.
Dang, Mia; Ramsaran, Kalinda D; Street, Melissa E; Syed, S Noreen; Barclay-Goddard, Ruth; Stratford, Paul W; Miller, Patricia A
2011-01-01
To estimate the predictive accuracy and clinical usefulness of the Chedoke-McMaster Stroke Assessment (CMSA) predictive equations. A longitudinal prognostic study using historical data obtained from 104 patients admitted post cerebrovascular accident was undertaken. Data were abstracted for all patients undergoing rehabilitation post stroke who also had documented admission and discharge CMSA scores. Published predictive equations were used to determine predicted outcomes. To determine the accuracy and clinical usefulness of the predictive model, shrinkage coefficients and predictions with 95% confidence bands were calculated. Complete data were available for 74 patients with a mean age of 65.3±12.4 years. The shrinkage values for the six Impairment Inventory (II) dimensions varied from -0.05 to 0.09; the shrinkage value for the Activity Inventory (AI) was 0.21. The error associated with predictive values was greater than ±1.5 stages for the II dimensions and greater than ±24 points for the AI. This study shows that the large error associated with the predictions (as defined by the confidence band) for the CMSA II and AI limits their clinical usefulness as a predictive measure. Further research to establish predictive models using alternative statistical procedures is warranted.
Directory of Open Access Journals (Sweden)
Oksana G. Cherniukh
2015-03-01
Full Text Available Creatitine clearance (CC by Reberg-Tareyev test has been analyzed with an essential condition to take urine analysis during 24 hours from pregnant women with various degree of preeclampsia. To characterize the renal excretory function in the regulation of nitrogen balance the indices of proteinemia and proteinuria have been used. Probable changes of the renal functional condition depending on the volume of 24-hour diuresis have been found. The necessity to analyze the indices using the standards for the pregnant according to the trimester of pregnancy is indicated.
Harry V., Jr. Wiant; Michael L. Spangler; John E. Baumgras
2002-01-01
Various taper systems and the centroid method were compared to unbiased volume estimates made by importance sampling for 720 hardwood trees selected throughout the state of West Virginia. Only the centroid method consistently gave volumes estimates that did not differ significantly from those made by importance sampling, although some taper equations did well for most...
Institute of Scientific and Technical Information of China (English)
Xiaobing Feng; Haijun Wu
2008-01-01
This paper develops a posteriori error estimates of residual type for conforming and mixed finite element approximations of the fourth order Cahn-Hilliard equation ut +△ (ε△μ-ε-1f(u))=0. It is shown that the a posteriori error bounds depends on ε-1 only in some low polynomial order, instead of exponential order. Using these a posteriori error estimates, we construct an adaptive algorithm for computing the solution of the Cahn-Hilliard equation and its sharp interface limit, the Hele-Shaw flow. Numerical experiments are presented to show the robustness and effectiveness of the new error estimators and the proposed adaptive algorithm.
GOSWAMI, DEEPJYOTI
2014-01-01
AWe propose and analyse an alternate approach to a priori error estimates for the semidiscrete Galerkin approximation to a time-dependent parabolic integro-differential equation with nonsmooth initial data. The method is based on energy arguments combined with repeated use of time integration, but without using parabolic-type duality techniques. An optimal L2-error estimate is derived for the semidiscrete approximation when the initial data is in L2. A superconvergence result is obtained and then used to prove a maximum norm estimate for parabolic integro-differential equations defined on a two-dimensional bounded domain. © 2014 Australian Mathematical Society.
Moses, Tim
2008-01-01
Equating functions are supposed to be population invariant, meaning that the choice of subpopulation used to compute the equating function should not matter. The extent to which equating functions are population invariant is typically assessed in terms of practical difference criteria that do not account for equating functions' sampling…
Directory of Open Access Journals (Sweden)
Benedicto Vargas-Larreta
2017-07-01
Full Text Available This paper presents new equations for estimating above-ground biomass (AGB and biomass components of seventeen forest species in the temperate forests of northwestern Mexico. A data set corresponding to 1336 destructively sampled oak and pine trees was used to fit the models. The generalized method of moments was used to simultaneously fit systems of equations for biomass components and AGB, to ensure additivity. In addition, the carbon content of each tree component was calculated by the dry combustion method, in a TOC analyser. The results of cross-validation indicated that the fitted equations accounted for on average 91%, 82%, 83% and 76% of the observed variance in stem wood and stem bark, branch and foliage biomass, respectively, whereas the total AGB equations explained on average 93% of the total observed variance in AGB. The inclusion of total height (h or diameter at breast height2 × total height (d2h as a predictor in the d-only based equations systems slightly improved estimates for stem wood, stem bark and total above-ground biomass, and greatly improved the estimates produced by the branch and foliage biomass equations. The predictive power of the proposed equations is higher than that of existing models for the study area. The fitted equations were used to estimate stand level AGB stocks from data on growing stock in 429 permanent sampling plots. Three machine-learning techniques were used to model the estimated stand level AGB and carbon contents; the selected models were used to map the AGB and carbon distributions in the study area, for which mean values of respectively 129.84 Mg ha−1 and 63.80 Mg ha−1 were obtained.
Institute of Scientific and Technical Information of China (English)
Amir H Alavi; Ehsan Sadrossadat
2016-01-01
Rock masses are commonly used as the underlying layer of important structures such as bridges, dams and transportation constructions. The success of a foundation design for such structures mainly depends on the accuracy of estimating the bearing capacity of rock beneath them. Several traditional numerical approaches are proposed for the estimation of the bearing capacity of foundations resting on rock masses to avoid performing elaborate and expensive experimental studies. Despite this fact, there still exists a serious need to develop more robust predictive models. This paper proposes new nonlinear prediction models for the ultimate bearing capacity of shallow foundations resting on non-fractured rock masses using a novel evolutionary computational approach, called linear genetic programming. A comprehen-sive set of rock socket, centrifuge rock socket, plate load and large-scaled footing load test results is used to develop the models. In order to verify the validity of the models, the sensitivity analysis is conducted and discussed. The results indicate that the proposed models accurately characterize the bearing capacity of shallow foundations. The correlation coefficients between the experimental and predicted bearing capacity values are equal to 0.95 and 0.96 for the best LGP models. Moreover, the derived models reach a notably better prediction performance than the traditional equations.
Hellander, Andreas; Lawson, Michael J.; Drawert, Brian; Petzold, Linda
2014-06-01
The efficiency of exact simulation methods for the reaction-diffusion master equation (RDME) is severely limited by the large number of diffusion events if the mesh is fine or if diffusion constants are large. Furthermore, inherent properties of exact kinetic-Monte Carlo simulation methods limit the efficiency of parallel implementations. Several approximate and hybrid methods have appeared that enable more efficient simulation of the RDME. A common feature to most of them is that they rely on splitting the system into its reaction and diffusion parts and updating them sequentially over a discrete timestep. This use of operator splitting enables more efficient simulation but it comes at the price of a temporal discretization error that depends on the size of the timestep. So far, existing methods have not attempted to estimate or control this error in a systematic manner. This makes the solvers hard to use for practitioners since they must guess an appropriate timestep. It also makes the solvers potentially less efficient than if the timesteps were adapted to control the error. Here, we derive estimates of the local error and propose a strategy to adaptively select the timestep when the RDME is simulated via a first order operator splitting. While the strategy is general and applicable to a wide range of approximate and hybrid methods, we exemplify it here by extending a previously published approximate method, the diffusive finite-state projection (DFSP) method, to incorporate temporal adaptivity.
Hellander, Andreas; Lawson, Michael J; Drawert, Brian; Petzold, Linda
2015-01-01
The efficiency of exact simulation methods for the reaction-diffusion master equation (RDME) is severely limited by the large number of diffusion events if the mesh is fine or if diffusion constants are large. Furthermore, inherent properties of exact kinetic-Monte Carlo simulation methods limit the efficiency of parallel implementations. Several approximate and hybrid methods have appeared that enable more efficient simulation of the RDME. A common feature to most of them is that they rely on splitting the system into its reaction and diffusion parts and updating them sequentially over a discrete timestep. This use of operator splitting enables more efficient simulation but it comes at the price of a temporal discretization error that depends on the size of the timestep. So far, existing methods have not attempted to estimate or control this error in a systematic manner. This makes the solvers hard to use for practitioners since they must guess an appropriate timestep. It also makes the solvers potentially less efficient than if the timesteps are adapted to control the error. Here, we derive estimates of the local error and propose a strategy to adaptively select the timestep when the RDME is simulated via a first order operator splitting. While the strategy is general and applicable to a wide range of approximate and hybrid methods, we exemplify it here by extending a previously published approximate method, the Diffusive Finite-State Projection (DFSP) method, to incorporate temporal adaptivity. PMID:26865735
Scour depth estimation using an equation based on wind tunnel experiments
Directory of Open Access Journals (Sweden)
Tsutsui Takayuki
2016-01-01
Full Text Available Scour is the result of degradation and aggradation by wind or moving fluid in the front and back of a pole standing in sand, respectively, and is often observed at the bottom of bridge piers in rivers. In this study, we propose a method of estimating the scour depth around a cylindrical structure standing in sand. The relationships among the depth of the scour, the aspect ratio of the structure (= height/diameter, the fluid velocity, and the sand properties (particle size and density were determined experimentally using a wind tunnel. The experiments were carried out under clear-water scour conditions. In the experiments, the aspect ratio of the cylindrical structure, the fluid velocity, and the sand particle size were varied systematically. The diameters of the structure were 20, 40, and 60 mm, and the aspect ratio was varied from 0.25 to 3.0. Sand particles of four sizes (200, 275, 475, and 600 μm were used in the experiment, and the velocity was varied from 4 to 11 m/s. The depth and radius of the scour were measured. As a result, we have developed an equation for estimating the scour depth that uses the aspect ratio, fluid velocity, and sand particle size as parameters.
Blufpand, Hester N; Westland, Rik; van Wijk, Joanna A E; Roelandse-Koop, Elianne A; Kaspers, Gertjan J L; Bökenkamp, Arend
2013-12-01
To compare the diagnostic performance of 2 height-independent equations used to calculate estimated glomerular filtration rate (eGFR), those of Pottel (eGFR-Pottel) and the British Columbia Children's Hospital (BCCH) (eGFR-BCCH), with the commonly used Schwartz equation (eGFR-Schwartz). We externally validated eGFR-Pottel and eGFR-BCCH in a well-characterized pediatric patient population (n = 152) and compared their diagnostic performance with that of eGFR-Schwartz using Bland-Altman analysis. All patients underwent glomerular filtration rate measurement using the gold standard single-injection inulin clearance method (GFR-inulin). Median GFR-inulin was 92.0 mL/min/1.73 m² (IQR, 76.1-107.4 mL/min/1.73 m²). Compared with GFR-inulin, the mean bias for eGFR-Schwartz was -10.1 mL/min/1.73 m(2) (95% limits of agreement [LOA], -77.5 to 57.2 mL/min/1.73 m(2)), compared with -12.3 mL/min/1.73 m² (95% LOA, -72.6 to 47.9 mL/min/1.73 m(2)) for eGFR-Pottel and -22.1 mL/min/1.73 m² (95% LOA, -105.0 to 60.8 mL/min/1.73 m(2)) for eGFR-BCCH. eGFR-Pottel showed comparable accuracy to eGFR-Schwartz, with 77% and 76% of estimates within 30% of GFR-inulin, respectively. eGFR-BCCH was less accurate than eGFR-Schwartz (66% of estimates within 30% of GFR-inulin; P Schwartz. eGFR-Pottel is a valid alternative to eGFR-Schwartz in children and could be reported by the laboratory if height data are not available. Copyright © 2013 Mosby, Inc. All rights reserved.
Directory of Open Access Journals (Sweden)
Xun Liu
2014-01-01
Full Text Available Objectives. To evaluate eight modified equations developed in Asiatic populations in type 2 diabetic patients in China. Methods. A total of 209 Chinese patients with type 2 diabetes were recruited. Using the technetium—99m diethylenetriaminepentaacetic acid—glomerular filtration rate (GFR to act as the reference, comparisons of their efficiency to estimate GFR in the subjects were made between various equations. Results. Median of difference of the Chinese equation 1 was the lowest (median of difference, 0.51 mL/min/1.73 m2. Median percent of absolute difference of the Chinese equation 2 was less than those of the other equations (26.97 versus ranged from 32.54 to 37.61 mL/min/1.73 m2, [P<0.001 for all]. Precision of the simplified reexpressed MDRD equation was the best (92.9 mL/min/1.73 m2. Accuracies of the Chinese equation 2 were greater (P<0.05 for all. There was also an improvement in chronic kidney disease (CKD stage misclassification of the Chinese equation 2 (55.0 versus ranged from 61.2 to 64.6%, [P<0.001 for all]. However, the 30% accuracies of all the equations were less than 70%. Conclusions. Our study highlighted a limitation in the use of the above equations in the majority of Chinese diabetic subjects. A better equation is needed in order to give an accurate estimation of GFR in type 2 diabetic patients in China.
DEFF Research Database (Denmark)
Andersen, Trine Borup; Jødal, Lars; Bøgsted, Martin
AIM: To derive an accurate prediction model for estimating glomerular filtration rate (GFR) in children based primarily on the endogenous renal function marker cystatin C (CysC) and body cell mass (BCM). THEORY: Cystatin C is produced at a constant rate in all cells of the body and is excreted...... by glomerular filtration followed by catabolization in the tubular cells. We hypothesized that production rate is proportional to body cell mass (BCM) and inferred GFR (mL/min) to be proportional to BCM/CysC. MATERIAL AND METHODS: GFR was determined with 51Cr-EDTA-clearance in 131 children (52 girls, 79 boys...
DEFF Research Database (Denmark)
Andersen, Trine Borup; Jødal, Lars; Bøgsted, Martin
AIM: To derive an accurate prediction model for estimating glomerular filtration rate (GFR) in children based primarily on the endogenous renal function marker cystatin C (CysC) and body cell mass (BCM). THEORY: Cystatin C is produced at a constant rate in all cells of the body and is excreted...... by glomerular filtration followed by catabolization in the tubular cells. We hypothesized that production rate is proportional to body cell mass (BCM) and inferred GFR (mL/min) to be proportional to BCM/CysC. MATERIAL AND METHODS: GFR was determined with 51Cr-EDTA-clearance in 131 children (52 girls, 79 boys...
Spatial Data Mining for Estimating Cover Management Factor of Universal Soil Loss Equation
Tsai, F.; Lin, T. C.; Chiang, S. H.; Chen, W. W.
2016-12-01
Universal Soil Loss Equation (USLE) is a widely used mathematical model that describes long-term soil erosion processes. Among the six different soil erosion risk factors of USLE, the cover-management factor (C-factor) is related to land-cover/land-use. The value of C-factor ranges from 0.001 to 1, so it alone might cause a thousandfold difference in a soil erosion analysis using USLE. The traditional methods for the estimation of USLE C-factor include in situ experiments, soil physical parameter models, USLE look-up tables with land use maps, and regression models between vegetation indices and C-factors. However, these methods are either difficult or too expensive to implement in large areas. In addition, the values of C-factor obtained using these methods can not be updated frequently, either. To address this issue, this research developed a spatial data mining approach to estimate the values of C-factor with assorted spatial datasets for a multi-temporal (2004 to 2008) annual soil loss analysis of a reservoir watershed in northern Taiwan. The idea is to establish the relationship between the USLE C-factor and spatial data consisting of vegetation indices and texture features extracted from satellite images, soil and geology attributes, digital elevation model, road and river distribution etc. A decision tree classifier was used to rank influential conditional attributes in the preliminary data mining. Then, factor simplification and separation were considered to optimize the model and the random forest classifier was used to analyze 9 simplified factor groups. Experimental results indicate that the overall accuracy of the data mining model is about 79% with a kappa value of 0.76. The estimated soil erosion amounts in 2004-2008 according to the data mining results are about 50.39 - 74.57 ton/ha-year after applying the sediment delivery ratio and correction coefficient. Comparing with estimations calculated with C-factors from look-up tables, the soil erosion
Wu, Hulin; Xue, Hongqi; Kumar, Arun
2012-06-01
Differential equations are extensively used for modeling dynamics of physical processes in many scientific fields such as engineering, physics, and biomedical sciences. Parameter estimation of differential equation models is a challenging problem because of high computational cost and high-dimensional parameter space. In this article, we propose a novel class of methods for estimating parameters in ordinary differential equation (ODE) models, which is motivated by HIV dynamics modeling. The new methods exploit the form of numerical discretization algorithms for an ODE solver to formulate estimating equations. First, a penalized-spline approach is employed to estimate the state variables and the estimated state variables are then plugged in a discretization formula of an ODE solver to obtain the ODE parameter estimates via a regression approach. We consider three different order of discretization methods, Euler's method, trapezoidal rule, and Runge-Kutta method. A higher-order numerical algorithm reduces numerical error in the approximation of the derivative, which produces a more accurate estimate, but its computational cost is higher. To balance the computational cost and estimation accuracy, we demonstrate, via simulation studies, that the trapezoidal discretization-based estimate is the best and is recommended for practical use. The asymptotic properties for the proposed numerical discretization-based estimators are established. Comparisons between the proposed methods and existing methods show a clear benefit of the proposed methods in regards to the trade-off between computational cost and estimation accuracy. We apply the proposed methods t an HIV study to further illustrate the usefulness of the proposed approaches.
Bahşı, Ayşe Kurt; Yalçınbaş, Salih
2016-01-01
In this study, the Fibonacci collocation method based on the Fibonacci polynomials are presented to solve for the fractional diffusion equations with variable coefficients. The fractional derivatives are described in the Caputo sense. This method is derived by expanding the approximate solution with Fibonacci polynomials. Using this method of the fractional derivative this equation can be reduced to a set of linear algebraic equations. Also, an error estimation algorithm which is based on the residual functions is presented for this method. The approximate solutions are improved by using this error estimation algorithm. If the exact solution of the problem is not known, the absolute error function of the problems can be approximately computed by using the Fibonacci polynomial solution. By using this error estimation function, we can find improved solutions which are more efficient than direct numerical solutions. Numerical examples, figures, tables are comparisons have been presented to show efficiency and usable of proposed method.
Directory of Open Access Journals (Sweden)
Eliane Lopes Rosado
2014-03-01
Full Text Available Objective: To assess the adequacy of predictive equations for estimation of energy expenditure (EE, compared with the EE using indirect calorimetry in a sample of Brazilian and Spanish women with excess body weight Methods: It is a cross-sectional study with 92 obese adult women [26 Brazilian -G1- and 66 Spanish - G2- (aged 20-50]. Weight and height were evaluated during fasting for the calculation of body mass index and predictive equations. EE was evaluated using the open-circuit indirect calorimetry with respiratory hood. Results: In G1 and G2, it was found that the estimates obtained by Harris-Benedict, Shofield, FAO/WHO/ ONU and Henry & Rees did not differ from EE using indirect calorimetry, which presented higher values than the equations proposed by Owen, Mifflin-St Jeor and Oxford. For G1 and G2 the predictive equation closest to the value obtained by the indirect calorimetry was the FAO/WHO/ONU (7.9% and 0.46% underestimation, respectively, followed by Harris-Benedict (8.6% and 1.5% underestimation, respectively. Conclusion: The equations proposed by FAO/WHO/ ONU, Harris-Benedict, Shofield and Henry & Rees were adequate to estimate the EE in a sample of Brazilian and Spanish women with excess body weight. The other equations underestimated the EE.
Gugushvili, Shota
2010-01-01
We consider the problem of parameter estimation for a system of ordinary differential equations from noisy observations on a solution of the system. In case the system is nonlinear, as it typically is in practical applications, an analytic solution to it usually does not exist. Consequently, straightforward estimation methods like the ordinary least squares method depend on repetitive use of numerical integration in order to determine the solution of the system for each of the parameter values considered, and to find subsequently the parameter estimate that minimises the objective function. This induces a huge computational load to such estimation methods. We propose an estimator that is defined as a minimiser of an appropriate distance between a nonparametrically estimated derivative of the solution and the right-hand side of the system applied to a nonparametrically estimated solution. Our estimator bypasses numerical integration altogether and reduces the amount of computational time drastically compared t...
Asiri, Sharefa M.
2016-10-20
In this paper, modulating functions-based method is proposed for estimating space–time-dependent unknowns in one-dimensional partial differential equations. The proposed method simplifies the problem into a system of algebraic equations linear in unknown parameters. The well-posedness of the modulating functions-based solution is proved. The wave and the fifth-order KdV equations are used as examples to show the effectiveness of the proposed method in both noise-free and noisy cases.
Comparison of estimated glomerular filtration rate equations at the time of hemodialysis initiation
Directory of Open Access Journals (Sweden)
Min-Jeong Lee
2015-12-01
Conclusions: The eGFR at HD initiation are significantly different according to the used eGFR equations, and the corrected Cockcroft–Gault equation may be the best in defining the eGFR at HD initiation.
Altunbas, Gokhan; Yazc, Mehmet; Solak, Yalcin; Gul, Enes E; Kayrak, Mehmet; Kaya, Zeynettin; Akilli, Hakan; Aribas, Alpay; Gaipov, Abduzhappar; Yazc, Raziye; Ozdemir, Kurtulus
2016-01-01
It is of clinical importance to determine creatinine clearance and adjust doses of prescribed drugs accordingly in patients with heart failure to prevent untoward effects. There is a scarcity of studies in the literature investigating this issue particularly in patients with heart failure, in whom many have impaired kidney function. The purpose of this study was to determine the degree of awareness of medication prescription as to creatinine clearance in patients hospitalized with heart failure. Patients hospitalized with a diagnosis of heart failure were retrospectively evaluated. Among screened charts, patients with left ventricular ejection fraction renal dose adjustment were determined and evaluated for appropriate dosing according to eGFR. A total of 388 patients with concomitant heart failure and renal dysfunction were included in the study. The total number of prescribed medications was 2808 and 48.3% (1357 medications) required renal dose adjustment. Of the 1357 medications, 12.6% (171 medications) were found to be inappropriately prescribed according to eGFR. The most common inappropriately prescribed medications were famotidine, metformin, perindopril, and ramipril. A significant portion of medications used in heart failure requires dose adjustment. Our results showed that in a typical cohort of patients with heart failure, many drugs are prescribed at inappropriately high doses according to creatinine clearance. Awareness should be increased among physicians caring for patients with heart failure to prevent adverse events related to medications.
Estimating renal function in children: a new GFR-model based on serum cystatin C and body cell mass.
Andersen, Trine Borup
2012-07-01
This PhD thesis is based on four individual studies including 131 children aged 2-14 years with nephro-urologic disorders. The majority (72%) of children had a normal renal function (GFR > 82 ml/min/1.73 square metres), and only 8% had a renal function GFR model based on a novel theory of body cell mass (BCM) and cystatin C (CysC); 2) to investigate the diagnostic performance in comparison to other models as well as serum CysC and creatinine; 3) to validate the new models precision and validity. The model´s diagnostic performance was investigated in study I as the ability to detect changes in renal function (total day-to-day variation), and in study IV as the ability to discriminate between normal and reduced function. The model´s precision and validity were indirectly evaluated in study II and III, and in study I accuracy was estimated by comparison to reference GFR. Several prediction models based on CysC or a combination of CysC and serum creatinine have been developed for predicting GFR in children. Despite these efforts to improve GFR estimates, no alternative to exogenous methods has been found and the Schwartz´s formula based on height, creatinine and an empirically derived constant is still recommended for GFR estimation in children. However, the inclusion of BCM as a possible variable in a CysC-based prediction model has not yet been explored. As CysC is produced at a constant rate from all nucleated cells we hypothesize that including BCM in a new prediction model will increase accuracy of the GFR estimate. Study I aimed at deriving the new GFR-prediction model based on the novel theory of CysC and BCM and comparing the performance to previously published models. The BCM-model took the form GFR (mL/min) = 10.2 × (BCM/CysC)E 0.40 × (height × body surface area/Crea)E 0.65. The model predicted 99% within ± 30% of reference GFR, and 67% within ±10%. This was higher than any other model. The present model also had the highest R E2 and the narrowest 95
Relaxation approximations and bounded variation estimates for some partial differential equations
Directory of Open Access Journals (Sweden)
Francisco Caicedo
2002-02-01
Full Text Available In this paper, we introduce a new technique for studying solutions of bounded variation for some conservation laws of first order partial differential equations and for some degenerate parabolic equations in multi-dimensional space. The connection between these two types of equations is the vanishing relaxation method.
Directory of Open Access Journals (Sweden)
Rajagopalan P
2016-09-01
Full Text Available Prashanth Rajagopalan,1 Georgi Abraham,2 Yuvaram NV Reddy,2 Ravivarman Lakshmanasami,1 ML Prakash,1 Yogesh NV Reddy2 1Department of General Medicine, Mahatma Gandhi Medical College and Research Institute, Puducherry, 2Department of Nephrology, Madras Medical Mission Hospital, Chennai, India Abstract: This population-based prospective study was undertaken in Mahatma Gandhi Medical College to estimate the renal function in young healthy Indian adults. A young healthy heterogeneous Indian cohort comprising 978 individuals, predominantly medical students, was assessed by a detailed questionnaire, and variables such as height, weight, body mass index (BMI, birth weight, and blood pressure were documented. Laboratory investigations included serum creatinine, serum cystatin C, blood sugar, urine protein, and imaging of the kidneys with ultrasound. The mean age of the cohort was 25±6 years, comprising 672 males and 306 females. The estimated glomerular filtration rates (eGFRs by the Cockcroft–Gault formula for BMI <18.5 kg/m2, 18.5–24.99 kg/m2, 25–29.99 kg/m2, and ≥30 kg/m2 were 71.29±10.45 mL/min, 86.38±13.46 mL/min, 98.88±15.29 mL/min, and 109.13±21.57 mL/min, respectively; the eGFRs using cystatin C for the four groups of BMI were 84.53±18.14 mL/min, 84.01±40.11 mL/min, 79.18±13.46 mL/min, and 77.30±10.90 mL/min, respectively. This study attempts to establish a normal range of serum creatinine and cystatin C values for the Indian population and shows that in young healthy Indian adults, eGFR and kidney volume vary by BMI and sex. Keywords: eGFR, birth weight, renal volume
A Regression Equation for the Estimation of Maximum Oxygen Uptake in Nepalese Adult Females
Chatterjee, Pinaki; Banerjee, Alok K; Das, Paulomi; Debnath, Parimal
2010-01-01
Purpose Validity of the 20-meter multi stage shuttle run test (20-m MST) has not been studied in Nepalese population. The purpose of this study was to validate the applicability of the 20-m MST in Nepalese adult females. Methods Forty female college students (age range, 20.42 ~24.75 years) from different colleges of Nepal were recruited for the study. Direct estimation of VO2 max comprised treadmill exercise followed by expired gas analysis by scholander micro-gas analyzer whereas VO2 max was indirectly predicted by the 20-m MST. Results The difference between the mean (±SD) VO2 max values of direct measurement (VO2 max = 32.78 +/-2.88 ml/kg/min) and the 20-m MST (SPVO2 max = 32.53 + /-3.36 ml/kg/min) was statistically insignificant (P>0.1). Highly significant correlation (r=0.94, PVO2 max. Limits of agreement analysis also suggest that the 20-m MST can be applied for the studied population. Conclusion The results of limits of agreement analysis suggest that the application of the present form of the 20-m MST may be justified in the studied population. However, for better prediction of VO2 max, a new equation has been computed based on the present data to be used for female college students of Nepal. PMID:22375191
Urrutia, Jackie D.; Tampis, Razzcelle L.; Mercado, Joseph; Baygan, Aaron Vito M.; Baccay, Edcon B.
2016-02-01
The objective of this research is to formulate a mathematical model for the Philippines' Real Gross Domestic Product (Real GDP). The following factors are considered: Consumers' Spending (x1), Government's Spending (x2), Capital Formation (x3) and Imports (x4) as the Independent Variables that can actually influence in the Real GDP in the Philippines (y). The researchers used a Normal Estimation Equation using Matrices to create the model for Real GDP and used α = 0.01.The researchers analyzed quarterly data from 1990 to 2013. The data were acquired from the National Statistical Coordination Board (NSCB) resulting to a total of 96 observations for each variable. The data have undergone a logarithmic transformation particularly the Dependent Variable (y) to satisfy all the assumptions of the Multiple Linear Regression Analysis. The mathematical model for Real GDP was formulated using Matrices through MATLAB. Based on the results, only three of the Independent Variables are significant to the Dependent Variable namely: Consumers' Spending (x1), Capital Formation (x3) and Imports (x4), hence, can actually predict Real GDP (y). The regression analysis displays that 98.7% (coefficient of determination) of the Independent Variables can actually predict the Dependent Variable. With 97.6% of the result in Paired T-Test, the Predicted Values obtained from the model showed no significant difference from the Actual Values of Real GDP. This research will be essential in appraising the forthcoming changes to aid the Government in implementing policies for the development of the economy.
Rajagopalan, Prashanth; Abraham, Georgi; Reddy, Yuvaram Nv; Lakshmanasami, Ravivarman; Prakash, M L; Reddy, Yogesh Nv
2016-01-01
This population-based prospective study was undertaken in Mahatma Gandhi Medical College to estimate the renal function in young healthy Indian adults. A young healthy heterogeneous Indian cohort comprising 978 individuals, predominantly medical students, was assessed by a detailed questionnaire, and variables such as height, weight, body mass index (BMI), birth weight, and blood pressure were documented. Laboratory investigations included serum creatinine, serum cystatin C, blood sugar, urine protein, and imaging of the kidneys with ultrasound. The mean age of the cohort was 25±6 years, comprising 672 males and 306 females. The estimated glomerular filtration rates (eGFRs) by the Cockcroft-Gault formula for BMI <18.5 kg/m(2), 18.5-24.99 kg/m(2), 25-29.99 kg/m(2), and ≥30 kg/m(2) were 71.29±10.45 mL/min, 86.38±13.46 mL/min, 98.88±15.29 mL/min, and 109.13±21.57 mL/min, respectively; the eGFRs using cystatin C for the four groups of BMI were 84.53±18.14 mL/min, 84.01±40.11 mL/min, 79.18±13.46 mL/min, and 77.30±10.90 mL/min, respectively. This study attempts to establish a normal range of serum creatinine and cystatin C values for the Indian population and shows that in young healthy Indian adults, eGFR and kidney volume vary by BMI and sex.
Estimation of Energy Equation Correlate of CMEs with X-Ray Flares during Solar Cycle 23rd
Shaltout, Mosalam; Shaltout, Mosalam; Ramy Mawad, Rr.
. The aim of this paper is estimating the energy equation of CMEs with associated X-ray flares. In addition, we studied, when and where X-ray flares can eject CMEs? We are used CMEs data which observed from SOHO/LASCO, during the full solar cycle 23rd (1996- 2006), we have 12433 events. Also we are used the X-Ray flares data observed by Geostationary Operational Environmental Satellite (GEOS), during the same interval (1996-2006) in the 1-8 Ao GEOS Channel, it is recorded 22688 X-ray flare events. We had estimated energy equation between CMEs and associated X-ray flares during solar cycle 23rd (1996-2006). It is found the energy equation between them is polynomial series with correlation coefficient 92%. The characteristics of the CMEs and associated X-ray flares have been studied.
Pinto, Andressa S; Chedid, Marcio F; Guerra, Léa T; Álvares-DA-Silva, Mario R; Araújo, Alexandre de; Guimarães, Luciano S; Leipnitz, Ian; Chedid, Aljamir D; Kruel, Cleber R P; Grezzana-Filho, Tomaz J M; Kruel, Cleber D P
2016-01-01
Reliable measurement of basal energy expenditure (BEE) in liver transplant (LT) recipients is necessary for adapting energy requirements, improving nutritional status and preventing weight gain. Indirect calorimetry (IC) is the gold standard for measuring BEE. However, BEE may be estimated through alternative methods, including electrical bioimpedance (BI), Harris-Benedict Equation (HBE), and Mifflin-St. Jeor Equation (MSJ) that carry easier applicability and lower cost. To determine which of the three alternative methods for BEE estimation (HBE, BI and MSJ) would provide most reliable BEE estimation in LT recipients. Prospective cross-sectional study including dyslipidemic LT recipients in follow-up at a 735-bed tertiary referral university hospital. Comparisons of BEE measured through IC to BEE estimated through each of the three alternative methods (HBE, BI and MSJ) were performed using Bland-Altman method and Wilcoxon Rank Sum test. Forty-five patients were included, aged 58±10 years. BEE measured using IC was 1664±319 kcal for males, and 1409±221 kcal for females. Average difference between BEE measured by IC (1534±300 kcal) and BI (1584±377 kcal) was +50 kcal (p=0.0384). Average difference between the BEE measured using IC (1534±300 kcal) and MSJ (1479.6±375 kcal) was -55 kcal (p=0.16). Average difference between BEE values measured by IC (1534±300 kcal) and HBE (1521±283 kcal) was -13 kcal (p=0.326). Difference between BEE estimated through IC and HBE was less than 100 kcal for 39 of all 43patients. Among the three alternative methods, HBE was the most reliable for estimating BEE in LT recipients. Estimativa confiável do metabolismo basal em pacientes transplantados de fígado é necessária para adaptar os requerimentos energéticos, melhorar o estado nutricional e prevenir ganho de peso. Calorimetria indireta (CI) é o padrão-ouro para a medição do metabolismo basal. No entanto, ele pode ser estimado utilizando-se métodos alternativos
Gugushvili, S.; Spreij, P.
2016-01-01
We consider the problem of non-parametric estimation of the deterministic dispersion coefficient of a linear stochastic differential equation based on discrete time observations on its solution. We take a Bayesian approach to the problem and under suitable regularity assumptions derive the posteror
Institute of Scientific and Technical Information of China (English)
蒋永生; 田范基
2012-01-01
The purpose of this paper is to give an elementary and simple proof for the Schauder estimates for Kohn Laplace equations in the Heisenberg group Hn.%研究了Heisenberg群Hn中的Kohn-Laplace方程,用一个简单的方法证明了该方程的Schauder估计.
Strong Consistency of Generalized Estimation Equation Root%广义估计方程根的强相合性
Institute of Scientific and Technical Information of China (English)
王健发; 陈淑兰; 闫莉
2011-01-01
The paper studies strong consistency of generalized estimation equation root.Under the generalized estimating equation having correct assumption,when the number of subjects goes to infinity and the residuals form a martingale difference sequence,the paper uses martingale Benstein Inequality to prove strong consistency of the generalized estimation equation root.At the same time when the number of subjects is one,and the number of observations on the subject goes to infinity,and the residuals form a martingale difference sequence,the paper proves strong consistency of generalized estimation equation root.%在广义估计方程有正确假定,当个体数目趋于无穷而残差为鞅差序列时,用鞅伯恩斯坦不等式证明广义估计方程根的强相合性,同时在个体数目为1而重复观测次数趋于无穷且残差为鞅差序列时,也证明了广义估计方程根的强相合性.
Dattner, I.; Klaassen, C.A.J.
2015-01-01
Many processes in biology, chemistry, physics, medicine, and engineering are modeled by a system of differential equations. Such a system is usually characterized via unknown parameters and estimating their ‘true’ value is thus required. In this paper we focus on the quite common systems for which t
Directory of Open Access Journals (Sweden)
Haitao Che
2011-01-01
Full Text Available We investigate a H1-Galerkin mixed finite element method for nonlinear viscoelasticity equations based on H1-Galerkin method and expanded mixed element method. The existence and uniqueness of solutions to the numerical scheme are proved. A priori error estimation is derived for the unknown function, the gradient function, and the flux.
Pan, Feifei; Nieswiadomy, Michael
2016-11-01
Soil moisture in snow-dominated regions has many important applications including evapotranspiration estimation, flood forecasting, water resource and ecosystem services management, weather prediction and climate modeling, and quantification of denudation processes. A simple and robust empirical approach to estimate root-zone soil moisture in snow-dominated regions using a soil moisture diagnostic equation that incorporates snowfall and snowmelt processes is suggested and tested. A five-water-year dataset (10/1/2010-9/30/2015) of daily precipitation, air temperature, snow water equivalent and soil moistures at three depths (i.e., 5 cm, 20 cm, and 50 cm) at each of 12 Snow Telemetry (SNOTEL) sites across Utah (37.583°N-41.883°N, 110.183°W-112.9°W), is applied to test the proposed method. The first three water years are designated as the parameter-estimation period (PEP) and the last two water years are chosen as the model-testing period (MTP). Applying the estimated soil moisture loss function parameters and other empirical parameters in the soil moisture diagnostic equation in the PEP, soil moistures in three soil columns (0-5 cm, 0-20 cm, and 0-50 cm) are estimated in the MTP. The relatively accurate soil moisture estimations compared to the observations at 12 SNOTEL sites (RMSE ⩽ 6.23 (%V/V), average RMSE = 4.28 (%V/V), correlation coefficient ⩾0.75, average correlation coefficient =0.89, the Nash-Sutcliffe efficient coefficient Ec ⩾ 0.24, average Ec = 0.72) indicate that the soil moisture diagnostic equation is capable of accurately estimating soil moisture in snow-dominated regions after the snowfall and snowmelt processes are included in the soil moisture diagnostic equation.
Zhang, Yiwei; Xu, Zhiyuan; Shen, Xiaotong; Pan, Wei
2014-08-01
There is an increasing need to develop and apply powerful statistical tests to detect multiple traits-single locus associations, as arising from neuroimaging genetics and other studies. For example, in the Alzheimer's Disease Neuroimaging Initiative (ADNI), in addition to genome-wide single nucleotide polymorphisms (SNPs), thousands of neuroimaging and neuropsychological phenotypes as intermediate phenotypes for Alzheimer's disease, have been collected. Although some classic methods like MANOVA and newly proposed methods may be applied, they have their own limitations. For example, MANOVA cannot be applied to binary and other discrete traits. In addition, the relationships among these methods are not well understood. Importantly, since these tests are not data adaptive, depending on the unknown association patterns among multiple traits and between multiple traits and a locus, these tests may or may not be powerful. In this paper we propose a class of data-adaptive weights and the corresponding weighted tests in the general framework of generalized estimation equations (GEE). A highly adaptive test is proposed to select the most powerful one from this class of the weighted tests so that it can maintain high power across a wide range of situations. Our proposed tests are applicable to various types of traits with or without covariates. Importantly, we also analytically show relationships among some existing and our proposed tests, indicating that many existing tests are special cases of our proposed tests. Extensive simulation studies were conducted to compare and contrast the power properties of various existing and our new methods. Finally, we applied the methods to an ADNI dataset to illustrate the performance of the methods. We conclude with the recommendation for the use of the GEE-based Score test and our proposed adaptive test for their high and complementary performance. Copyright © 2014 Elsevier Inc. All rights reserved.
A Numerical Method for the Estimation of Distributed Hydraulic Conductivity Using Richards Equation
Cockett, R.; Haber, E.
2013-12-01
Characterizing groundwater flow in the vadose zone has many important and practical applications in near surface hydrogeology. The spatial estimation of the hydraulic conductivity function, which is the regulator of unsaturated groundwater flow, is an critical step in any hydrogeologic site characterization. However, this estimation is difficult and simplifications are consistently used to avert these conceptual and computational difficulties. Comprehensive time-lapse data of in situ saturations, or proxies of saturation from geophysical methods, are increasingly available. Using these large data sets appropriately, and maximizing the utility of the data to recover estimates of heterogeneous hydraulic conductivity, requires innovative numerical methods. This inverse problem has been approached in many different ways in the literature from stochastic methods to various gradient based methods. However, the way in which the computational complexity of the inverse method scales becomes important as problem size increases; as computational memory and time often become the bottleneck of solving the inverse problem when the problem is solved for heterogeneous hydraulic conductivity in two- and particularly in three-dimensions. For the inverse problem involving Richards equation, some version of a Gauss-Newton method (e.g. Levenberg-Marquardt) with a direct calculation of the sensitivity matrix is commonly used. However, while these approaches allow to deal with moderate scale problems they have one major drawback: the sensitivity matrix is a large dense matrix and its computation requires dense linear algebra and, for large scale problems, a non-trivial amount of storage. Furthermore, previous work use either numerical or automatic differentiation in order to compute the sensitivity matrix and this can generate inaccuracies in its computation and tarry convergence of the optimization algorithm. We suggest a modern numerical method that allows for the solution of the
Deng, Fang; Finer, Gal; Haymond, Shannon; Brooks, Ellen; Langman, Craig B
2015-03-01
Estimating glomerular filtration rate (eGFR) has become popular in clinical medicine as an alternative to measured GFR (mGFR), but there are few studies comparing them in clinical practice. We determined mGFR by iohexol clearance in 81 consecutive children in routine practice and calculated eGFR from 14 standard equations using serum creatinine, cystatin C, and urea nitrogen that were collected at the time of the mGFR procedure. Nonparametric Wilcoxon test, Spearman correlation, Bland-Altman analysis, bias (median difference), and accuracy (P15, P30) were used to compare mGFR with eGFR. For the entire study group, the mGFR was 77.9 ± 38.8 mL/min/1.73 m(2). Eight of the 14 estimating equations demonstrated values without a significant difference from the mGFR value and demonstrated a lower bias in Bland-Altman analysis. Three of these 8 equations based on a combination of creatinine and cystatin C (Schwartz et al. New equations to estimate GFR in children with CKD. J Am Soc Nephrol 2009;20:629-37; Schwartz et al. Improved equations estimating GFR in children with chronic kidney disease using an immunonephelometric determination of cystatin C. Kidney Int 2012;82:445-53; Chehade et al. New combined serum creatinine and cystatin C quadratic formula for GFR assessment in children. Clin J Am Soc Nephrol 2014;9:54-63) had the highest accuracy with approximately 60% of P15 and 80% of P30. In 10 patients with a single kidney, 7 with kidney transplant, and 11 additional children with short stature, values of the 3 equations had low bias and no significant difference when compared with mGFR. In conclusion, the 3 equations that used cystatin C, creatinine, and growth parameters performed in a superior manner over univariate equations based on either creatinine or cystatin C and also had good applicability in specific pediatric patients with single kidneys, those with a kidney transplant, and short stature. Thus, we suggest that eGFR calculations in pediatric clinical practice
New Equation for Estimating Outdoor Thermal Comfort in Humid-Tropical Environment.
Directory of Open Access Journals (Sweden)
S Sangkertadi
2014-10-01
Full Text Available This paper presents the results of research focusing on thermal comfort at outdoor spaces in humid tropical climate. The study was conducted in the city of Manado, Indonesia inthe years 2011 and 2012, by way of field-experimentation and measurements of microclimate.From the results of measurements and questionnaires, it was carried out development of regression equations. Through statistical analysis it has been generated three thermal comfort equations for outdoor, which each for normal walking, briskwalking, and sitting with doing a moderate activity. Equations are functions of Ta(air temperature, Tg(globe temperature, v(wind velocity, RH(Relative humidity and Adu(body surface area. The output of the equations is scale of thermal comfort level referring to PMV (Predicted Mean Vote, where 0 is comfortable or neutral, +3 is very hot, -2 is cold, .etc. The equations are uniquely for the people wearing tropical clothing type (about 0.5 to 0.7 clo. The validation of the equations was done through comparison with other equations that originated from the studies of non-tropical humid climates. Simulations using the equations were also be done in order to know effect of micro climate on outdoor thermal comfort.Keywords: thermal comfort, tropical-humid, micro-climate, Manado
DEFF Research Database (Denmark)
Ditlevsen, Susanne; Samson, Adeline
2016-01-01
Dynamics of the membrane potential in a single neuron can be studied by estimating biophysical parameters from intracellular recordings. Diffusion processes, given as continuous solutions to stochastic differential equations, are widely applied as models for the neuronal membrane potential...... evolution. One-dimensional models are the stochastic integrate-and-fire neuronal diffusion models. Biophysical neuronal models take into account the dynamics of ion channels or synaptic activity, leading to multidimensional diffusion models. Since only the membrane potential can be measured......, this complicates the statistical inference and parameter estimation from these partially observed detailed models. This paper reviews parameter estimation techniques from intracellular recordings in these diffusion models....
Stroberg, Wylie; Schnell, Santiago
2016-12-01
The conditions under which the Michaelis-Menten equation accurately captures the steady-state kinetics of a simple enzyme-catalyzed reaction is contrasted with the conditions under which the same equation can be used to estimate parameters, KM and V, from progress curve data. Validity of the underlying assumptions leading to the Michaelis-Menten equation are shown to be necessary, but not sufficient to guarantee accurate estimation of KM and V. Detailed error analysis and numerical "experiments" show the required experimental conditions for the independent estimation of both KM and V from progress curves. A timescale, tQ, measuring the portion of the time course over which the progress curve exhibits substantial curvature provides a novel criterion for accurate estimation of KM and V from a progress curve experiment. It is found that, if the initial substrate concentration is of the same order of magnitude as KM, the estimated values of the KM and V will correspond to their true values calculated from the microscopic rate constants of the corresponding mass-action system, only so long as the initial enzyme concentration is less than KM. Copyright © 2016 Elsevier B.V. All rights reserved.
Error Estimate for a Fully Discrete Spectral Scheme for Korteweg-de Vries-Kawahara Equation
Koley, U
2011-01-01
We are concerned with the convergence of spectral method for the numerical solution of the initial-boundary value problem associated to the Korteweg-de Vries-Kawahara equation (in short Kawahara equation), which is a transport equation perturbed by dispersive terms of 3rd and 5th order. This equation appears in several fluid dynamics problems. It describes the evolution of small but finite amplitude long waves in various problems in fluid dynamics. These equations are discretized in space by the standard Fourier- Galerkin spectral method and in time by the explicit leap-frog scheme. For the resulting fully discrete, conditionally stable scheme we prove an L2-error bound of spectral accuracy in space and of second-order accuracy in time.
Directory of Open Access Journals (Sweden)
Chittawatanarat K
2012-01-01
Full Text Available Kaweesak Chittawatanarat1,2, Sakda Pruenglampoo3, Vibul Trakulhoon4, Winai Ungpinitpong5, Jayanton Patumanond21Department of Surgery, Faculty of Medicine, 2Clinical Epidemiology Unit, 3Research Institute for Health Sciences, Chiang Mai University, Chiang Mai, Thailand; 4Department of Surgery, Bhumibol Adulyadej Hospital, Bangkok, Thailand; 5Surgical Unit, Surin Hospital, Surin, ThailandBackground: Many medical procedures routinely use body weight as a parameter for calculation. However, these measurements are not always available. In addition, the commonly used visual estimation has had high error rates. Therefore, the aim of this study was to develop a predictive equation for body weight using body circumferences.Methods: A prospective study was performed in healthy volunteers. Body weight, height, and eight circumferential level parameters including neck, arm, chest, waist, umbilical level, hip, thigh, and calf were recorded. Linear regression equations were developed in a modeling sample group divided by sex and age (younger <60 years and older ≥60 years. Original regression equations were modified to simple equations by coefficients and intercepts adjustment. These equations were tested in an independent validation sample.Results: A total of 2000 volunteers were included in this study. These were randomly separated into two groups (1000 in each modeling and validation group. Equations using height and one covariate circumference were developed. After the covariate selection processes, covariate circumference of chest, waist, umbilical level, and hip were selected for single covariate equations (Sco. To reduce the body somatotype difference, the combination covariate circumferences were created by summation between the chest and one torso circumference of waist, umbilical level, or hip and used in the equation development as a combination covariate equation (Cco. Of these equations, Cco had significantly higher 10% threshold error tolerance
Schmidt, Rita; Webb, Andrew
2016-01-01
Electrical Properties Tomography (EPT) using MRI is a technique that has been developed to provide a new contrast mechanism for in vivo imaging. Currently the most common method relies on the solution of the homogeneous Helmholtz equation, which has limitations in accurate estimation at tissue interfaces. A new method proposed in this work combines a Maxwell's integral equation representation of the problem, and the use of high permittivity materials (HPM) to control the RF field, in order to reconstruct the electrical properties image. The magnetic field is represented by an integral equation considering each point as a contrast source. This equation can be solved in an inverse method. In this study we use a reference simulation or scout scan of a uniform phantom to provide an initial estimate for the inverse solution, which allows the estimation of the complex permittivity within a single iteration. Incorporating two setups with and without the HPM improves the reconstructed result, especially with respect to the very low electric field in the center of the sample. Electromagnetic simulations of the brain were performed at 3 T to generate the B1+ field maps and reconstruct the electric properties images. The standard deviations of the relative permittivity and conductivity were within 14% and 18%, respectively for a volume consisting of white matter, gray matter and cerebellum.
Schmidt, Rita; Webb, Andrew
2016-01-01
Electrical Properties Tomography (EPT) using MRI is a technique that has been developed to provide a new contrast mechanism for in vivo imaging. Currently the most common method relies on the solution of the homogeneous Helmholtz equation, which has limitations in accurate estimation at tissue interfaces. A new method proposed in this work combines a Maxwell's integral equation representation of the problem, and the use of high permittivity materials (HPM) to control the RF field, in order to reconstruct the electrical properties image. The magnetic field is represented by an integral equation considering each point as a contrast source. This equation can be solved in an inverse method. In this study we use a reference simulation or scout scan of a uniform phantom to provide an initial estimate for the inverse solution, which allows the estimation of the complex permittivity within a single iteration. Incorporating two setups with and without the HPM improves the reconstructed result, especially with respect to the very low electric field in the center of the sample. Electromagnetic simulations of the brain were performed at 3T to generate the B1(+) field maps and reconstruct the electric properties images. The standard deviations of the relative permittivity and conductivity were within 14% and 18%, respectively for a volume consisting of white matter, gray matter and cerebellum.
Schymanski, S. J.; Or, D.
2016-12-01
The Penman-Monteith (PM) equation is considered the most advanced physically based approach to estimating transpiration rates from plants considering stomatal conductance and atmospheric drivers. The PM has been widely evaluated at the canopy scale, where aerodynamic and canopy resistances are difficult to estimate directly, leading to various empirical adaptations when scaling from leaf to canopy. Here we evaluated the PM equation directly at the leaf scale, using a detailed leaf energy balance model and direct measurements in an insulated mini-wind tunnel using artificial leaves with pre-defined "stomatal" conductance. Experimental results were consistent with the detailed leaf energy balance model, but expressed systematic deviations from PM-predicted fluxes, which pointed to fundamental problems with the PM equation. Detailed analysis of Monteith's (1965) derivations and subsequent amendments revealed two errors in incorporating stomata and the two-sided exchange of sensible heat. A corrected analytical expression for leaf temperature, latent and sensible heat fluxes is presented and compared with the original PM equation indicating a major improvement in reproducing experimental results at the leaf scale. The errors in the original PM equation and discrepancies with experimental results at the leaf scale propagate into inaccurate sensitivities of transpiration and sensible heat fluxes to changes in atmospheric drivers, such as those associated with climate change (despite reasonable present day performance after calibration). The new formulation rectifies some of the shortcomings of the PM equation and provides a more robust starting point for estimating trends in canopy water demand under changing climate, as illustrated in this presentation.
Directory of Open Access Journals (Sweden)
Muhammed Çetin
2015-01-01
Full Text Available An approximation method based on Lucas polynomials is presented for the solution of the system of high-order linear differential equations with variable coefficients under the mixed conditions. This method transforms the system of ordinary differential equations (ODEs to the linear algebraic equations system by expanding the approximate solutions in terms of the Lucas polynomials with unknown coefficients and by using the matrix operations and collocation points. In addition, the error analysis based on residual function is developed for present method. To demonstrate the efficiency and accuracy of the method, numerical examples are given with the help of computer programmes written in Maple and Matlab.
Energy Technology Data Exchange (ETDEWEB)
Lee, Yongjin; Shin, Moon Sam [School of Chemical and Biological Engineering and Institute of Chemical Processes, Seoul National University, Seoul 151-744 (Korea, Republic of); Kim, Hwayong [School of Chemical and Biological Engineering and Institute of Chemical Processes, Seoul National University, Seoul 151-744 (Korea, Republic of)], E-mail: hwayongk@snu.ac.kr
2008-11-15
We apply the crossover lattice equation of state (xLF EOS) [M.S. Shin, Y. Lee, H. Kim, J. Chem. Thermodyn. 40 (2007) 174-179] to the calculations of thermodynamic 2nd-order derivative properties (isochoric heat capacity, isobaric heat capacity, isothermal compressibility, thermal expansion coefficient, Joule-Thompson coefficient, and sound speed). This equation of state is used to calculate the same properties of pure systems (carbon dioxide, normal alkanes from methane to propane). We show that, over a wide range of states, the equation of state yields properties with better accuracy than the lattice equation of state (LF EOS), and near the critical region, represents singular behavior well.
Directory of Open Access Journals (Sweden)
Per Lunde
2016-07-01
Full Text Available Acoustic methods used in fish abundance estimation constitute a key part of the analytic assessment that makes the basis for abundance estimation of marine resources. The methods rely on power-budget equations and calibrated systems. Different formulations of power-budget equations and calibration factors have been proposed for use in scientific echo sounder and sonar systems. There are unresolved questions and apparent inconsistencies in prior literature related to this field. A generic (instrument independent and unifying theory is presented that attempts to explain the different power-budget and calibration factor formulations proposed and used in prior literature, and how these are mutually related. Deviations and apparent inconsistencies in this literature appear to be explained and corrected. This also includes different (instrument specific formulations employed in important modern scientific echo sounder systems, and their relationship to the generic theory of abundance estimation. Prior literature is extended to provide more complete power-budget equations for fish abundance estimation and species identification, by accounting for echo integration, electrical termination, and the full range of electrical and acoustical echo sounder parameters. The expressions provide a consistent theoretical basis for improved understanding of conventional methods and instruments used today, also enabling improved sensitivity and error analyses, and correction possibilities.
Syrakos, Alexandros
2015-01-01
A methodology is proposed for the calculation of the truncation error of finite volume discretisations of the incompressible Navier-Stokes equations on colocated grids. The truncation error is estimated by restricting the solution obtained on a given grid to a coarser grid and calculating the image of the discrete Navier-Stokes operator of the coarse grid on the restricted velocity and pressure field. The proposed methodology is not a new concept but its application to colocated finite volume discretisations of the incompressible Navier-Stokes equations is made possible by the introduction of a variant of the momentum interpolation technique for mass fluxes where the pressure-part of the mass fluxes is not dependent on the coefficients of the linearised momentum equations. The theory presented is supported by a number of numerical experiments. The methodology is developed for two-dimensional flows, but extension to three-dimensional cases should not pose problems.
Directory of Open Access Journals (Sweden)
Mini Joseph
2017-01-01
Full Text Available Background: The accuracy of existing predictive equations to determine the resting energy expenditure (REE of professional weightlifters remains scarcely studied. Our study aimed at assessing the REE of male Asian Indian weightlifters with indirect calorimetry and to compare the measured REE (mREE with published equations. A new equation using potential anthropometric variables to predict REE was also evaluated. Materials and Methods: REE was measured on 30 male professional weightlifters aged between 17 and 28 years using indirect calorimetry and compared with the eight formulas predicted by Harris–Benedicts, Mifflin-St. Jeor, FAO/WHO/UNU, ICMR, Cunninghams, Owen, Katch-McArdle, and Nelson. Pearson correlation coefficient, intraclass correlation coefficient, and multiple linear regression analysis were carried out to study the agreement between the different methods, association with anthropometric variables, and to formulate a new prediction equation for this population. Results: Pearson correlation coefficients between mREE and the anthropometric variables showed positive significance with suprailiac skinfold thickness, lean body mass (LBM, waist circumference, hip circumference, bone mineral mass, and body mass. All eight predictive equations underestimated the REE of the weightlifters when compared with the mREE. The highest mean difference was 636 kcal/day (Owen, 1986 and the lowest difference was 375 kcal/day (Cunninghams, 1980. Multiple linear regression done stepwise showed that LBM was the only significant determinant of REE in this group of sportspersons. A new equation using LBM as the independent variable for calculating REE was computed. REE for weightlifters = −164.065 + 0.039 (LBM (confidence interval −1122.984, 794.854]. This new equation reduced the mean difference with mREE by 2.36 + 369.15 kcal/day (standard error = 67.40. Conclusion: The significant finding of this study was that all the prediction equations
Directory of Open Access Journals (Sweden)
M. I. Kogan
2011-01-01
Full Text Available There is an increase in the number of patients with renal cell carcinoma (RCC every year. At the same time radical nephrectomy (RN remains the standard treatment of renal malignancies and the most common surgical procedure for this pathology. A considerable number of patients with kidney cancer have diminished renal function that worsens after removal of functioning kidney tissue together with a tumor. This promotes retained low overall survival rates in patients with RCC, by improving cancer-specific survival. Renal function was studied in 48 patients with RCC prior to and 1 year after RN. In all the patients, glomerular filtration rate (GFR was estimated using the Cockroft-Gault equation with and without protein load. Renal parenchyma volume was calculated by spiral computed tomography. Patients aged over 60 years had decreased baseline renal function as compared to those aged under 60 years (GFR 77.4 versus 103.6 ml/min/1.73 m2. The postoperative reduction in female renal function was more pronounced (GFR, 84.92 versus 92.54 ml/min/1.73 m2. Patients with metastatic RCC had lower baseline renal function and its significant postoperative loss than those with the non-metastatic forms of a tumor. A load test showed a substantially decreased renal reserve in patients with RCC.
Kramer, Sean; Bollt, Erik M
2013-09-01
Given multiple images that describe chaotic reaction-diffusion dynamics, parameters of a partial differential equation (PDE) model are estimated using autosynchronization, where parameters are controlled by synchronization of the model to the observed data. A two-component system of predator-prey reaction-diffusion PDEs is used with spatially dependent parameters to benchmark the methods described. Applications to modeling the ecological habitat of marine plankton blooms by nonlinear data assimilation through remote sensing are discussed.
Directory of Open Access Journals (Sweden)
Hyun Young Lee
2010-01-01
Full Text Available We analyze discontinuous Galerkin methods with penalty terms, namely, symmetric interior penalty Galerkin methods, to solve nonlinear Sobolev equations. We construct finite element spaces on which we develop fully discrete approximations using extrapolated Crank-Nicolson method. We adopt an appropriate elliptic-type projection, which leads to optimal ℓ∞(L2 error estimates of discontinuous Galerkin approximations in both spatial direction and temporal direction.
DEFF Research Database (Denmark)
Ditlevsen, Susanne; Samson, Adeline
2016-01-01
evolution. One-dimensional models are the stochastic integrate-and-fire neuronal diffusion models. Biophysical neuronal models take into account the dynamics of ion channels or synaptic activity, leading to multidimensional diffusion models. Since only the membrane potential can be measured......Dynamics of the membrane potential in a single neuron can be studied by estimating biophysical parameters from intracellular recordings. Diffusion processes, given as continuous solutions to stochastic differential equations, are widely applied as models for the neuronal membrane potential...
RESIDUAL A POSTERIORI ERROR ESTIMATE OF A NEW TWO-LEVEL METHOD FOR STEADY NAVIER-STOKES EQUATIONS
Institute of Scientific and Technical Information of China (English)
Chunfeng REN; Yichen MA
2006-01-01
Residual-based a posteriori error estimate for conforming finite element solutions of incompressible Navier-Stokes equations, which is computed with a new two-level method that is different from Volker John, is derived. A posteriori error estimate contains additional terms in comparison to the estimate for the solution obtained by the standard finite element method. The importance of the additional terms in the error estimates is investigated by studying their asymptotic behavior. For optimal scaled meshes, these bounds are not of higher order than the convergence of discrete solution. The two-level method aims to solve the nonlinear problem on a coarse grid with less computational work,then to solve the linear problem on a fine grid, which is superior to the usual finite element method solving a similar nonlinear problem on the fine grid.
Directory of Open Access Journals (Sweden)
Georgiana Dunca
2016-01-01
Full Text Available The paper presents a new method for in site discharge estimation in pressured pipes. The method consists in using the water hammer equations solved with the method of characteristics with an unsteady friction factor model. The differential pressure head variation measured during a complete valve closure is used to derive the initial flow rate, similarly to the pressure-time (Gibson method. The method is validated with a numerical experiment, and tested with experimental laboratory measurements. The results show that the proposed method can reduce the discharge estimation error by 0.6% compared to the standard pressure-time (Gibson method for the flow rate investigation.
Smagin, V. V.
1997-04-01
We consider a weakly solvable parabolic problem in a separable Hilbert space. We seek approximations to the exact solution by projective and projective-difference methods. In this connection the discretization of the problem with respect to the spatial variables is carried out by the semidiscrete method of Galerkin, and with respect to time by the implicit method of Euler. In this paper we establish a coercive mean-square error estimate for the approximate solutions. We illustrate the effectiveness of these estimates with parabolic equations of second order with Dirichlet or Neumann boundary conditions in projective subspaces of finite element type.
Sierra Sanjurjo, Natalia; Montañes, Patricia; Sierra Matamoros, Fabio Alexander; Burin, Debora
2015-01-01
Spanish is the fourth most spoken language in the world, and the majority of Spanish speakers have a Latin American origin. Reading aloud infrequently accentuated words has been established as a National Adult Reading Test-like method to assess premorbid intelligence in Spanish. However, several versions have been proposed and validated with small and selected samples, in particular geographical conditions, and they seldom derive a formula for IQ estimation with the Wechsler Adult Intelligence Scale (WAIS) Full-Scale IQ (FSIQ). The objective of this study was to develop equations to estimate WAIS-Third Edition (WAIS-III) FSIQ from the Word Accentuation Test-Revised (WAT-R), demographic variables, and their combination within diverse Latin American samples. Two hundred and forty participants from Argentina and Colombia, selected according to age and years of education strata, were assessed with the WAT-R, the WAIS-III, and a structured questionnaire about demographic and medical information. A combined approach including place of birth, years of education, and WAT-R provided the best equation, explaining 76% of IQ variance. These equations could be useful for estimating premorbid IQ in patients with Latin American Spanish as their birth language.
Schwartz, George J; Schneider, Michael F; Maier, Paula S; Moxey-Mims, Marva; Dharnidharka, Vikas R; Warady, Bradley A; Furth, Susan L; Muñoz, Alvaro
2012-08-01
The Chronic Kidney Disease in Children study is a cohort of about 600 children with chronic kidney disease (CKD) in the United States and Canada. The independent variable for our observations was a measurement of glomerular filtration rate(GFR) by iohexol disappearance (iGFR) at the first two visits 1 year apart and during alternate years thereafter. In a previous report, we had developed GFR estimating equations utilizing serum creatinine, blood urea nitrogen, height, gender, and cystatin C measured by an immunoturbidimetric method; however, the correlation coefficient of cystatin C and GFR(0.69) was less robust than expected. Therefore, 495 samples were re-assayed using immunonephelometry. The reciprocal of immunonephelometric cystatin C was as well correlated with iGFR as was height/serum creatinine (both 0.88). We developed a new GFR estimating equation using a random 2/3 of 965 person-visits and applied it to the remaining 1/3 as a validation data set. In the validation dataset, the correlation of the estimated GFR with iGFR was 0.92 with high precision and no bias; 91 and 45% of eGFR values were within 30 and 10% of iGFR, respectively. This equation works well in children with CKD in a range of GFR from 15 to 75 ml/min per 1.73 m2. Further studies are needed to establish the applicability to children of normal stature and muscle mass, and higher GFR.
Head Loss Equations Estimate for Comercials Pipelines Conducting Wastewater from Poultry
Directory of Open Access Journals (Sweden)
José Antonio Rodrigues de Souza
2010-04-01
Full Text Available The objective of this work was to adjust equations to calculate continuous head loss in PVC, zinced steel, galvanized iron pipelines conducting wastewater from poultry with different concentrations of total solids. The head loss was determined by means of four piezometers, 4 m apart along the pipelines. The results indicated that the, for all pipelines, empirical equations adjusted with the methodologies of Duffy e Titchener and Hazen-Williams modified gave good results with coefficient of determination equivalent to 0.99, therefore, its application is recommended to design of projects with PVC pipelines.
An optimal variance estimate in stochastic homogenization of discrete elliptic equations
Gloria, Antoine; 10.1214/10-AOP571
2011-01-01
We consider a discrete elliptic equation on the $d$-dimensional lattice $\\mathbb{Z}^d$ with random coefficients $A$ of the simplest type: they are identically distributed and independent from edge to edge. On scales large w.r.t. the lattice spacing (i.e., unity), the solution operator is known to behave like the solution operator of a (continuous) elliptic equation with constant deterministic coefficients. This symmetric ``homogenized'' matrix $A_{\\mathrm {hom}}=a_{\\mathrm {hom}}\\operatorname {Id}$ is characterized by $\\xi\\cdot A_{\\mathrm {hom}}\\xi=\\langle(\\xi+\
DEFF Research Database (Denmark)
Andersen, Trine Borup; Jødal, Lars; Bøgsted, Martin
AIM: To derive an accurate prediction model for estimating glomerular filtration rate (GFR) in children based primarily on the endogenous renal function marker cystatin C (CysC) and body cell mass (BCM). THEORY: Cystatin C is produced at a constant rate in all cells of the body and is excreted...... by glomerular filtration followed by catabolization in the tubular cells. We hypothesized that production rate is proportional to body cell mass (BCM) and inferred GFR (mL/min) to be proportional to BCM/CysC. MATERIAL AND METHODS: GFR was determined with 51Cr-EDTA-clearance in 131 children (52 girls, 79 boys......) aged 2-14 years. GFR was 14-147 mL/min/1.73m2. BCM was estimated using bioimpedance spectroscopy. Log-transformed data on BCM/CysC, serum creatinine (SCr), body-surface-area (BSA), height×BSA/SCr, CysC, weight, sex, age, height, serum urea and albumin were considered possible explanatory variables...
DEFF Research Database (Denmark)
Andersen, Trine Borup; Jødal, Lars; Bøgsted, Martin
AIM: To derive an accurate prediction model for estimating glomerular filtration rate (GFR) in children based primarily on the endogenous renal function marker cystatin C (CysC) and body cell mass (BCM). THEORY: Cystatin C is produced at a constant rate in all cells of the body and is excreted...... by glomerular filtration followed by catabolization in the tubular cells. We hypothesized that production rate is proportional to body cell mass (BCM) and inferred GFR (mL/min) to be proportional to BCM/CysC. MATERIAL AND METHODS: GFR was determined with 51Cr-EDTA-clearance in 131 children (52 girls, 79 boys......) aged 2-14 years (mean 8.8 years). GFR was 14-147 mL/min/1.73m2 (mean 97 mL/min/1.73m2). BCM was estimated using bioimpedance spectroscopy (Xitron Hydra 4200). Log-transformed data on BCM/CysC, serum creatinine (SCr), body-surface-area (BSA), height x BSA/SCr, serum CysC, weight, sex, age, height, serum...
Yield stress of duplex stainless steel specimens estimated using a compound Hall–Petch equation
Directory of Open Access Journals (Sweden)
Noriaki Hirota, Fuxing Yin, Tsukasa Azuma and Tadanobu Inoue
2010-01-01
Full Text Available In this study, the 0.2% yield stress of duplex stainless steel was evaluated using a compound Hall–Petch equation. The compound Hall–Petch equation was derived from four types of duplex stainless steel, which contained 0.2–64.4 wt% δ-ferrite phase, had different chemical compositions and were annealed at different temperatures. Intragranular yield stress was measured with an ultra-microhardness tester and evaluated with the yield stress model proposed by Dao et al. Grain size, volume fraction and texture were monitored by electron backscattering diffraction measurement. The kγ constant in the compound equation for duplex stainless steel agrees well with that for γ-phase SUS316L steel in the temperature range of 1323–1473 K. The derived compound Hall–Petch equation predicts that the yield stress will be in good agreement with the experimental results for the Cr, Mn, Si, Ni and N solid-solution states. We find that the intragranular yield stress of the δ-phase of duplex stainless steel is rather sensitive to the chemical composition and annealing conditions, which is attributed to the size misfit parameter.
Maximum Likelihood Estimation of Nonlinear Structural Equation Models with Ignorable Missing Data
Lee, Sik-Yum; Song, Xin-Yuan; Lee, John C. K.
2003-01-01
The existing maximum likelihood theory and its computer software in structural equation modeling are established on the basis of linear relationships among latent variables with fully observed data. However, in social and behavioral sciences, nonlinear relationships among the latent variables are important for establishing more meaningful models…
Allometric equations for estimating biomass in naturally established Prosopis stands in Kenya
Muturi, G.M.; Kariuki, J.G.; Poorter, L.; Mohren, G.M.J.
2012-01-01
Forty five Prosopis stems of 2.5-18.0 cm diameter at breast height (DBH) were sampled at Nadapal along the Turkwel riverine forest for development of biomass and volume prediction equations for naturally established stands. Basal diameter (D30), DBH and heights were measured, felled trees and their
Evaluating equations estimating change in swine feed intake during heat and cold stress.
White, Robin R; Miller, Phillip S; Hanigan, Mark D
2015-11-01
The objectives of this study were to evaluate heat stress feed intake models for growing swine using a data set assembled from the literature and to develop a series of new equations modeling the influence of the thermal environment and interactions between the thermal environmental and other factors on feed intake. A literature survey was conducted to identify studies assessing intake responses to temperature. The resulting data set comprised 35 studies containing 120 comparisons to thermoneutral intake. Intake as a fraction of thermoneutral intake (FFI) was the primary response variable, where a value of 1 represented no change from thermoneutral intake. The FFI predicted by NRC and a recent model from a meta-analysis (Renaudeau et al.,) were compared to observed values. New parameters for the NRC equation (NRCmod) were derived, and a series of new equations incorporating duration of exposure (TD), temperature cycling (TC), and floor type (TH) were also derived. Root-mean-square prediction error (RMSPE) and concordance correlation coefficients were used to evaluate all models. The RMSPE for the NRC model was 23.6 with mean and slope bias accounting for 12.6% and 51.1% of prediction error, respectively. The TD, TC, and TH models had reduced RMSPE compared with NRC: 12.9 for TD, 12.6 for TC, and 12.9 for TS. Substantial improvements were also made by refitting parameters (NRCmod; RMSPE 13.0%). In NRCmod, TD, TC, and TH, random error was the predominant source, accounting for over 97% of prediction error. The Renaudeau et al. model was also evaluated. Renaudeau et al. had relatively low RMSPE (22.3) for intake but higher RMSPE for FFI (22.6) than NRC, NRCmod, TD, TC, or TH. Additional parameters were derived for the Renaudeau et al. equation to account for housing system and diet characteristics. This adjustment reduced RMSPE of predicting feed intake (16.0) and FFI (16.3) and reduced systematic bias in the equation. This evaluation of equations highlights the
Rosina, Kelli T C; Menna Barreto, Ana Paula M; Pontes, Karine S S; Martins, Cyro J M; Souza, Edison; Bregman, Rachel; Barreto Silva, Maria Inês; Klein, Márcia R S T
2017-05-01
Recent evidence suggests that vitamin D deficiency is associated with CVD, impaired kidney function and proteinuria. To date, no study has evaluated these associations in renal transplant recipients (RTR) adjusting for body adiposity assessed by a 'gold standard' method. This study aimed to evaluate the vitamin D status and its association with body adiposity, CVD risk factors, estimated glomerular filtration rate (eGFR) and proteinuria in RTR, living in Rio de Janeiro, Brazil (a low-latitude city (22°54'10"S)), taking into account body adiposity evaluated by dual-energy X-ray absorptiometry (DXA). This cross-sectional study included 195 RTR (114 men) aged 47·6 (sd 11·2) years. Nutritional evaluation included anthropometry and DXA. Risk factors for CVD were hypertension, diabetes mellitus, dyslipidaemia and the metabolic syndrome. eGFR was evaluated using the Chronic Kidney Disease Epidemiology Collaboration equation. Serum 25-hydroxyvitamin D (25(OH)D) concentration was used to define vitamin D status as follows: 10 % (n 19) had vitamin D deficiency (30 ng/ml). Percentage of body fat (DXA) was significantly associated with vitamin D deficiency independently of age, sex and eGFR. Lower 25(OH)D was associated with higher odds of the metabolic syndrome and dyslipidaemia after adjustment for age, sex and eGFR, but not after additional adjustment for body fat. Hypertension and diabetes were not related to 25(OH)D. Lower serum 25(OH)D was associated with increasing proteinuria and decreasing eGFR even after adjustments for age, sex and percentage of body fat. This study suggests that in RTR of a low-latitude city hypovitaminosis D is common, and is associated with excessive body fat, decreased eGFR and increased proteinuria.
An optimal error estimate in stochastic homogenization of discrete elliptic equations
Gloria, Antoine; 10.1214/10-AAP745
2012-01-01
This paper is the companion article to [Ann. Probab. 39 (2011) 779--856]. We consider a discrete elliptic equation on the $d$-dimensional lattice $\\mathbb{Z}^d$ with random coefficients $A$ of the simplest type: They are identically distributed and independent from edge to edge. On scales large w.r.t. the lattice spacing (i.e., unity), the solution operator is known to behave like the solution operator of a (continuous) elliptic equation with constant deterministic coefficients. This symmetric "homogenized" matrix $A_{\\mathrm{hom}}=a_{\\mathrm{hom}}\\mathrm{Id}$ is characterized by $\\xi\\cdot A_{\\mathrm{hom}}\\xi=$ for any direction $\\xi\\in\\mathbb{R}^d$, where the random field $\\phi$ (the "corrector") is the unique solution of $-\
Estimates for the Green function and singular solutions for polyharmonic nonlinear equation
Directory of Open Access Journals (Sweden)
Imed Bachar
2003-01-01
Full Text Available We establish a new form of the 3G theorem for polyharmonic Green function on the unit ball of ℝn(n≥2 corresponding to zero Dirichlet boundary conditions. This enables us to introduce a new class of functions Km,n containing properly the classical Kato class Kn. We exploit properties of functions belonging to Km,n to prove an infinite existence result of singular positive solutions for nonlinear elliptic equation of order 2m.
Estimate of Accuracy of Solution of the Nonlocal Fisher-Kolomogorov-Petrovskii-Piskunov Equation
Levchenko, E. A.; Trifonov, A. Yu.; Shapovalov, A. V.
2013-05-01
The discrepancy of semiclassical asymptotics for the one-dimensional nonlocal Fisher-Kolmogorov-Petrovskii-Piskunov equation is investigated. It is shown that there exist values of the parameters of the system, for which the norm of the discrepancy is bounded and the accuracy of the asymptotic solution is preserved over the entire time interval, but also values of the parameters, for which the discrepancy tends to zero, and the asymptotic solution tends to the exact one.
[New topics regarding equations for GFR estimation based on serum creatinine and cystatin C].
Horio, Masaru
2014-02-01
Japanese GFR equations and CKD-EPI equations based on standardized serum creatinine and standardized cystatin C are recommended in recent Japanese CKD guides and KDIGO guidelines for CKD management, respectively. CKD-EPIcreat overestimates GFR in Japanese subjects, probably due to the difference in muscle mass between Japanese and Caucasians. Unlike CKD-EPIcreat, CKD-EPIcys performs well in Japanese subjects, indicating the advantages of using cystatin C as a GFR marker. KDIGO guidelines suggest measuring eGFRcys in adults with eGFRcreat of 45-59 ml/min/1.73 m2 who do not have markers of kidney damage if confirmation of CKD is required. Creatinine is excreted by glomerular filtration, but also secreted by the tubules. Alteration of the tubular secretion of creatinine may influence the performance of GFR equations based on serum creatinine. Multivariate analysis showed that GFR and serum albumin levels were independent parameters affecting the fractional excretion of creatinine (FE-Cr). Alteration of FE-Cr according to the serum albumin levels may be one of the reasons for the bias of GFR equations based on serum creatinine. Low GFR is a risk factor for all-cause and cardiovascular mortality in a general population. However, the relationship between eGFR and the hazard risk of events is different depending on whether cystatin C or creatinine is used to calculate eGFR. The association between eGFRcys and the hazard risk is much stronger compared with eGFRcreat. Cystatin C may be a useful alternative to creatinine for detecting a high risk of complications in a general population and subjects with CKD.
Verbitsky, Anton
2014-01-01
We consider the discrete nonlinear stationary Schrödinger equation on a bounded n-dimensional box and on the whole space. In the first case we derive the existence of a positive classical solution of the corresponding continuous problem from a uniform a priori bound on positive discrete solutions for a general right hand side. In the second case we derive a uniform a priori bound on positive discrete solutions for the Schrödinger-type nonlinearity.
Sánchez, Ana; Vázquez, José A; Quinteiro, Javier; Sotelo, Carmen G
2013-04-10
Real-time PCR is the most sensitive method for detection and precise quantification of specific DNA sequences, but it is not usually applied as a quantitative method in seafood. In general, benchmark techniques, mainly cycle threshold (Ct), are the routine method for quantitative estimations, but they are not the most precise approaches for a standard assay. In the present work, amplification data from European hake (Merluccius merluccius) DNA samples were accurately modeled by three sigmoid reparametrized equations, where the lag phase parameter (λc) from the Richards equation with four parameters was demonstrated to be the perfect substitute for Ct for PCR quantification. The concentrations of primers and probes were subsequently optimized by means of that selected kinetic parameter. Finally, the linear correlation among DNA concentration and λc was also confirmed.
Directory of Open Access Journals (Sweden)
Shafi Tariq
2012-06-01
Full Text Available Abstract Background The Chronic Kidney Disease Epidemiology Collaboration equation for estimation of glomerular filtration rate (eGFRCKD-EPI improves GFR estimation compared with the Modification of Diet in Renal Disease Study equation (eGFRMDRD but its association with mortality in a nationally representative population sample in the US has not been studied. Methods We examined the association between eGFR and mortality among 16,010 participants of the Third National Health and Nutrition Examination Survey (NHANES III. Primary predictors were eGFRCKD-EPI and eGFRMDRD. Outcomes of interest were all-cause and cardiovascular disease (CVD mortality. Improvement in risk categorization with eGFRCKD-EPI was evaluated using adjusted relative hazard (HR and Net Reclassification Improvement (NRI. Results Overall, 26.9% of the population was reclassified to higher eGFR categories and 2.2% to lower eGFR categories by eGFRCKD-EPI, reducing the proportion of prevalent CKD classified as stage 3–5 from 45.6% to 28.8%. There were 3,620 deaths (1,540 from CVD during 215,082 person-years of follow-up (median, 14.3 years. Among those with eGFRMDRD 30–59 ml/min/1.73 m2, 19.4% were reclassified to eGFRCKD-EPI 60–89 ml/min/1.73 m2 and these individuals had a lower risk of all-cause mortality (adjusted HR, 0.53; 95% CI, 0.34-0.84 and CVD mortality (adjusted HR, 0.51; 95% CI, 0.27-0.96 compared with those not reclassified. Among those with eGFRMDRD >60 ml/min/1.73 m2, 0.5% were reclassified to lower eGFRCKD-EPI and these individuals had a higher risk of all-cause (adjusted HR, 1.31; 95% CI, 1.01-1.69 and CVD (adjusted HR, 1.42; 95% CI, 1.01-1.99 mortality compared with those not reclassified. Risk prediction improved with eGFRCKD-EPI; NRI was 0.21 for all-cause mortality (p Conclusions eGFRCKD-EPI categories improve mortality risk stratification of individuals in the US population. If eGFRCKD-EPI replaces eGFRMDRD in the US, it will likely
Energy Technology Data Exchange (ETDEWEB)
Arora, H.S. [School of Mechanical, Material and Energy Engineering, Indian Institute of Technology Ropar, Rupnagar, Punjab 140001 (India); Singh, H., E-mail: harpreetsingh@iitrpr.ac.in [School of Mechanical, Material and Energy Engineering, Indian Institute of Technology Ropar, Rupnagar, Punjab 140001 (India); Dhindaw, B.K. [School of Materials and Mineral Resources, Universiti Sains Malaysia, Engineering Campus, Nibong Tebal, Pulau Penang 14300 (Malaysia)
2012-05-01
Highlights: Black-Right-Pointing-Pointer Magnesium alloy AE42 was friction stir processed under different cooling conditions. Black-Right-Pointing-Pointer Heat flow model was developed using finite difference heat equations. Black-Right-Pointing-Pointer Generalized MATLAB code was developed for solving heat flow model. Black-Right-Pointing-Pointer Regression equation for estimation of grain size was developed. - Abstract: The present investigation is aimed at developing a heat flow model to simulate temperature history during friction stir processing (FSP). A new approach of developing implicit form of finite difference heat equations solved using MATLAB code was used. A magnesium based alloy AE42 was friction stir processed (FSPed) at different FSP parameters and cooling conditions. Temperature history was continuously recorded in the nugget zone during FSP using data acquisition system and k type thermocouples. The developed code was validated at different FSP parameters and cooling conditions during FSP experimentation. The temperature history at different locations in the nugget zone at different instants of time was further utilized for the estimation of grain growth rate and final average grain size of the FSPed specimen. A regression equation relating the final grain size, maximum temperature during FSP and the cooling rate was developed. The metallurgical characterization was done using optical microscopy, SEM, and FIB-SIM analysis. The simulated temperature profiles and final average grain size were found to be in good agreement with the experimental results. The presence of fine precipitate particles generated in situ in the investigated magnesium alloy also contributed in the evolution of fine grain structure through Zener pining effect at the grain boundaries.
Broekroelofs, J; Stegeman, CA; Navis, GJ; de Haan, J; van der Bij, W; de Zeeuw, D; de Jong, PE
2000-01-01
Background: Progressive renal function loss during long-term follow up is common after lung transplantation and close monitoring is warranted, Since changes in creatinine generation and excretion may occur after lung transplantation, the reliability of creatinine-based methods of renal function asse
On the spectral theory and dispersive estimates for a discrete Schrödinger equation in one dimension
Pelinovsky, D. E.; Stefanov, A.
2008-11-01
Based on the recent work [Komech et al., "Dispersive estimates for 1D discrete Schrödinger and Klein-Gordon equations," Appl. Anal. 85, 1487 (2006)] for compact potentials, we develop the spectral theory for the one-dimensional discrete Schrödinger operator, Hϕ =(-Δ+V)ϕ=-(ϕn +1+ϕn -1-2ϕn)+Vnϕn. We show that under appropriate decay conditions on the general potential (and a nonresonance condition at the spectral edges), the spectrum of H consists of finitely many eigenvalues of finite multiplicities and the essential (absolutely continuous) spectrum, while the resolvent satisfies the limiting absorption principle and the Puiseux expansions near the edges. These properties imply the dispersive estimates ||eitHPa.c.(H)||lσ2→l-σ2≲t-3/2 for any fixed σ >5/2 and any t >0, where Pa.c.(H) denotes the spectral projection to the absolutely continuous spectrum of H. In addition, based on the scattering theory for the discrete Jost solutions and the previous results by Stefanov and Kevrekidis ["Asymptotic behaviour of small solutions for the discrete nonlinear Schrödinger and Klein-Gordon equations," Nonlinearity 18, 1841 (2005)], we find new dispersive estimates ||eitH Pa.c.(H)||l1→l∞≲t-1/3, which are sharp for the discrete Schrödinger operators even for V =0.
Williams-Sether, Tara
2015-08-06
Annual peak-flow frequency data from 231 U.S. Geological Survey streamflow-gaging stations in North Dakota and parts of Montana, South Dakota, and Minnesota, with 10 or more years of unregulated peak-flow record, were used to develop regional regression equations for exceedance probabilities of 0.5, 0.20, 0.10, 0.04, 0.02, 0.01, and 0.002 using generalized least-squares techniques. Updated peak-flow frequency estimates for 262 streamflow-gaging stations were developed using data through 2009 and log-Pearson Type III procedures outlined by the Hydrology Subcommittee of the Interagency Advisory Committee on Water Data. An average generalized skew coefficient was determined for three hydrologic zones in North Dakota. A StreamStats web application was developed to estimate basin characteristics for the regional regression equation analysis. Methods for estimating a weighted peak-flow frequency for gaged sites and ungaged sites are presented.
Directory of Open Access Journals (Sweden)
Samia Rafael Yamashita
2015-02-01
Full Text Available Objective: To determine the presence of linear relationship between renal cortical thickness, bipolar length, and parenchymal thickness in chronic kidney disease patients presenting with different estimated glomerular filtration rates (GFRs and to assess the reproducibility of these measurements using ultrasonography. Materials and Methods: Ultrasonography was performed in 54 chronic renal failure patients. The scans were performed by two independent and blinded radiologists. The estimated GFR was calculated using the Cockcroft-Gault equation. Interobserver agreement was calculated and a linear correlation coefficient (r was determined in order to establish the relationship between the different renal measurements and estimated GFR. Results: The correlation between GFR and measurements of renal cortical thickness, bipolar length, and parenchymal thickness was, respectively, moderate (r = 0.478; p < 0.001, poor (r = 0.380; p = 0.004, and poor (r = 0.277; p = 0.116. The interobserver agreement was considered excellent (0.754 for measurements of cortical thickness and bipolar length (0.833, and satisfactory for parenchymal thickness (0.523. Conclusion: The interobserver reproducibility for renal measurements obtained was good. A moderate correlation was observed between estimated GFR and cortical thickness, but bipolar length and parenchymal thickness were poorly correlated.
Renal dysfunction in patients with heart failure with preserved versus reduced ejection fraction
DEFF Research Database (Denmark)
McAlister, Finlay A; Ezekowitz, Justin; Tarantini, Luigi
2012-01-01
Prior studies in heart failure (HF) have used the Modification of Diet in Renal Disease (MDRD) equation to calculate estimated glomerular filtration rate (eGFR). The Chronic Kidney Disease-Epidemiology Collaboration Group (CKD-EPI) equation provides a more-accurate eGFR than the MDRD when compare...
Barth, Nancy A.; Veilleux, Andrea G.
2012-01-01
estimates were then used to develop a set of equations for estimating flows with 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities for ungaged basins. The final equations are functions of drainage area.Average standard errors of prediction for these regression equations range from 214.2 to 856.2 percent.
Solutions to $ar{partial}$-equations on strongly pseudo-convex domains with $L^p$-estimates
Directory of Open Access Journals (Sweden)
Osama Abdelkader
2004-05-01
Full Text Available We construct a solution to the $ar{partial}$-equation on a strongly pseudo-convex domain of a complex manifold. This is done for forms of type $(0,s$, $sgeq 1 $, with values in a holomorphic vector bundle which is Nakano positive and for complex valued forms of type $(r,s$, $1leq rleq n$, when the complex manifold is a Stein manifold. Using Kerzman's techniques, we find the $L^p$-estimates, $1leq pleq infty$, for the solution.
Directory of Open Access Journals (Sweden)
Sandjo Albert N.
2014-01-01
Full Text Available We establish the well-posedness of boundary value problems for a family of nonlinear higherorder parabolic equations which comprises some models of epitaxial growth and thin film theory. In order to achieve this result, we provide a unified framework for constructing local mild solutions in C0([0, T]; Lp(Ω by introducing appropriate time-weighted Lebesgue norms inspired by a priori estimates of solutions. This framework allows us to obtain global existence of solutions under the proviso that initial data are reasonably small
Current Concepts in the Diagnosis and Classification of Renal Dysfunction in Cirrhosis
Mindikoglu, Ayse L.; Weir, Matthew R.
2013-01-01
Background Renal dysfunction is one of the most common complications of cirrhosis with high morbidity and mortality. Summary In subjects with cirrhosis, renal dysfunction can present either as a direct consequence of cirrhosis (e.g. hepatorenal syndrome Type I and Type II) or secondary to etiologies other than cirrhosis (chronic kidney disease due to diabetic nephropathy, prerenal azotemia). Or, patients with cirrhosis may have renal dysfunction resulting directly from cirrhosis; and an underlying chronic kidney disease. Key Messages Given the challenges in the differential diagnosis of renal dysfunction and insufficient accuracy of serum creatinine and creatinine-based glomerular filtration rate estimating equations in cirrhosis, there is an urgent need for more accurate biomarkers of renal dysfunction in this population. This review will discuss novel concepts for the diagnosis and classification of renal dysfunction in cirrhosis to overcome at least some of the diagnostic and therapeutic challenges. Additionally, a new classification will be proposed for renal dysfunction in cirrhosis. PMID:24107793
Large deviation tail estimates and related limit laws for stochastic fixed point equations
DEFF Research Database (Denmark)
Collamore, Jeffrey F.; Vidyashankar, Anand N.
2013-01-01
between the forward and backward recursions and develop techniques for estimating the exceedance probability. In the process, we establish an interesting connection between the regularity properties of $\\{V_n\\}$ and the recurrence properties of an associated $\\xi$-shifted Markov chain. We illustrate...
Large deviation tail estimates and related limit laws for stochastic fixed point equations
DEFF Research Database (Denmark)
Collamore, Jeffrey F.; Vidyashankar, Anand N.
2013-01-01
}, D_n\\} +B_n$, where $\\{ (A_n,B_n,D_n): n \\in \\pintegers \\}$ is an i.i.d.\\ sequence of random variables. Next, we consider recursions where the driving sequence of vectors, $\\{(A_n, B_n, D_n): n \\in \\pintegers \\}$, is modulated by a Markov chain in general state space. We demonstrate an asymmetry......We study the forward and backward recursions generated by a stochastic fixed point equation (SFPE) of the form $V \\stackrel{d}{=} A\\max\\{V, D\\}+B$, where $(A, B, D) \\in (0, \\infty)\\times {\\mathbb R}^2$, for both the stationary and explosive cases. In the stationary case (when ${\\bf E} [\\log \\: A......] 0)$, we establish a central limit theorem for the forward recursion generated by the SFPE, namely the process $V_n= A_n \\max\\{V_{n-1...
Existence and decay estimates of solutions to complex Ginzburg-Landau type equations
Shimotsuma, Daisuke; Yokota, Tomomi; Yoshii, Kentarou
2016-02-01
This paper deals with the initial-boundary value problem (denoted by (CGL)) for the complex Ginzburg-Landau type equation ∂u/∂t - (λ + iα) Δu + (κ + iβ)| u | q - 1 u - γu = 0 with initial data u0 ∈Lp (Ω) in the case 1 0, α , β , γ , κ ∈ R. There are a lot of studies on local and global existence of solutions to (CGL) including the physically relevant case q = 3 and κ > 0. This paper gives existence results with precise properties of solutions and rigorous proof from a mathematical point of view. The physically relevant case can be considered as a special case of the results. Moreover, in the case κ inequality with Re .
Exceptional points for parameter estimation in open quantum systems: Analysis of the Bloch equations
Am-Shallem, Morag; Moiseyev, Nimrod
2014-01-01
The dynamics of open quantum systems is typically described by a quantum dynamical semigroup generator ${\\cal L}$. The eigenvalues of ${\\cal L}$ are complex, reflecting unitary as well as dissipative dynamics. For certain values of parameters defining ${\\cal L}$, non-hermitian degeneracies emerge, i.e. exceptional points ($EP$). We study the implications of such points in the open system dynamics of a two-level-system described by the Bloch equation. This open system has become the paradigm of diverse fields in physics, from NMR to quantum information and elementary particles. We find as a function of detuning and driving amplitude a continuous line of exceptional points merging into two cusps of triple degeneracy. The dynamical signature of these $EP$ points is a unique time evolution. This unique feature can be employed experimentally to locate the $EP$ points and thereby to determine the intrinsic system parameters for any desired accuracy.
Derivation of an equation to estimate marrow content of bovine cervical vertebrae.
Gebault, R A; Field, R A; Means, W J; Russell, W C
1998-08-01
Marrow content of bovine cervical vertebrae from Choice- and Select-grade carcasses weighing 294 to 343 kg was determined so that a method to monitor the amount of marrow in meat from advanced meat/bone separation machinery and recovery (AMR) systems could be developed. The marrow determination requires cleaning and then ashing bones. Because a large difference in ash content of bone and bone marrow exists and because cartilage content of cervical vertebrae in Choice and Select beef is relatively constant, it was possible to derive the following equation: Weight of marrow = [weight of cartilage (% ash in cartilage - % ash in bone) + % ash in bone (total weight) - (total ash)]/[(% ash in bone - % ash in marrow)]. Constants for ash in fresh bone, marrow, and cartilage were 58.51, .57, and 2.14% with SD of 2.23, .15, and .30%, respectively. A cartilage content of 9.5% along with cervical vertebrae weight and total ash weight were also used to calculate 33.9% marrow in cervical vertebrae. Means for marrow pressed or centrifuged from bovine cervical vertebrae were lower than those obtained from the equation. Therefore, pressing and centrifuging left some marrow in spongy bone. Our ashing method for determining the amount of marrow in whole cervical vertebrae should be useful for determining marrow remaining in cervical vertebrae of bone cakes from AMR systems. Percentage ash in pressed bones is higher and the calculated marrow content is lower when pressed bones are compared to cervical vertebrae that are not pressed. The amount of marrow in whole cervical vertebrae minus the amount left in cervical vertebrae from bone cakes equals the amount in meat from AMR systems.
Cavalcanti, Marcelo M.; Corrêa, Wellington J.; Domingos Cavalcanti, Valéria N.; Tebou, Louis
2017-02-01
In this paper, we study the existence at the H1-level as well as the stability for the damped defocusing Schrödinger equation in Rd. The considered damping coefficient is time-dependent and may vanish at infinity. To prove the existence, we employ the method devised by Özsarı, Kalantarov and Lasiecka [27], which is based on monotone operators theory. In particular, when d = 1 or d = 2, we obtain the uniqueness. Decay estimates for the L2-level and (H1 ∩L p + 2)-level energies are established with the help of direct multipliers method, coupled with refined energy estimates and a lower semi-continuity argument.
Estimating Equations in the Presence of Missing Data%带有缺失数据的估计方程
Institute of Scientific and Technical Information of China (English)
赵慧秀; 马文卿
2009-01-01
This paper provides a new method to solve the problem of estimating equations with missing data. In this method, a function of observed data is used to adjust for the function of missing data. The more information about missing mechanism is known, the move efficient of the estimates obtained by using the method.%给出了一种解决估计方程中的缺失数据问题的新方法:用一种观测数据的函数来调整缺失数据的函数.当我们对于缺失机制的信息知道的越多,由此种方法得到的估计的效越高.
Alqasemi, Umar; Salehi, Hassan S.; Zhu, Quing
2016-01-01
This paper reports a method of estimating an approximate closed-form solution to the light diffusion equation for any type of geometry involving Dirichlet’s boundary condition with known source location. It is based on estimating the optimum locations of multiple imaginary point sources to cancel the fluence at the extrapolated boundary by constrained optimization using a genetic algorithm. The mathematical derivation of the problem to approach the optimum solution for the direct-current type of diffuse optical systems is described in detail. Our method is first applied to slab geometry and compared with a truncated series solution. After that, it is applied to hemispherical geometry and compared with Monte Carlo simulation results. The method provides a fast and sufficiently accurate fluence distribution for optical reconstruction. PMID:26831771
Directory of Open Access Journals (Sweden)
Dilip C Nath
2011-07-01
Full Text Available The Quasi-Least Squares (QLS is useful for different correlation structure with attachment of Generalized Estimating Equation (GEE. The purpose of this work is to compare the regression parameter in the presence of different correlation structure with respect to GEE and QLS method. The comparison of estimated regression parameter has been performed in clinical trial data set; studying the effect of drug treatment (metformin with pioglitazone Vs (gliclazide with pioglitazone in type 2 diabetes patients. In case of QLS, the correlation coefficient of post-parandinal blood sugar (PPBS under tridiagonal correlation is 0.008 while it failed to produce by GEE. It has been found that the combination of metformin with pioglitazone is more effective as compared to the combination of gliclazide with pioglitazone.
Gradient-based estimation of uncertain parameters for elliptic partial differential equations
Borggaard, Jeff; van Wyk, Hans-Werner
2015-06-01
This paper discusses the estimation of uncertain distributed diffusion coefficients in elliptic systems based on noisy measurements of the model output. We treat the parameter identification problem as a variational problem over the appropriate stochastic Sobolev spaces and show that minimizers exist and satisfy a saddle point condition. Although a lack of regularity precludes the direct use of gradient-based optimization techniques, a spectral approximation of the observation field allows us to estimate the original problem by a smooth, albeit high dimensional, deterministic optimization problem, the so-called finite noise problem, which lends itself readily to more traditional optimization approaches. We prove that the finite noise minimizers converge to the appropriate infinite dimensional ones, and devise and analyze a stochastic augmented Lagrangian method for locating these numerically. We also discuss the numerical discretization of the finite noise problem, using sparse grid hierarchical finite elements, and present three numerical examples to illustrate our method.
Directory of Open Access Journals (Sweden)
Stuker Florian
2010-06-01
Full Text Available Abstract Background Non-invasive planar fluorescence reflectance imaging (FRI is used for accessing physiological and molecular processes in biological tissue. This method is efficiently used to detect superficial fluorescent inclusions. FRI is based on recording the spatial radiance distribution (SRD at the surface of a sample. SRD provides information for measuring structural parameters of a fluorescent source (such as radius and depth. The aim of this article is to estimate the depth and radius of the source distribution from SRD, measured at the sample surface. For this reason, a theoretical expression for the SRD at the surface of a turbid sample arising from a spherical light source embedded in the sample, was derived using a steady-state solution of the diffusion equation with an appropriate boundary condition. Methods The SRD was approximated by solving the diffusion equation in an infinite homogeneous medium with solid spherical sources in cylindrical geometry. Theoretical predications were verified by experiments with fluorescent sources of radius 2-6 mm embedded at depths of 2-4 mm in a tissue-like phantom. Results The experimental data were compared with the theoretical values which shows that the root mean square (RMS error in depth measurement for nominal depth values d = 2, 2.5, 3, 3.5, 4 mm amounted to 17%, 5%, 2%, 1% and 5% respectively. Therefore, the average error in depth estimation was ≤ 4% for depths larger than the photon mean free path. Conclusions An algorithm is proposed that allows estimation of the location and radius of a spherical source in a homogeneous tissue-like phantom by accounting for anisotropic light scattering effect using FRI modality. Surface SRD measurement enabled accurate estimates of fluorescent depth and radius in FRI modality, and can be used as an element of a more general tomography reconstruction algorithm.
Directory of Open Access Journals (Sweden)
Fernando Da Silva
2015-02-01
Full Text Available Allometric models to estimate biomass components such as stem mass Ms, foliage mass Ml, root mass Mr and aboveground mass Ma, were developed for the palm species Euterpe precatoria Mart., which is the most abundant tree species in the Amazon. We harvested twenty palms including above- and below-ground parts in an old growth Amazonian forest in Brazil. The diameter at breast height D ranged from 3.9–12.7 cm, and the stem height H ranged from 2.3–16.4 m. The D, diameter at ground basis D0, crown diameter CD, H, stem specific gravity ρ, and number of fronds Nf were considered as independent variables and incorporated into a power function model. The best predictors were D2Hρ for Ms and Ma, D2HNf for Ml, and D for Mr. Slender index (H/D ranged from 0.56–1.46 m·cm−1, and the D-H relationship suggested that the stem shape becomes more slender with increasing D. On the other hand, ρ increased with D implying a stiffening of stem tissue. The average root/shoot ratio was estimated as 0.29 which was higher than that reported for the non-palm tree species in the Amazon. Comparisons of several models to estimate Ma of different palm species, suggested that the variations of the D-H relationship and ρ should be considered to develop allometric models for estimating biomass in palm species. In particular the ρ largely varied depending on individual size, which should be important to consider, when developing the allometric models for palms.
Hirai, Toshinori; Kimura, Toshimi; Echizen, Hirotoshi
2016-01-01
Whether renal dysfunction influences the hypouricemic effect of febuxostat, a xanthine oxidase (XO) inhibitor, in patients with hyperuricemia due to overproduction or underexcretion of uric acid (UA) remains unclear. We aimed to address this question with a modeling and simulation approach. The pharmacokinetics (PK) of febuxostat were analyzed using data from the literature. A kinetic model of UA was retrieved from a previous human study. Renal UA clearance was estimated as a function of creatinine clearance (CLcr) but non-renal UA clearance was assumed constant. A reversible inhibition model for bovine XO was adopted. Integrating these kinetic formulas, we developed a PK-pharmacodynamic (PK-PD) model for estimating the time course of the hypouricemic effect of febuxostat as a function of baseline UA level, febuxostat dose, treatment duration, body weight, and CLcr. Using the Monte Carlo simulation method, we examined the performance of the model by comparing predicted UA levels with those reported in the literature. We also modified the models for application to hyperuricemia due to UA overproduction or underexcretion. Thirty-nine data sets comprising 735 volunteers or patients were retrieved from the literature. A good correlation was observed between the hypouricemic effects of febuxostat estimated by our PK-PD model and those reported in the articles (observed) (r=0.89, p<0.001). The hypouricemic effect was estimated to be augmented in patients with renal dysfunction irrespective of the etiology of hyperuricemia. While validation in clinical studies is needed, the modeling and simulation approach may be useful for individualizing febuxostat doses in patients with various clinical characteristics.
Institute of Scientific and Technical Information of China (English)
Rami; Riziq-Yousef; Abumuaileq; Emad; Abu-Assi; Andrea; López-López; Sergio; Raposeiras-Roubin; Moisés; RodríguezMa?ero; Luis; Martínez-Sande; Francisco; Javier; García-Seara; Xesus; Alberte; Fernandez-López; Jose; Ramón; GonzálezJuanatey
2015-01-01
AIM: To compare the performance of the re-expressed Modification of Diet in Renal Disease equation vs the new Chronic Kidney Disease Epidemiology Collaboration equation in patients with non-valvular atrial fibrillation.METHODS: We studied 911 consecutive patients with non-valvular atrial fibrillation on vitamin-K antagonist. The performance of the re-expressed Modification of Diet in Renal Disease equation vs the new Chronic Kidney Disease Epidemiology Collaboration equation in patients with non-valvular atrial fibrillation with respect to either a composite endpoint of major bleeding, thromboembolic events and all-cause mortality or each individual component of the composite endpoint was assessed using continuous and categorical ≥ 60, 59-30, and < 30 m L/min per 1.73 m2 estimated glomerular filtration rate.RESULTS: During 10 ± 3 mo, the composite endpoint occurred in 98(10.8%) patients: 30 patients developed major bleeding, 18 had thromboembolic events, and 60 died. The new equation provided lower prevalence of renal dysfunction < 60 m L/min per 1.73 m2(32.9%),compared with the re-expressed equation(34.1%). Estimated glomerular filtration rate from both equations was independent predictor of composite endpoint(HR = 0.98 and 0.97 for the re-expressed and the new equation, respectively; P < 0.0001) and all-cause mortality(HR = 0.98 for both equations, P < 0.01). Strong association with thromboembolic events was observed only when estimated glomerular filtration rate was < 30 m L/min per 1.73 m2: HR is 5.1 for the re-expressed equation, and HR = 5.0 for the new equation. No significant association with major bleeding was observed for both equations.CONCLUSION: The new equation reduced the prevalence of renal dysfunction. Both equations performed similarly in predicting major adverse outcomes.
Energy Technology Data Exchange (ETDEWEB)
Fournier, D.; Le Tellier, R.; Suteau, C., E-mail: damien.fournier@cea.fr, E-mail: romain.le-tellier@cea.fr, E-mail: christophe.suteau@cea.fr [CEA, DEN, DER/SPRC/LEPh, Cadarache, Saint Paul-lez-Durance (France); Herbin, R., E-mail: raphaele.herbin@cmi.univ-mrs.fr [Laboratoire d' Analyse et de Topologie de Marseille, Centre de Math´ematiques et Informatique (CMI), Universit´e de Provence, Marseille Cedex (France)
2011-07-01
The solution of the time-independent neutron transport equation in a deterministic way invariably consists in the successive discretization of the three variables: energy, angle and space. In the SNATCH solver used in this study, the energy and the angle are respectively discretized with a multigroup approach and the discrete ordinate method. A set of spatial coupled transport equations is obtained and solved using the Discontinuous Galerkin Finite Element Method (DGFEM). Within this method, the spatial domain is decomposed into elements and the solution is approximated by a hierarchical polynomial basis in each one. This approach is time and memory consuming when the mesh becomes fine or the basis order high. To improve the computational time and the memory footprint, adaptive algorithms are proposed. These algorithms are based on an error estimation in each cell. If the error is important in a given region, the mesh has to be refined (h−refinement) or the polynomial basis order increased (p−refinement). This paper is related to the choice between the two types of refinement. Two ways to estimate the error are compared on different benchmarks. Analyzing the differences, a hp−refinement method is proposed and tested. (author)
Chimonas, Theodoros; Athyros, Vassilios G; Ganotakis, Emmanouel; Nicolaou, Vassilios; Panagiotakos, Demosthenes B; Mikhailidis, Dimitri P; Elisaf, Moses
2010-01-01
We investigated cardiovascular disease (CVD) risk factors in 1501 Greeks (613 men and 888 women, aged 40-65 years) referred to outpatients with metabolic syndrome (MetS) and without diabetes mellitus or CVD. The 10-year risk of fatal CVD events was calculated using European Society of Cardiology Systematic Coronary Risk Estimation (ESC SCORE), Hellenic-SCORE, and Framingham equations. Raised blood pressure (BP) and hypertriglyceridemia were more common in men (89.6% vs 84.2% and 86.8% vs 74.2%, respectively; P < .001). Low high-density lipoprotein cholesterol (HDL-C) and abdominal obesity were more common in women (58.2% vs 66.2% and 85.8% vs 97.1%, respectively; P < .001). The 10-year risk of fatal CVD events using HellenicSCORE was higher in men (6.3% +/- 4.3% vs 2.7% +/- 2.1%; P < .001). European Society of Cardiology Systematic Coronary Risk Estimation and Framingham yielded similar results. The risk equations gave similar assessments in a European Mediterranean population except for HellenicSCORE that calculated more MetS women requiring risk modification. This might justify local risk engine evaluation in event-based studies. (Clinical-Trials.gov ID: NCT00416741).
Institute of Scientific and Technical Information of China (English)
汪秀英; 黄蕾蕾; 宋慧; 丁伟洁; 陈茂杰; 卓朗
2011-01-01
Objective To investigate the features of each glomerular filtration rate (GFR) equation in calculating the estimated glomerular filtration rate (eGFR) among mass samples, and to provide guidance to the appropriate equation selections of in the estimation of eGFR. Methods The mass samples were based on the physical examination data in recent years in Xuzhou. Simplified MDRD equation, modified MDRD equation, racial coefficient equation and Ruijin equation were designated to compare differences in statistic indexes and evaluate each equation via dynamic diagrammatic trends. Results Of the four equations, the means of eGFR by simplified MDRD equation were approximate to those by modified MDRD equation, with those by Ruijin equation at the nadir and those by racial coefficient equation at the peak.The standardized rate of reduced renal function was 0.53％, 0.45％, 0.62％ and 0. 17％, respectively. The standardized rate of chronic kidney disease (CKD) was 11.71％, 11.66％, 11.81％ and 11.46％, respectively. Conclusion The CKD in population study consists in hematuria and proteinuria, with little bias between different equations. Simplified MDRD equation or modified MDRD equation is still preferable in the study of the prevalence of CKD until new biochemical indicator is adopted to substitute serum creatinine so as to facilitate horizontal and vertical comparisons among relevant studies.%目的 通过使用不同的肾小球滤过率(GFR)公式估计人群的估计GFR(eGFR),了解不同公式的特征,指导正确选用公式有效估计eGFR.方法 本研究使用徐州地区近年来健康体检者的资料,比较简化MDRD公式、国内改良MDRD公式、种族系数公式和瑞金方程,比较各种统计指标之间的差异,通过图表的动态变化来判断各公式的价值.结果 简化MDRD公式的eGFR值与国内改良MDRD公式接近,瑞金方程最低,种族系数公式最高.肾功能下降标化患病率依次为0.53%、0.45%、0.62%、0.17%,慢
Goswami, Deepjyoti
2013-05-01
In the first part of this article, a new mixed method is proposed and analyzed for parabolic integro-differential equations (PIDE) with nonsmooth initial data. Compared to the standard mixed method for PIDE, the present method does not bank on a reformulation using a resolvent operator. Based on energy arguments combined with a repeated use of an integral operator and without using parabolic type duality technique, optimal L2 L2-error estimates are derived for semidiscrete approximations, when the initial condition is in L2 L2. Due to the presence of the integral term, it is, further, observed that a negative norm estimate plays a crucial role in our error analysis. Moreover, the proposed analysis follows the spirit of the proof techniques used in deriving optimal error estimates for finite element approximations to PIDE with smooth data and therefore, it unifies both the theories, i.e., one for smooth data and other for nonsmooth data. Finally, we extend the proposed analysis to the standard mixed method for PIDE with rough initial data and provide an optimal error estimate in L2, L 2, which improves upon the results available in the literature. © 2013 Springer Science+Business Media New York.
Variational Estimation of Wave-affected Parameters in a Two-equation Turbulence Model
2014-01-01
time 2 intervals within the assimilation window, where ijT , and obsT are the simulated and 3 observed temperature at location i and time level j. N...16 downwelling. Journal of Physical Oceanography, 32: 2171-2193. 17 Agrawal, Y.C., Terray, E.A., Donelan, M.A., Hwang, P.A., Williams , A. J...Y., Drennan, W.M., Kahma, K., Williams III, A. 7 J., Hwang, P., Kitaigorodskii, S. A., 1996. Estimates of kinetic energy 8 dissipation under
Estimating forest net primary production under changing climate: adding pests into the equation.
Pinkard, E A; Battaglia, M; Roxburgh, S; O'Grady, A P
2011-07-01
The current approach to modelling pest impacts on forest net primary production (NPP) is to apply a constant modifier. This does not capture the large spatial and temporal variability in pest abundance and activity that can occur, meaning that overestimates or underestimates of pest impacts on forest NPP are likely. Taking a more mechanistic approach that incorporates an understanding of how physiology is influenced by pest attack, enables us to better capture system feedbacks and dynamics, thereby improving the capacity to predict into novel situations such as changing climate, and to account for both changes in pest activity and host responses to the growing environment now and into the future. We reviewed the effects of pests on forest NPP and found a range of responses and physiological mechanisms underlying those responses. Pest outbreaks can clearly be a major perturbation to forest NPP, and it seems likely that the frequency and intensity of pest outbreaks, and the ways in which host species respond to pest damage, will change in the future. We summarized these impacts in the form of a conceptual model at leaf, tree and stand scales, and compared the physiological processes embedded within that framework with the capacity of a representative range of NPP models to capture those processes. We found that some models can encapsulate some of the processes, but no model can comprehensively account for the range of physiological responses to pest attack experienced by trees. This is not surprising, given the paucity of empirical data for most of the world's forests, and that the models were developed primarily for other purposes. We conclude with a list of the key physiological processes and pathways that need to be included in forest growth models in order to adequately capture pest impacts on forest NPP under current and future climate scenarios, the equations that might enable this and the empirical data required to support them.
Institute of Scientific and Technical Information of China (English)
LIANG Hui; ZHAO Wei; DAI Dejun; ZHANG Jun
2014-01-01
Diapycnal mixing is important in oceanic circulation. An inverse method in which a semi-explicit scheme is applied to discretize the one-dimensional temperature diffusion equation is established to estimate the vertical temperature diffusion coefficient based on the observed temperature profiles. The sensitivity of the inverse model in the idealized and actual conditions is tested in detail. It can be found that this inverse model has high feasibility under multiple situations ensuring the stability of the inverse model, and can be considered as an efficient way to estimate the temperature diffusion coefficient in the weak current regions of the ocean. Here, the hydrographic profiles from Argo floats are used to estimate the temporal and spatial distribution of the vertical mixing in the north central Pacific based on this inverse method. It is further found that the vertical mixing in the upper ocean displays a distinct seasonal variation with the amplitude decreasing with depth, and the vertical mixing over rough topography is stronger than that over smooth topography. It is suggested that the high-resolution profiles from Argo floats and a more reasonable design of the inverse scheme will serve to understand mixing processes.
Hayek, Mohamed
2016-06-01
A general analytical model for one-dimensional transient vertical infiltration is presented. The model is based on a combination of the Brooks and Corey soil water retention function and a generalized hydraulic conductivity function. This leads to power law diffusivity and convective term for which the exponents are functions of the inverse of the pore size distribution index. Accordingly, the proposed analytical solution covers many existing realistic models in the literature. The general form of the analytical solution is simple and it expresses implicitly the depth as function of water content and time. It can be used to model infiltration through semi-infinite dry soils with prescribed water content or flux boundary conditions. Some mathematical expressions of practical importance are also derived. The general form solution is useful for comparison between models, validation of numerical solutions and for better understanding the effect of some hydraulic parameters. Based on the analytical expression, a complete inverse procedure which allows the estimation of the hydraulic parameters from water content measurements is presented.
Directory of Open Access Journals (Sweden)
Liu X
2013-10-01
Full Text Available Xun Liu,1,2,* Huijuan Ma,1,* Hui Huang,3 Cheng Wang,1 Hua Tang,1 Ming Li,1 Yanni Wang,1 Tanqi Lou1 1Division of Nephrology, Department of Internal Medicine, The Third Affiliated Hospital of Sun Yat-sen University, 2College of Biology Engineering, South China University of Technology, 3Department of Cardiology, Sun Yat-sen Memorial Hospital of Sun Yat-sen University, Guangzhou, People's Republic of China*These authors contributed equally to the paperBackground: We aimed to evaluate the performance of the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI creatinine–cystatin C equation in a cohort of elderly Chinese participants.Materials and methods: Glomerular filtration rate (GFR was measured in 431 elderly Chinese participants by the technetium-99m diethylene-triamine-penta-acetic acid (99mTc-DTPA renal dynamic imaging method, and was calibrated equally to the dual plasma sample 99mTc-DTPA-GFR. Performance of the CKD-EPI creatinine–cystatin C equation was compared with the Cockroft–Gault equation, the re-expressed 4-variable Modification of Diet in Renal Disease (MDRD equation, and the CKD-EPI creatinine equation.Results: Although the bias of the CKD-EPI creatinine–cystatin C equation was greater than with the other equations (median difference, 5.7 mL/minute/1.73 m2 versus a range from 0.4–2.5 mL/minute/1.73 m2; P<0.001 for all, the precision was improved with the CKD-EPI creatinine–cystatin C equation (interquartile range for the difference, 19.5 mL/minute/1.73 m2 versus a range from 23.0–23.6 mL/minute/1.73 m2; P<0.001 for all comparisons, leading to slight improvement in accuracy (median absolute difference, 10.5 mL/minute/1.73 m2 versus 12.2 and 11.4 mL/minute/1.73 m2 for the Cockcroft–Gault equation and the re-expressed 4-variable MDRD equation, P=0.04 for both; 11.6 mL/minute/1.73 m2 for the CKD-EPI creatinine equation, P=0.11, as the optimal scores of performance (6.0 versus a range from 1.0–2.0 for the other
Feischl, Michael; Gantner, Gregor; Praetorius, Dirk
2015-06-01
We consider the Galerkin boundary element method (BEM) for weakly-singular integral equations of the first-kind in 2D. We analyze some residual-type a posteriori error estimator which provides a lower as well as an upper bound for the unknown Galerkin BEM error. The required assumptions are weak and allow for piecewise smooth parametrizations of the boundary, local mesh-refinement, and related standard piecewise polynomials as well as NURBS. In particular, our analysis gives a first contribution to adaptive BEM in the frame of isogeometric analysis (IGABEM), for which we formulate an adaptive algorithm which steers the local mesh-refinement and the multiplicity of the knots. Numerical experiments underline the theoretical findings and show that the proposed adaptive strategy leads to optimal convergence.
Enders, Craig K.; Peugh, James L.
2004-01-01
Two methods, direct maximum likelihood (ML) and the expectation maximization (EM) algorithm, can be used to obtain ML parameter estimates for structural equation models with missing data (MD). Although the 2 methods frequently produce identical parameter estimates, it may be easier to satisfy missing at random assumptions using EM. However, no…
Incidence and Predictors of End-Stage Renal Disease in Outpatients With Systolic Heart Failure
DEFF Research Database (Denmark)
Bosselmann, Helle Skovmand; Gislason, Gunnar; Gustafsson, Finn
2013-01-01
Background- Renal dysfunction is an important prognostic factor in heart failure (HF), but whether this dysfunction progresses to end-stage renal disease (ESRD) is unknown. Therefore, we examined incidence and predictors of ESRD in outpatients with HF. Methods and Results- Patients with systolic HF...... were identified in The Danish Heart Failure database and new-onset ESRD from the Danish Registry on Dialysis. Renal function was estimated by The Chronic Kidney Disease Epidemiology Collaboration equation and patients grouped by estimated glomerular filtration rate (eGFR)-group I: ≥60 mL/min per 1.73 m...
Schnitzer, S.; Seitz, F.; Eicker, A.; Güntner, A.; Wattenbach, M.; Menzel, A.
2013-06-01
For the estimation of soil loss by erosion in the strongly affected Chinese Loess Plateau we applied the Universal Soil Loss Equation (USLE) using a number of input data sets (monthly precipitation, soil types, digital elevation model, land cover and soil conservation measures). Calculations were performed in ArcGIS and SAGA. The large-scale soil erosion in the Loess Plateau results in a strong non-hydrological mass change. In order to investigate whether the resulting mass change from USLE may be validated by the gravity field satellite mission GRACE (Gravity Recovery and Climate Experiment), we processed different GRACE level-2 products (ITG, GFZ and CSR). The mass variations estimated in the GRACE trend were relatively close to the observed sediment yield data of the Yellow River. However, the soil losses resulting from two USLE parameterizations were comparatively high since USLE does not consider the sediment delivery ratio. Most eroded soil stays in the study area and only a fraction is exported by the Yellow River. Thus, the resultant mass loss appears to be too small to be resolved by GRACE.
McGurk, Ross J; Smith, Valerie A; Bowsher, James; Lee, John A; Das, Shiva K
2013-06-07
This study aims to quantify how filter choice affects several fluoro-deoxy-glucose (FDG)-positron emission tomography (PET) segmentation methods and present the use of model fitting via generalized estimating equations (GEEs) to appropriately account for the properties of a common segmentation quality metric (Dice similarity coefficient). Spherical and irregularly shaped 'hot' objects filled with 18F-FDG were placed in a medium with background activity and imaged for 1, 2 and 5 min durations at low and high contrasts. Images were filtered with Gaussian and bilateral filters of 5 and 7 mm full-width half maximum (FWHM), with and without 3 mm FWHM Gaussian pre-smoothing. Four segmentation methods were used: 40% thresholding, adaptive thresholding, k-means clustering and seeded region-growing. Segmentation accuracy was quantified by overlap (using Dice similarity coefficient (DSC)) and distance between surfaces (using symmetric-mean-absolute-surface-distance (SMASD)) of the ground truth and segmented volumes. All segmentation methods showed mean DSC values between 0.71-0.87 and mean SMASD values between 0.72-2.10 mm across filters. The bilateral filter with 3 mm FWHM Gaussian pre-smoothing had mean DSC 0.80 ± 0.17 and mean SMASD 1.17 ± 1.51 mm displaying approximately equal performance to a 5 mm Gaussian filter with mean DSC 0.79 ± 0.18 and mean SMASD 1.27 ± 1.52 mm. Results from models fit using GEE with a binomial distribution and exchangeable correlation structure estimated the correlation between DSC values as 0.118 and 0.290 for spheres and irregular objects, respectively. The GEE approach accounts for several factors specific to the DSC metric that simpler statistical approaches do not, providing more accurate estimations of experimental effects commonly associated with nuclear medicine segmentation studies.
Institute of Scientific and Technical Information of China (English)
Tarquinio; Mateus; Magalhães
2016-01-01
Background:Biomass regression equations are claimed to yield the most accurate biomass estimates than biomass expansion factors (BEFs). Yet, national and regional biomass estimates are general y calculated based on BEFs, especial y when using national forest inventory data. Comparison of regression equations based and BEF-based biomass estimates are scarce. Thus, this study was intended to compare these two commonly used methods for estimating tree and forest biomass with regard to errors and biases. Methods:The data were col ected in 2012 and 2014. In 2012, a two-phase sampling design was used to fit tree component biomass regression models and determine tree BEFs. In 2014, additional trees were fel ed outside sampling plots to estimate the biases associated with regression equation based and BEF-based biomass estimates;those estimates were then compared in terms of the fol owing sources of error: plot selection and variability, biomass model, model parameter estimates, and residual variability around model prediction. Results:The regression equation based below-, aboveground and whole tree biomass stocks were, approximately, 7.7, 8.5 and 8.3%larger than the BEF-based ones. For the whole tree biomass stock, the percentage of the total error attributed to first phase (random plot selection and variability) was 90 and 88%for regression-and BEF-based estimates, respectively, being the remaining attributed to biomass models (regression and BEF models, respectively). The percent bias of regression equation based and BEF-based biomass estimates for the whole tree biomass stock were−2.7 and 5.4%, respectively. The errors due to model parameter estimates, those due to residual variability around model prediction, and the percentage of the total error attributed to biomass model were larger for BEF models (than for regression models), except for stem and stem wood components. Conclusions:The regression equation based biomass stocks were found to be slightly larger
Directory of Open Access Journals (Sweden)
Tarquinio Mateus Magalhães
2015-10-01
Full Text Available Background Biomass regression equations are claimed to yield the most accurate biomass estimates than biomass expansion factors (BEFs. Yet, national and regional biomass estimates are generally calculated based on BEFs, especially when using national forest inventory data. Comparison of regression equations based and BEF-based biomass estimates are scarce. Thus, this study was intended to compare these two commonly used methods for estimating tree and forest biomass with regard to errors and biases. Methods The data were collected in 2012 and 2014. In 2012, a two-phase sampling design was used to fit tree component biomass regression models and determine tree BEFs. In 2014, additional trees were felled outside sampling plots to estimate the biases associated with regression equation based and BEF-based biomass estimates; those estimates were then compared in terms of the following sources of error: plot selection and variability, biomass model, model parameter estimates, and residual variability around model prediction. Results The regression equation based below-, aboveground and whole tree biomass stocks were, approximately, 7.7, 8.5 and 8.3 % larger than the BEF-based ones. For the whole tree biomass stock, the percentage of the total error attributed to first phase (random plot selection and variability was 90 and 88 % for regression- and BEF-based estimates, respectively, being the remaining attributed to biomass models (regression and BEF models, respectively. The percent bias of regression equation based and BEF-based biomass estimates for the whole tree biomass stock were −2.7 and 5.4 %, respectively. The errors due to model parameter estimates, those due to residual variability around model prediction, and the percentage of the total error attributed to biomass model were larger for BEF models (than for regression models, except for stem and stem wood components. Conclusions The regression equation based biomass stocks were found to
Kim, Jong Dai; Hwang, You Cheol; Ahn, Hong Yup; Park, Cheol Young
2017-09-01
Many clinical guidelines recommend apolipoprotein B (apoB) measurement, particularly in subjects with metabolic syndrome or type 2 diabetes. Recently, we developed a new equation to estimate serum apoB (apoBE). We validated the clinical relevance of apoBE and compared the performance of the equation with conventional lipid measurements and direct measurement of apoB. Study subjects were recruited from patients who visited the Health Screening Center at Kangbuk Samsung Hospital between January and December 2009 for routine medical examinations (n=78125). For analysis of coronary calcium score, we recruited study subjects from the same institution between January 2007 and December 2010 (n=16493). apoBE was significantly correlated with serum high-sensitivity C-reactive level {r=0.18 [95% confidence interval (CI), 0.18-0.19]} in partial correlation analysis adjusted for age, sex, and body mass index. apoBE was associated with a Framingham risk score indicating more than moderate risk (10-year risk ≥10%), the presence of microalbuminuria, and the presence of coronary artery calcium in multivariate logistic regression analysis. These associations were comparable to those of directly-measured serum apoB [odds ratio per 1 SD 3.02 (2.75-3.27) vs. 2.70 (2.42-3.02) for a Framingham risk score indicating more than moderate risk, 1.31 (1.21-1.41) vs. 1.35 (1.25-1.45) for the presence of microalbuminuria, and 1.33 (1.26-1.41) vs. 1.31 (1.23-1.38) for the presence of coronary calcium score respectively]. These findings were also consistently observed in subgroup analysis for subjects with type 2 diabetes. The associations between cardiovascular surrogate markers and apoBE were comparable to those of directly-measured apoB.
Directory of Open Access Journals (Sweden)
López-Moreno, J. I.
2009-12-01
Full Text Available In recent decades many authors have adopted the Penman- Monteith formula as the standard way to estimate reference evapotranspiration from climate data. The main drawback associated with the Penman-Monteith method is the relatively high data demand: temperature, solar radiation, relative humidity and wind speed are the minimum inputs required by the formula. In the Spanish Pyrenees historical databases usually consist of temperature and rainfall only, although an improvement in data acquisition is expected in terms of parameters monitored. Under situations of data scarcity, some authors recommend the use of less data intensive methods, such as the empirical Hargreaves equation. Other authors suggest that it is better to estimate the missing parameters and to apply the Penman-Monteith equation. This paper presents a study on the accuracy of the Penman-Monteith method for a situation where some parameters have to be estimated from available temperature, and wind speed data must be replaced by a constant value. The results have been compared with the information available for a location in the central Spanish Pyrenees (period 1999-2003 where parameters required by the Penman-Monteith method have been monitored. A comparison is then made with the Hargreaves model in order to assess the most appropriate method for calculation of the reference evapotranspiration. The results indicate that the use of the Penman-Monteith formula results in errors in reference evapotranspiration ETo estimation of different magnitude and sign throughout the year. However, in general, it offers a more accurate estimation of reference evapotranspiration than the Hargreaves formula.
En los últimos años, diferentes autores han adoptado el método de Penman-Monteith para estimar la evapotranspiración potencial mediante datos climáticos. El principal inconveniente de este método es que precisa de un gran número de variables para ser calculado: temperatura, radiaci
Aldoghaither, Abeer
2015-12-01
In this paper, a new method, based on the so-called modulating functions, is proposed to estimate average velocity, dispersion coefficient, and differentiation order in a space-fractional advection-dispersion equation, where the average velocity and the dispersion coefficient are space-varying. First, the average velocity and the dispersion coefficient are estimated by applying the modulating functions method, where the problem is transformed into a linear system of algebraic equations. Then, the modulating functions method combined with a Newton\\'s iteration algorithm is applied to estimate the coefficients and the differentiation order simultaneously. The local convergence of the proposed method is proved. Numerical results are presented with noisy measurements to show the effectiveness and robustness of the proposed method. It is worth mentioning that this method can be extended to general fractional partial differential equations.
Institute of Scientific and Technical Information of China (English)
ZHANG Dalin; QIU Suizheng; SU Guanghui; JIA Dounan
2007-01-01
The molten salt reactor (MSR), which is one of the generation IV reactors, can meet the demand of transmutation and breeding. The thermodynamic properties of the molten salt system like LiF-NaF-BeF2 influence the design and construction of the fuel salt and coolant in the MSR for the new generation. In this paper, the equation of state of the ternary system 15%LiF-58%NaF-27%BeF2, over the temperature range from 873.15 to 1 073.15 K at one atmosphere pressure, is described using a modified Peng-Robinson (PR) equation. The densities of the ternary system and its components are estimated by this equation directly, and compared with the experimental data. Based on the equation of state, the other thermodynamic properties such as the enthalpy, entropyand heat capacity at constant pressure are estimated by the residual function method and the fugacity coefficient method respectively. The densities calculated by PR equation are highly in agr eement with the experimental data, and the enthalpy, entropy and heat capacity evaluated by the two different methods are consistent with each other. It can be concluded that the modified PR equation can be applied to evaluate the density of the molten salt system, and it is recommended that it be used as the basis to estimate the enthalpy, entropy and heat capacity of the molten salt system.
Noort, van P.C.M.
2013-01-01
Abraham solvation equations find widespread use in environmental chemistry and pharmaco-chemistry. The coefficients in these equations, which are solvent (system) descriptors, are usually determined by fitting experimental data. To simplify the determination of these coefficients in Abraham solvatio
Evaluación de la función renal en pacientes hipertensos: subdiagnóstico de la enfermedad renal
Directory of Open Access Journals (Sweden)
Eugenia S. Sarcona
2005-01-01
Full Text Available The Evaluation of Renal Function in Hypertensive Patients: Underestimation of Renal Failure Eugenia S. Sarcona, Mónica G. Díaz Background: Hypertensive patients demonstrate a higher risk of renal failure, an independent risk factor in the development of cardiovascular disease. Serum creatinine concentration is a poor indicator as to estimate glomerular filtration rate, which leads to an underestimation of renal failure. Work objective: To compare the prevalence of renal failure among hypertensive patients by means of two different methodologies: a using the abbreviated equation taken from the “Modification of Diet in Renal Disease” (MDRDa study and b isolated serum creatinine values. Research design and methods Seven hundred and fifty-two medical records from hypertensive patients were evaluated. Glomerular filtration rate was estimated using the abbreviated equation from the MDRDa study and serum creatinine was evaluated by means of the modified Jaffé method. Results: One hundred and forty five patients (19.3% had a glomerular filtration rate less than 60 ml/min/1.73 m2 according to MDRDa. Only 33.8% of these (49 patients showed high serum creatinine, representing 6.5 % of the total of patients (p = 0.001. Age, prevalence of male sex, type 2 diabetes with proteinuria and systolic blood pressure were significantly higher in patients with renal disease. Conclusion: The present study demonstrates that the same hypertensive patients show a different prevalence of renal dysfunction according to which method was used in the evaluation. The use of MDRDa showed a prevalence of 19.3% in renal failure; however, the evaluation of isolated plasmatic creatinine concentration indicated only 6.5% of the patients presented renal failure, which clearly proves that the latter method is insufficient to evaluate renal function.
Leion, Felicia; Hegbrant, Josefine; den Bakker, Emil; Jonsson, Magnus; Abrahamson, Magnus; Nyman, Ulf; Björk, Jonas; Lindström, Veronica; Larsson, Anders; Bökenkamp, Arend; Grubb, Anders
2017-09-01
Estimating glomerular filtration rate (GFR) in adults by using the average of values obtained by a cystatin C- (eGFRcystatin C) and a creatinine-based (eGFRcreatinine) equation shows at least the same diagnostic performance as GFR estimates obtained by equations using only one of these analytes or by complex equations using both analytes. Comparison of eGFRcystatin C and eGFRcreatinine plays a pivotal role in the diagnosis of Shrunken Pore Syndrome, where low eGFRcystatin C compared to eGFRcreatinine has been associated with higher mortality in adults. The present study was undertaken to elucidate if this concept can also be applied in children. Using iohexol and inulin clearance as gold standard in 702 children, we studied the diagnostic performance of 10 creatinine-based, 5 cystatin C-based and 3 combined cystatin C-creatinine eGFR equations and compared them to the result of the average of 9 pairs of a eGFRcystatin C and a eGFRcreatinine estimate. While creatinine-based GFR estimations are unsuitable in children unless calibrated in a pediatric or mixed pediatric-adult population, cystatin C-based estimations in general performed well in children. The average of a suitable creatinine-based and a cystatin C-based equation generally displayed a better diagnostic performance than estimates obtained by equations using only one of these analytes or by complex equations using both analytes. Comparing eGFRcystatin and eGFRcreatinine may help identify pediatric patients with Shrunken Pore Syndrome.
Ribeiro-Samora, Giane A; Montemezzo, Dayane; Pereira, Danielle A G; Tagliaferri, Thaysa L; Vieira, Otávia A; Britto, Raquel R
To evaluate the agreement between the measured peak oxygen uptake (VO2peak) and the VO2peak estimated by four prediction equations based on the six-minute walk test (6MWT) in chronic heart failure patients. Thirty-six chronic heart failure patients underwent cardiopulmonary exercise testing and the 6MWT to assess their VO2peak. Four previously published equations that include the variable six-minute walk distance were used to estimate the VO2peak: Cahalin, 1996a (1); Cahalin, 1996b (2); Ross, 2010 (3); and Adedoyin, 2010 (4). The agreement between the VO2peak in the cardiopulmonary exercise testing and the estimated values was assessed using the Bland-Altman method. A p-value of <0.05 was considered statistically significant. All estimated VO2peak values presented moderate correlation (ranging from 0.55 to 0.70; p<0.001) with measured VO2peak values. Equations 2, 3, and 4 underestimated the VO2peak by 30%, 15.2%, and 51.2%, respectively, showing significant differences from the actual VO2peak measured in the cardiopulmonary exercise testing (p<0.0001 for all), and the limits of agreement were elevated. The VO2peak estimated by equation 1 was similar to that measured by the cardiopulmonary exercise testing, and despite the agreement, bias increased as VO2peak increased. Only equation 1 showed estimated VO2peak similar to the measured VO2peak; however, a large limits of agreement range (∼3 METs) does not allow its use to estimate maximal VO2peak. Copyright © 2017 Associação Brasileira de Pesquisa e Pós-Graduação em Fisioterapia. Publicado por Elsevier Editora Ltda. All rights reserved.
Westgate, Philip M
2014-05-01
Generalized estimating equations (GEE) are commonly used for the marginal analysis of correlated data, although the quadratic inference function (QIF) approach is an alternative that is increasing in popularity. This method optimally combines distinct sets of unbiased estimating equations that are based upon a working correlation structure, therefore asymptotically increasing or maintaining estimation efficiency relative to GEE. However, in finite samples, additional estimation variability arises when combining these sets of estimating equations, and therefore the QIF approach is not guaranteed to work as well as GEE. Furthermore, estimation efficiency can be improved for both analysis methods by accurate modeling of the correlation structure. Our goal is to improve parameter estimation, relative to existing methods, by simultaneously selecting a working correlation structure and choosing between GEE and two versions of the QIF approach. To do this, we propose the use of a criterion based upon the trace of the empirical covariance matrix (TECM). To make GEE and both QIF versions directly comparable for any given working correlation structure, the proposed TECM utilizes a penalty to account for the finite-sample variance inflation that can occur with either version of the QIF approach. Via a simulation study and in application to a longitudinal study, we show that penalizing the variance inflation that occurs with the QIF approach is necessary and that the proposed criterion works very well. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
McPherson, Sterling; Barbosa-Leiker, Celestina; McDonell, Michael; Howell, Donelle; Roll, John
2013-01-01
Objective A review of substance use clinical trials indicates that sub-optimal methods are the most commonly used procedures to deal with longitudinal missing information. Methods Listwise deletion (i.e., using complete cases only), positive urine analysis (UA) imputation, and multiple imputation (MI) were used to evaluate the effect of baseline substance use and buprenorphine/naloxone tapering schedule (7 or 28 days) on the probability of a positive UA (UA+) across the 4-week treatment period. Results The listwise deletion generalized estimating equations (GEE) model demonstrated that those in the 28-day taper group were less likely to submit a UA+ for opioids during the treatment period (odds ratios (OR) = 0.57, 95% confidence interval (CI): 0.39–0.83), as did the positive UA imputation model (OR = 0.43, CI: 0.34–0.55). The MI model also demonstrated a similar effect of taper group (OR = 0.57, CI: 0.42–0.77), but the effect size was more similar to that of the listwise deletion model. Conclusions Future researchers may find utilization of the MI procedure in conjunction with the common method of GEE analysis as a helpful analytic approach when the missing at random assumption is justifiable. PMID:24014144
Latcharote, P.; Leelawat, N.; Suppasri, A.; Imamura, F.
2017-02-01
The 2011 Great East Japan tsunami caused a wide range of devastating tsunami with maximum tsunami height of 40 m and 19,000 casualties especially along the Tohoku coast of Japan. The purpose of this study is to develop estimating equations of fatality ratio from tsunami arrival time for future tsunami loss assessment and investigate the effect of two coastal topography types namely, Sanriku-ria coast and Sendai plain. In this study, fatality ratio was defined as number of fatality divided by total number of people in a small scale of towns along the shoreline and tsunami arrival time was calculated from TUNAMI modelling with nesting-grids of 1350 m, 450 m, 150 m, and 50 m. Then, linear and nonlinear regression analysis were performed to develop a relationship model between fatality ratio and tsunami arrival time. Based on the results, a strong correlation that fatality ratio decreases with longer arrival time was found in both Sanriku-ria coast and Sendai plain. For different coastal types, different distributions of fatality ratio with tsunami arrival time are observed, in which fatality ratio of Sendai plain is higher than that of Sanriku ria-coast at the same arrival time generally.
GFR estimation: from physiology to public health.
Levey, Andrew S; Inker, Lesley A; Coresh, Josef
2014-05-01
Estimating glomerular filtration rate (GFR) is essential for clinical practice, research, and public health. Appropriate interpretation of estimated GFR (eGFR) requires understanding the principles of physiology, laboratory medicine, epidemiology, and biostatistics used in the development and validation of GFR estimating equations. Equations developed in diverse populations are less biased at higher GFRs than equations developed in chronic kidney disease (CKD) populations and are more appropriate for general use. Equations that include multiple endogenous filtration markers are more precise than equations including a single filtration marker. The CKD-EPI (CKD Epidemiology Collaboration) equations are the most accurate GFR estimating equations that have been evaluated in large diverse populations and are applicable for general clinical use. The 2009 CKD-EPI creatinine equation is more accurate in estimating GFR and prognosis than the 2006 MDRD (Modification of Diet in Renal Disease) Study equation and provides lower estimates of prevalence of decreased eGFR. It is useful as a "first test" for decreased eGFR and should replace the MDRD Study equation for routine reporting of serum creatinine-based eGFR by clinical laboratories. The 2012 CKD-EPI cystatin C equation is as accurate as the 2009 CKD-EPI creatinine equation in estimating GFR, does not require specification of race, and may be more accurate in patients with decreased muscle mass. The 2012 CKD-EPI creatinine-cystatin C equation is more accurate than the 2009 CKD-EPI creatinine and 2012 CKD-EPI cystatin C equations and is useful as a confirmatory test for decreased eGFR as determined by serum creatinine-based eGFR. Further improvement in GFR estimating equations will require development in more broadly representative populations, including diverse racial and ethnic groups, use of multiple filtration markers, and evaluation using statistical techniques to compare eGFR to "true GFR."
Yesilova, Abdullah; Yilmaz, Ayhan
In this study, the Poison regression, negative binomial regression and generalized estimating equations were applied to the repeated measurements based on count data obtained from the sexual behaviors of ram lambs. Negative binomial regression was more effective to handle the over dispersion that causes bias in parameter estimations in Poison regression. The generalized estimating equations were used for analyzing repeated categorical data. GEE estimates were obtained by using the exchangeable working correlation. As a result of GEE analyses, it was concluded that flehmen lip curl response, tail raising, mount duration, vocalization and weight of the ram lamb were statistically important (p<0.05) for mount frequent. However, the anogenital sniff found be not significant.
Huang, Liping; Crino, Michelle; Wu, Jason HY; Woodward, Mark; Land, Mary-Anne; McLean, Rachael; Webster, Jacqui; Enkhtungalag, Batsaikhan; Nowson, Caryl A; Elliott, Paul; Cogswell, Mary; Toft, Ulla; MILL, Jose G.; Furlanetto,Tania W.; Ilich, Jasminka Z.
2016-01-01
Background Methods based on spot urine samples (a single sample at one time-point) have been identified as a possible alternative approach to 24-hour urine samples for determining mean population salt intake. Objective The aim of this study is to identify a reliable method for estimating mean population salt intake from spot urine samples. This will be done by comparing the performance of existing equations against one other and against estimates derived from 24-hour urine samples. The effect...
Leander, Jacob; Lundh, Torbjörn; Jirstrand, Mats
2014-05-01
In this paper we consider the problem of estimating parameters in ordinary differential equations given discrete time experimental data. The impact of going from an ordinary to a stochastic differential equation setting is investigated as a tool to overcome the problem of local minima in the objective function. Using two different models, it is demonstrated that by allowing noise in the underlying model itself, the objective functions to be minimized in the parameter estimation procedures are regularized in the sense that the number of local minima is reduced and better convergence is achieved. The advantage of using stochastic differential equations is that the actual states in the model are predicted from data and this will allow the prediction to stay close to data even when the parameters in the model is incorrect. The extended Kalman filter is used as a state estimator and sensitivity equations are provided to give an accurate calculation of the gradient of the objective function. The method is illustrated using in silico data from the FitzHugh-Nagumo model for excitable media and the Lotka-Volterra predator-prey system. The proposed method performs well on the models considered, and is able to regularize the objective function in both models. This leads to parameter estimation problems with fewer local minima which can be solved by efficient gradient-based methods.
Directory of Open Access Journals (Sweden)
M. N. Mishra
2004-01-01
Full Text Available This paper is concerned with the study of the rate of convergence of the distribution of the maximum likelihood estimator of a parameter appearing linearly in the drift coefficients of two types of stochastic partial differential equations (SPDEs.
THE SOLUTION OF b的偏导-EQUATION OF （P,Q）-FORMS AND IT′ S Lp ＆ HOLDER ESTIMATES ON A STEIN MANIFOLD
Institute of Scientific and Technical Information of China (English)
WuXiaoqin
1994-01-01
By using the kernel of J. P. Demaily & Laurrent Thiebaut, the author constructs two opertors T and S which are compact and obtain the solution of b的偏导-equation of (p,q)forms and L & Holder estimates on a Stein Manifold.
Directory of Open Access Journals (Sweden)
Gerson Alves Pereira Júnior
1999-02-01
Full Text Available Apresentamos uma revisão sobre trauma renal, com ênfase na avaliação radiológica, particularmente com o uso da tomografia computadorizada, que tem se tornado o exame de eleição, ao invés da urografia excretora e arteriografia. O sucesso no tratamento conservador dos pacientes com trauma renal depende de um acurado estadiamento da extensão da lesão, classificado de acordo com a Organ Injury Scaling do Colégio Americano de Cirurgiões. O tratamento conservador não-operatório é seguro e consiste de observação contínua, repouso no leito, hidratação endovenosa adequada e antibioti- coterapia profilática, evitando-se uma exploração cirúrgica desnecessária e possível perda renal. As indicações para exploração cirúrgica imediata são abdome agudo, rápida queda do hematócrito ou lesões associadas determinadas na avaliação radiológica. Quando indicada, a exploração renal após controle vascular prévio é segura, permitindo cuidadosa inspeção do rim e sua reconstrução com sucesso, reduzindo a probabilidade de nefrectomia.We present a revision of the renal trauma with emphasis in the radiographic evaluation, particularly CT scan that it has largely replaced the excretory urogram and arteriogram in the diagnostic worh-up and management of the patient with renal trauma. The successful management of renal injuries depends upon the accurate assessment of their extent in agreement with Organ Injury Scaling classification. The conservative therapy managed by careful continuous observation, bed rest, appropriate fluid ressuscitation and prophylactic antibiotic coverage after radiographic staging for severely injured kidneys can yield favorable results and save patients from unnecessary exploration and possible renal loss. The indications for immediate exploratory laparotomy were acute abdomen, rapidly dropping hematocrit or associated injuries as determinated from radiologic evaluation. When indicated, renal exploration
Institute of Scientific and Technical Information of China (English)
吴楠
2011-01-01
Diabetic kidney disease (DKD) is the most common microvascular complications of diabetes and the main cause of chronic kidney disease and end-stage renal disease (ESRD). Because of its incidence of occult, poor prognosis and high cost, it is essential to raising awareness of DKD, making a reasonable assessment of golmerular filtration rate (GFR) and taking effective intervention to prevent disease progression as early as possible, which is also important for preventing serious complications of the kidney. Many clinicians have recognized the importance of stratifying chronic kidney disease (CKD)in diabetic subjests. This article reviews recent literature of application of equations to estimate GFR in patients with diabetes to wake a general review.%糖尿病肾脏疾病(diabetic kidney disease,DKD)是糖尿病最常见的微血管并发症,是慢性肾脏疾病及终末期肾病(end-stage renal disease,ESRD)的首因,其发病隐匿且预后不佳,治疗费用极为昂贵.提高对DKD的早期认识,对GFR进行合理性评估,早期采取有力干预手段能预防疾病恶化.目前越来越多的临床医师认识到进行慢性肾脏疾病(chronic kidney disease,CKD)分期的重要性,但目前尚未确立适合于糖尿病患者的肾小球滤过率(glomerular filtration rate,GFR)评估公式.本文回顾近年来的文献资料,就GFR估算公式在糖尿病患者中的应用做一系统综述.
... Read More Acute arterial occlusion - kidney Acute kidney failure Aneurysm Atheroembolic renal disease Blood clots Renal cell carcinoma Renal venogram X-ray Review Date 1/5/2016 Updated by: Jason Levy, ...
Renal function and symptoms/adverse effects in opioid-treated patients with cancer
DEFF Research Database (Denmark)
Kurita, G P; Lundström, S; Sjøgren, P
2015-01-01
BACKGROUND: Renal impairment and the risk of toxicity caused by accumulation of opioids and/or active metabolites is an under-investigated issue. This study aimed at analysing if symptoms/adverse effects in opioid-treated patients with cancer were associated with renal function. METHODS: Cross...... and cognitive dysfunction were assessed (EORTC QLQ-C30). Glomerular filtration rate (GFR) was estimated using Cockcroft-Gault (CG), Modification of Diet in Renal Disease (MDRD), and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI Creatinine) equations. RESULTS: Mild to severe low GFR was observed...
Deboeck, Pascal R.; Boker, Steven M.; Bergeman, C. S.
2008-01-01
Among the many methods available for modeling intraindividual time series, differential equation modeling has several advantages that make it promising for applications to psychological data. One interesting differential equation model is that of the damped linear oscillator (DLO), which can be used to model variables that have a tendency to…
The correct renal function evaluation in patients with thyroid dysfunction.
Simeoni, Mariadelina; Cerantonio, Annamaria; Pastore, Ida; Liguori, Rossella; Greco, Marta; Foti, Daniela; Gulletta, Elio; Brunetti, Antonio; Fuiano, Giorgio
2016-05-01
Thyroid dysfunction induces several renal derangements involving all nephron portions. Furthermore, dysthyroidism is a recognized risk factor associated with the development of chronic kidney disease. Current data, in fact, demonstrate that either subclinical or overt thyroid disease is associated with significant changes in creatinine, estimated glomerular filtration rate, measured glomerular filtration rate and Cystatin C. Herein, we systematically reviewed several relevant studies aiming at the identification of the most sensitive and specific parameter for the correct renal function evaluation in patients with thyroid dysfunction, that are usually treated as outpatients. Our systematic review indicates that estimated glomerular filtration rate, preferably with CKD-EPI equation, appears to be the most reliable and wieldy renal function parameter. Instead, Cystatin C should be better used in the grading of thyroid dysfunction severity.
Lin, Tai-Chia; Petrovic, Milan S; Hajaiej, Hichem; Chen, Goong
2016-01-01
The virial theorem is a nice property for the linear Schrodinger equation in atomic and molecular physics as it gives an elegant ratio between the kinetic and potential energies and is useful in assessing the quality of numerically computed eigenvalues. If the governing equation is a nonlinear Schrodinger equation with power-law nonlinearity, then a similar ratio can be obtained but there seems no way of getting any eigenvalue estimate. It is surprising as far as we are concerned that when the nonlinearity is either square-root or saturable nonlinearity (not a power-law), one can develop a virial theorem and eigenvalue estimate of nonlinear Schrodinger (NLS) equations in R2 with square-root and saturable nonlinearity, respectively. Furthermore, we show here that the eigenvalue estimate can be used to obtain the 2nd order term (which is of order $ln\\Gamma$) of the lower bound of the ground state energy as the coefficient $\\Gamma$ of the nonlinear term tends to infinity.
Yamada, Yosuke; Nishizawa, Miyuki; Uchiyama, Tomoka; Kasahara, Yasuhiro; Shindo, Mikio; Miyachi, Motohiko; Tanaka, Shigeho
2017-07-19
Background: Appendicular skeletal muscle (or lean) mass (ALM) estimated using dual-energy X-ray absorptiometry (DXA) is considered to be a preferred method for sarcopenia studies. However, DXA is expensive, has limited portability, and requires radiation exposure. Bioelectrical impedance analysis (BIA) is inexpensive, easy to use, and portable; thus BIA might be useful in sarcopenia investigations. However, a large variety of models have been commercially supplied by different companies, and for most consumer products, the equations estimating ALM are not disclosed. It is therefore difficult to use these equations for research purposes. In particular, the BIA equation is often age-dependent, which leads to fundamental difficulty in examining age-related ALM loss. The aims of the current study were as follows: (1) to develop and validate an equation to estimate ALM using multi-frequency BIA (MF-BIA) based on theoretical models, and (2) to establish sarcopenia cutoff values using the equation for the Japanese population. Methods: We measured height (Ht), weight, and ALM obtained using DXA and a standing-posture 8-electrode MF-BIA (5, 50, 250 kHz) in 756 Japanese individuals aged 18 to 86-years-old (222 men and 301 women as developing equation group and 97 men and 136 women as a cross validation group). The traditional impedance index (Ht²/Z50) and impedance ratio of high and low frequency (Z250/Z₅) of hand to foot values were calculated. Multiple regression analyses were conducted with ALM as dependent variable in men and women separately. Results: We created the following equations: ALM = (0.6947 × (Ht²/Z50)) + (-55.24 × (Z250/Z₅)) + (-10,940 × (1/Z50)) + 51.33 for men, and ALM = (0.6144 × (Ht²/Z50)) + (-36.61 × (Z250/Z₅)) + (-9332 × (1/Z50)) + 37.91 for women. Additionally, we conducted measurements in 1624 men and 1368 women aged 18 to 40 years to establish sarcopenia cutoff values in the Japanese population. The mean values minus 2 standard
Institute of Scientific and Technical Information of China (English)
Xin Wen; Shi Jin
2008-01-01
We study the L1-error estimates for the upwind scheme to the linear advection equations with a piecewise constant coefficients modeling linear waves crossing interfaces.Here the interface condition is immersed into the upwind scheme.We prove that,for initial data with a bounded variation,the numerical solution of the immersed interface upwind scheme converges in L1-norm to the differential equation with the corresponding interface condition.We derive the one-halfth order L1-error bounds with explicit coefficients following a technique used in [25].We also use some inequalities on binomial coefficients proved in a consecutive paper[32].
DEFF Research Database (Denmark)
Iolov, Alexandre; Ditlevsen, Susanne; Longtin, Andrë
2014-01-01
Analysis of sinusoidal noisy leaky integrate-and-fire models and comparison with experimental data are important to understand the neural code and neural synchronization and rhythms. In this paper, we propose two methods to estimate input parameters using interspike interval data only. One is based...... on numerical solutions of the Fokker–Planck equation, and the other is based on an integral equation, which is fulfilled by the interspike interval probability density. This generalizes previous methods tailored to stationary data to the case of time-dependent input. The main contribution is a binning method...
Smoking and renal function in people living with human immunodeficiency virus
DEFF Research Database (Denmark)
Ahlström, Magnus Glindvad; Feldt-Rasmussen, Bo; Legarth, Rebecca
2015-01-01
INTRODUCTION: Smoking is a main risk factor for morbidity and mortality in people living with human immunodeficiency virus (PLHIV), but its potential association with renal impairment remains to be established. METHODS: We did a nationwide population-based cohort study in Danish PLHIV to evaluate...... the association between smoking status and 1) overall renal function and risk of chronic kidney disease (CKD), 2) risk of any renal replacement therapy (aRRT), and 3) mortality following aRRT. We calculated estimated creatinine clearance using the Cockcroft-Gault equation (CG-CrCl), and evaluated renal function...... Cohort Study, we identified 1,475 never smokers, 768 previous smokers, and 2,272 current smokers. During study period, we observed no association of smoking status with overall renal function. Previous and current smoking was not associated with increased risk of CKD (adjusted IRR: 1.1, 95% confidence...
Asquith, William H.; Roussel, Meghan C.
2009-01-01
Annual peak-streamflow frequency estimates are needed for flood-plain management; for objective assessment of flood risk; for cost-effective design of dams, levees, and other flood-control structures; and for design of roads, bridges, and culverts. Annual peak-streamflow frequency represents the peak streamflow for nine recurrence intervals of 2, 5, 10, 25, 50, 100, 200, 250, and 500 years. Common methods for estimation of peak-streamflow frequency for ungaged or unmonitored watersheds are regression equations for each recurrence interval developed for one or more regions; such regional equations are the subject of this report. The method is based on analysis of annual peak-streamflow data from U.S. Geological Survey streamflow-gaging stations (stations). Beginning in 2007, the U.S. Geological Survey, in cooperation with the Texas Department of Transportation and in partnership with Texas Tech University, began a 3-year investigation concerning the development of regional equations to estimate annual peak-streamflow frequency for undeveloped watersheds in Texas. The investigation focuses primarily on 638 stations with 8 or more years of data from undeveloped watersheds and other criteria. The general approach is explicitly limited to the use of L-moment statistics, which are used in conjunction with a technique of multi-linear regression referred to as PRESS minimization. The approach used to develop the regional equations, which was refined during the investigation, is referred to as the 'L-moment-based, PRESS-minimized, residual-adjusted approach'. For the approach, seven unique distributions are fit to the sample L-moments of the data for each of 638 stations and trimmed means of the seven results of the distributions for each recurrence interval are used to define the station specific, peak-streamflow frequency. As a first iteration of regression, nine weighted-least-squares, PRESS-minimized, multi-linear regression equations are computed using the watershed
Xu, Peiliang
2016-01-01
The numerical integration method has been routinely used to produce global standard gravitational models from satellite tracking measurements of CHAMP/GRACE types. It is implemented by solving the differential equations of the partial derivatives of a satellite orbit with respect to the unknown harmonic coefficients under the conditions of zero initial values. From the mathematical point of view, satellite gravimetry from satellite tracking is the problem of estimating unknown parameters in the Newton's nonlinear differential equations from satellite tracking measurements. We prove that zero initial values for the partial derivatives are incorrect mathematically and not permitted physically. The numerical integration method, as currently implemented and used in satellite gravimetry and statistics, is groundless. We use three different methods to derive new local solutions to the Newton's nonlinear governing differential equations of motion with a nominal reference orbit. Bearing in mind that satellite orbits ...
Górriz Teruel, José Luis; Beltrán Catalán, Sandra
2011-12-01
Renal impairment influences the prognosis of patients with cardiovascular disease and increases cardiovascular risk. Renal dysfunction is a marker of lesions in other parts of the vascular tree and detection facilitates early identification of individuals at high risk of cardiovascular events. In patients with cardiovascular disease, renal function is assessed by measuring albuminuria in a spot urine sample and by estimating the glomerular filtration rate using creatinine-derived predictive formulas or equations. We recommend the Chronic Kidney Disease Epidemiology Collaboration or the Modification of Diet in Renal Disease formulas. The Cockcroft-Gault formula is a possible alternative. The administration of drugs that block the angiotensin-renin system can, on occasion, be associated with acute renal dysfunction or hyperkalemia. We need to know when risk of these complications exists so as to provide the best possible treatment: prevention. Given the growing number of diagnostic and therapeutic procedures in the field of cardiology that use intravenous contrast media, contrast-induced nephrotoxicity represents a significant problem. We should identify the risk factors and patients at greatest risk, and prevent it from appearing.
Liao, Fei; Zhu, Xiao-Yun; Wang, Yong-Mei; Zuo, Yu-Ping
2005-01-31
The estimation of enzyme kinetic parameters by nonlinear fitting reaction curve to the integrated Michaelis-Menten rate equation ln(S(0)/S)+(S(0)-S)/K(m)=(V(m)/K(m))xt was investigated and compared to that by fitting to (S(0)-S)/t=V(m)-K(m)x[ln(S(0)/S)/t] (Atkins GL, Nimmo IA. The reliability of Michaelis-Menten constants and maximum velocities estimated by using the integrated Michaelis-Menten equation. Biochem J 1973;135:779-84) with uricase as the model. Uricase reaction curve was simulated with random absorbance error of 0.001 at 0.075 mmol/l uric acid. Experimental reaction curve was monitored by absorbance at 293 nm. For both CV and deviation kinetic parameters and applicable for the characterization of enzyme inhibitors.
Tan, Carlos Antonio R.; Capuno, Joseph J.
2012-01-01
The treatment of drinking water is advocated to reduce the incidence of child diarrhea. However, evaluating the impact of water treatment with only observational data leads to biased estimates since it could be the occurrence of child diarrhea that induced the household to treat their drinking water. To deal with the possible simultaneity between the treatment of drinking water and the incidence of child diarrhea, we specify non-recursive two-equation causal models and apply it on a sub-sampl...
Institute of Scientific and Technical Information of China (English)
Shu-hua Zhang; Tao Lin; Yan-ping Lin; Ming Rao
2001-01-01
In this paper we will show that the Richardson extrapolation can be used to enhance the numerical solution generated by a Petrov-Galerkin finite element method for the initialvalue problem for a nonlinear Volterra integro-differential equation. As by-products, we will also show that these enhanced approximations can be used to form a class of aposteriori estimators for this Petrov-Galerkin finite element method. Numerical examples are supplied to illustrate the theoretical results.
Fast estimation from above of the maximum wave speed in the Riemann problem for the Euler equations
Guermond, Jean-Luc; Popov, Bojan
2016-09-01
This paper is concerned with the construction of a fast algorithm for computing the maximum speed of propagation in the Riemann solution for the Euler system of gas dynamics with the co-volume equation of state. The novelty in the algorithm is that it stops when a guaranteed upper bound for the maximum speed is reached with a prescribed accuracy. The convergence rate of the algorithm is cubic and the bound is guaranteed for gasses with the co-volume equation of state and the heat capacity ratio γ in the range (1 , 5 / 3 ].
Directory of Open Access Journals (Sweden)
J. Diblík
2012-01-01
Full Text Available We study a frequently investigated class of linear difference equations Δv(n=−p(nv(n−k with a positive coefficient p(n and a single delay k. Recently, it was proved that if the function p(n is bounded above by a certain function, then there exists a positive vanishing solution of the considered equation, and the upper bound was found. Here we improve this result by finding even the lower bound for the positive solution, supposing the function p(n is bounded above and below by certain functions.
Kuster, Nils; Cristol, Jean-Paul; Cavalier, Etienne; Bargnoux, Anne-Sophie; Halimi, Jean-Michel; Froissart, Marc; Piéroni, Laurence; Delanaye, Pierre
2014-01-20
The National Kidney Disease Education Program group demonstrated that MDRD equation is sensitive to creatinine measurement error, particularly at higher glomerular filtration rates. Thus, MDRD-based eGFR above 60 mL/min/1.73 m² should not be reported numerically. However, little is known about the impact of analytical error on CKD-EPI-based estimates. This study aimed at assessing the impact of analytical characteristics (bias and imprecision) of 12 enzymatic and 4 compensated Jaffe previously characterized creatinine assays on MDRD and CKD-EPI eGFR. In a simulation study, the impact of analytical error was assessed on a hospital population of 24084 patients. Ability using each assay to correctly classify patients according to chronic kidney disease (CKD) stages was evaluated. For eGFR between 60 and 90 mL/min/1.73 m², both equations were sensitive to analytical error. Compensated Jaffe assays displayed high bias in this range and led to poorer sensitivity/specificity for classification according to CKD stages than enzymatic assays. As compared to MDRD equation, CKD-EPI equation decreases impact of analytical error in creatinine measurement above 90 mL/min/1.73 m². Compensated Jaffe creatinine assays lead to important errors in eGFR and should be avoided. Accurate enzymatic assays allow estimation of eGFR until 90 mL/min/1.73 m² with MDRD and 120 mL/min/1.73 m² with CKD-EPI equation.
Institute of Scientific and Technical Information of China (English)
潘瑞蓉; 袁国跃; 叶菁菁; 杨玲; 王东; 王济芳; 陈霞; 王莹; 孙新艳; 马秋芳
2011-01-01
Objective; To investigate the application of Cockcroft-Gault(C-G) and simplified MDRD e-quations in estimating the glomerular filtration rates(GFR) in different stage renal disease. Methods; A total of 143 cases with primary or secondary chronic kidney disease were enrolled in this study. GFR by 99mTc-DTPA clearance rate was used as the reference standard. The patients were divided into four subgroups according to the GFR obtained from Gates. Group A,30 cases, GFR≥90 ml/min;group B,36 cases, 60 ml/min≤ GFR 0.05) ,rB =0.742(P 0. 05 ). The GFR [ ml · min-1· (1. 73m2) -1 ] obtained from Gates methods and MDRD equations: the correlation coefficients of four subgroups were as follows: rA=0.024 (P>0.05) ,rB=0.674 (P 0. 05). Conclusion: Cockcroft-Gault (C-G) and simplified MDRD equations were more suitable for patients with chronic kidney disease in 2,3 stage, by contrast, accuracy of CG formula was slightly better than the MDRD formula in Han nationality. Further research is needed for renal function estimation formulas in Chinese Han population.%目的:以99mTc-DTPA 同位素测定的肾小球滤过率(glomerular filtration rate,GFR)为参考标准,评估美国肾脏病基金会推荐的Cockcroft-Gault(C-G)公式与简化MDRD公式对肾功能进行分期的适用性.方法:以143 例慢性肾脏病患者为研究对象,采用肾动态显像99m Tc标记法测定GFR,根据慢性肾脏病的分期标准,将患者分成4组:A组30例,GFR≥90 ml/min;B组36例,60 ml/min≤GFR＜90 ml/min;C组47例,30 ml/min≤GFR＜60 ml/min;D组30例GFR＜30 ml/min.对各组患者分别采用CG公式、简化MDRD公式估算GFR值并用体表面积(BSA)标准化,分别与不同组BSA标准化的99mTc- DTPA 测得GFR进行比较,并进行相关性分析,评价估算公式的准确性.结果:(1) 采用肾动态显像99m Tc标记法测定的GFR与CG公式估算出的4组GFR值[单位:ml·min-1·(1.73m2)- 1]之间的相关系数为rA=-0.166 (P>0.05) ;rB =0.742(P0.05).(2)
Determination of necessary tracer mass, initial sample-collection time, and subsequent sample-collection frequency are the three most difficult aspects to estimate for a proposed tracer test prior to conducting the tracer test. To facilitate tracer-mass estimation, 33 mass-estima...
Determination of necessary tracer mass, initial sample-collection time, and subsequent sample-collection frequency are the three most difficult aspects to estimate for a proposed tracer test prior to conducting the tracer test. To facilitate tracer-mass estimation, 33 mass-estima...
Directory of Open Access Journals (Sweden)
Aynur Metin Terzibaşoğlu
2004-12-01
Full Text Available Chronic renal insufficiency is a functional definition which is characterized by irreversible and progressive decreasing in renal functions. This impairment is in collaboration with glomeruler filtration rate and serum creatinine levels. Besides this, different grades of bone metabolism disorders develop in chronic renal insufficiency. Pathologic changes in bone tissue due to loss of renal paranchyme is interrelated with calcium, phosphorus vitamine-D and parathyroid hormone. Clinically we can see high turnover bone disease, low turnover bone disease, osteomalacia, osteosclerosis and osteoporosis in renal osteodystropy. In this article we aimed to review pathology of bone metabolism disorders due to chronic renal insufficiency, clinic aspects and treatment approaches briefly.
The use of absolute values improves performance of estimation formulae
DEFF Research Database (Denmark)
Redal-Baigorri, Belén; Rasmussen, Knud; Heaf, James Goya
2013-01-01
Estimation of Glomerular Filtration Rate (GFR) by equations such as Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) or Modification of Diet in Renal Disease (MDRD) is usually expressed as a Body Surface Area (BSA) indexed value (ml/min per 1.73 m²). This can have severe clinical conse...
Directory of Open Access Journals (Sweden)
Jia-fu Feng
Full Text Available OBJECTIVE: To establish equations for the estimation of glomerular filtration rates (eGFRs based on serum creatinine (SCr and/or serum cystatin C (SCysC in Chinese patients with chronic kidney disease (CKD, and to compare the new equations with both the reference GFR (rGFR and the literature equations to evaluate their applicability. METHODS: The 788 Chinese CKD patients were randomly divided into two groups, the training group and the testing group, to establish new eGFR-formulas based on serum CysC and to validate the established formulas, respectively. (99mTc-DTPA clearance (as the rGFR, serum Cr, and serum CysC were determined for all patients, and GFR was calculated using the Cockcroft-Gault equation (eGFR1, the MDRD formula (eGFR2, the CKD-EPI formulas (eGFR3, eGFR4, and the Chinese eGFR Investigation Collaboration formulas (eGFR5, eGFR6. The accuracy of each eGFR was compared with the rGFR. RESULTS: The training and testing groups' mean GFRs were 50.84±31.36 mL/min/1.73 m(2 and 54.16±29.45 mL/min/1.73 m(2, respectively. The two newly developed eGFR formulas were fitted using iterative computation: [Formula: see text] and [Formula: see text]. Significant correlation was observed between each eGFR and the rGFR. However, proportional errors and constant errors were observed between rGFR and eGFR1, eGFR2, eGFR4, eGFR5 or eGFR6, and constant errors were observed between eGFR3 and rGFR, as revealed by the Passing & Bablok plot analysis. The Bland-Altman analysis illustrated that the 95% limits of agreement of all equations exceeded the previously accepted limits of <60 mL/min •1.73 m(2, except the equations of eGFR7 and eGFR8. CONCLUSION: The newly developed formulas, eGFR7 and eGFR8, provide precise and accurate GFR estimation using serum CysC detection alone or in combination with serum Cr detection. Differences in detection methods should be carefully considered when choosing literature eGFR equations to avoid misdiagnosis and
Energy Technology Data Exchange (ETDEWEB)
Ozcan, Zehra [University Faculty of Medicine, Nuclear Medicine Department of Ege, Bornova, Izmir (Turkey); Anderson, Peter J.; Gordon, Isky [Great Ormond Street Hospital For Children, Department of Radiology, London (United Kingdom)
2006-06-15
The two methods recommended for estimation of differential renal function (DRF) in the renography guidelines published by the European Association of Nuclear Medicine are the area under the background-subtracted time-activity curves (AUCs) (often called the integral method) and the regression slope of the background-subtracted Rutland/Patlak plot analysis. The current study investigated the agreement/disagreement of DRF estimations obtained using these two techniques. This report also focusses on the occurrence of supranormal function of the affected kidney (defined as DRF >55%) and reviews the related technical and physiological factors. A total of 394 renographic studies in 101 children with a prenatal diagnosis of unilateral renal pelvic dilatation confirmed on postnatal studies were retrieved from optical disc and reprocessed by one author. DRF was calculated using the Rutland/Patlak plot and the AUC over the time period 40-120 s following an injection of{sup 99m}Tc-mercaptoacetyltriglycine. The difference in DRF between the methods (Rutland/Patlak minus AUC) and 95% limits of agreement were calculated. The age distribution of the difference between the methods was also analysed. For all 394 measurements the mean difference was -0.8% (range -21.0% to 16.9%, SD 3.9%). The 95% limits of agreement were -7.0% to 8.6%. Analysis of the data revealed that greater spread of DRF between the techniques was seen in studies performed at a younger age: a discrepancy of >5% DRF was significantly more common in those <1 year of age than in those >1 year old (25.3% vs 9.9%; chi-square, p<0.0005). Supranormal function was found less frequently using the Rutland/Patlak method than with the AUC method (8.4% vs 11.2%; chi-square, p<0.0005). The frequency of this diagnosis was reduced to 4.6% when both methods were required to be in agreement. (orig.)
Watson, Kara M.; McHugh, Amy R.
2014-01-01
Regional regression equations were developed for estimating monthly flow-duration and monthly low-flow frequency statistics for ungaged streams in Coastal Plain and non-coastal regions of New Jersey for baseline and current land- and water-use conditions. The equations were developed to estimate 87 different streamflow statistics, which include the monthly 99-, 90-, 85-, 75-, 50-, and 25-percentile flow-durations of the minimum 1-day daily flow; the August–September 99-, 90-, and 75-percentile minimum 1-day daily flow; and the monthly 7-day, 10-year (M7D10Y) low-flow frequency. These 87 streamflow statistics were computed for 41 continuous-record streamflow-gaging stations (streamgages) with 20 or more years of record and 167 low-flow partial-record stations in New Jersey with 10 or more streamflow measurements. The regression analyses used to develop equations to estimate selected streamflow statistics were performed by testing the relation between flow-duration statistics and low-flow frequency statistics for 32 basin characteristics (physical characteristics, land use, surficial geology, and climate) at the 41 streamgages and 167 low-flow partial-record stations. The regression analyses determined drainage area, soil permeability, average April precipitation, average June precipitation, and percent storage (water bodies and wetlands) were the significant explanatory variables for estimating the selected flow-duration and low-flow frequency statistics. Streamflow estimates were computed for two land- and water-use conditions in New Jersey—land- and water-use during the baseline period of record (defined as the years a streamgage had little to no change in development and water use) and current land- and water-use conditions (1989–2008)—for each selected station using data collected through water year 2008. The baseline period of record is representative of a period when the basin was unaffected by change in development. The current period is
DEFF Research Database (Denmark)
Mocroft, A; Nielsen, Lene Ryom; Reiss, P
2014-01-01
The aim of this study was to determine whether the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI)- or Cockcroft-Gault (CG)-based estimated glomerular filtration rates (eGFRs) performs better in the cohort setting for predicting moderate/advanced chronic kidney disease (CKD) or end...
Jamie Schuler; Don C. Bragg; Kristin McElligott
2017-01-01
As southern pine forests (both planted and naturally regenerated) are more heavily used to provide biomass for the developing energy sectors and carbon sequestration, a better understanding of models used to characterize regional biomass estimates is needed. We harvested loblolly pines (Pinus taeda L.) between 0.5 and 15 cm dbh from several...
一类随机微分方程的参数估计%The Parameter Estimation for One Kind of Stochastic Differential Equations
Institute of Scientific and Technical Information of China (English)
李群
2012-01-01
随机Gilpin-Ayala方程其用幂函数的表达式来更好的刻画各种密度制约机制,具有一般代表性,本文以随机微分方程理论和统计学方法作为工具,探讨随机种群生态模型Gilpin-Ayala方程在It(o)随机积分意义下的正解存在唯一性和参数估计问题.%Stochastic Gilpin-Ayala equation is generally representative owing to use power function to better characterize the expression of various density control mechanism. So this article which is by the theory of stochastic differential equations and statistical methods discusses two points:one is existence uniqueness of positive solutions of stochastic population e-cology model;the other is parameter estimation of the model.
Perioperative acute renal failure.
LENUS (Irish Health Repository)
Mahon, Padraig
2012-02-03
PURPOSE OF REVIEW: Recent biochemical evidence increasingly implicates inflammatory mechanisms as precipitants of acute renal failure. In this review, we detail some of these pathways together with potential new therapeutic targets. RECENT FINDINGS: Neutrophil gelatinase-associated lipocalin appears to be a sensitive, specific and reliable biomarker of renal injury, which may be predictive of renal outcome in the perioperative setting. For estimation of glomerular filtration rate, cystatin C is superior to creatinine. No drug is definitively effective at preventing postoperative renal failure. Clinical trials of fenoldopam and atrial natriuretic peptide are, at best, equivocal. As with pharmacological preconditioning of the heart, volatile anaesthetic agents appear to offer a protective effect to the subsequently ischaemic kidney. SUMMARY: Although a greatly improved understanding of the pathophysiology of acute renal failure has offered even more therapeutic targets, the maintenance of intravascular euvolaemia and perfusion pressure is most effective at preventing new postoperative acute renal failure. In the future, strategies targeting renal regeneration after injury will use bone marrow-derived stem cells and growth factors such as insulin-like growth factor-1.
Renal perfusion scintigraphy; Radionuclide renal perfusion scan; Perfusion scintiscan - renal; Scintiscan - renal perfusion ... supply the kidneys. This is a condition called renal artery stenosis. Significant renal artery stenosis may be ...
Estimating glomerular filtration rate equation and medical laboratory%估算肾小球滤过率的建立与医学检验
Institute of Scientific and Technical Information of China (English)
潘柏申
2014-01-01
Estimating glomerular filtration rate is very useful in the management of chronic kidney disease.The clinical laboratories should understand these eGFR equations.%估算肾小球滤过率在慢性肾脏疾病的诊断治疗中有着重要临床意义。了解这些eGFR公式的发展和临床应用过程，可以得到一些有价值的启示。（中华检验医学杂志，2014，37：401-403）
Dalla-Betta, Peter; Schulte, Mitchell
2009-06-22
The citric acid cycle (CAC) is the central pathway of energy transfer for many organisms, and understanding the origin of this pathway may provide insight into the origins of metabolism. In order to assess the thermodynamics of this key pathway for microorganisms that inhabit a wide variety of environments, especially those found in high temperature environments, we have calculated the properties and parameters for the revised Helgeson-Kirkham-Flowers equation of state for the major components of the CAC. While a significant amount of data is not available for many of the constituents of this fundamental pathway, methods exist that allow estimation of these missing data.
Directory of Open Access Journals (Sweden)
Mitchell Schulte
2009-06-01
Full Text Available The citric acid cycle (CAC is the central pathway of energy transfer for many organisms, and understanding the origin of this pathway may provide insight into the origins of metabolism. In order to assess the thermodynamics of this key pathway for microorganisms that inhabit a wide variety of environments, especially those found in high temperature environments, we have calculated the properties and parameters for the revised Helgeson-Kirkham-Flowers equation of state for the major components of the CAC. While a significant amount of data is not available for many of the constituents of this fundamental pathway, methods exist that allow estimation of these missing data.
Catoire, Laurent; Naudet, Valérie
2004-12-01
A simple empirical equation is presented for the estimation of closed-cup flash points for pure organic liquids. Data needed for the estimation of a flash point (FP) are the normal boiling point (Teb), the standard enthalpy of vaporization at 298.15 K [ΔvapH°(298.15 K)] of the compound, and the number of carbon atoms (n) in the molecule. The bounds for this equation are: -100⩽FP(°C)⩽+200; 250⩽Teb(K)⩽650; 20⩽Δvap H°(298.15 K)/(kJ mol-1)⩽110; 1⩽n⩽21. Compared to other methods (empirical equations, structural group contribution methods, and neural network quantitative structure-property relationships), this simple equation is shown to predict accurately the flash points for a variety of compounds, whatever their chemical groups (monofunctional compounds and polyfunctional compounds) and whatever their structure (linear, branched, cyclic). The same equation is shown to be valid for hydrocarbons, organic nitrogen compounds, organic oxygen compounds, organic sulfur compounds, organic halogen compounds, and organic silicone compounds. It seems that the flash points of organic deuterium compounds, organic tin compounds, organic nickel compounds, organic phosphorus compounds, organic boron compounds, and organic germanium compounds can also be predicted accurately by this equation. A mean absolute deviation of about 3 °C, a standard deviation of about 2 °C, and a maximum absolute deviation of 10 °C are obtained when predictions are compared to experimental data for more than 600 compounds. For all these compounds, the absolute deviation is equal or lower than the reproductibility expected at a 95% confidence level for closed-cup flash point measurement. This estimation technique has its limitations concerning the polyhalogenated compounds for which the equation should be used with caution. The mean absolute deviation and maximum absolute deviation observed and the fact that the equation provides unbiaised predictions lead to the conclusion that
DEFF Research Database (Denmark)
Huang, Liping; Crino, Michelle; Wu, Jason Hy
2016-01-01
BACKGROUND: Methods based on spot urine samples (a single sample at one time-point) have been identified as a possible alternative approach to 24-hour urine samples for determining mean population salt intake. OBJECTIVE: The aim of this study is to identify a reliable method for estimating mean p...
Astolfi, Laura; Cincotti, Febo; Mattia, Donatella; Salinari, Serenella; Babiloni, Claudio; Basilisco, Alessandra; Rossini, Paolo Maria; Ding, Lei; Ni, Ying; He, Bin; Marciani, Maria Grazia; Babiloni, Fabio
2004-12-01
Different brain imaging devices are presently available to provide images of the human functional cortical activity, based on hemodynamic, metabolic or electromagnetic measurements. However, static images of brain regions activated during particular tasks do not convey the information of how these regions are interconnected. The concept of brain connectivity plays a central role in the neuroscience, and different definitions of connectivity, functional and effective, have been adopted in literature. While the functional connectivity is defined as the temporal coherence among the activities of different brain areas, the effective connectivity is defined as the simplest brain circuit that would produce the same temporal relationship as observed experimentally among cortical sites. The structural equation modeling (SEM) is the most used method to estimate effective connectivity in neuroscience, and its typical application is on data related to brain hemodynamic behavior tested by functional magnetic resonance imaging (fMRI), whereas the directed transfer function (DTF) method is a frequency-domain approach based on both a multivariate autoregressive (MVAR) modeling of time series and on the concept of Granger causality. This study presents advanced methods for the estimation of cortical connectivity by applying SEM and DTF on the cortical signals estimated from high-resolution electroencephalography (EEG) recordings, since these signals exhibit a higher spatial resolution than conventional cerebral electromagnetic measures. To estimate correctly the cortical signals, we used a subject's multicompartment head model (scalp, skull, dura mater, cortex) constructed from individual MRI, a distributed source model and a regularized linear inverse source estimates of cortical current density. Before the application of SEM and DTF methodology to the cortical waveforms estimated from high-resolution EEG data, we performed a simulation study, in which different main factors
Energy Technology Data Exchange (ETDEWEB)
Utsunomiya, Daisuke; Yanaga, Yumi; Oda, Seitaro; Namimoto, Tomohiro; Yamashita, Yasuyuki (Dept. of Diagnostic Radiology, Faculty of Life Sciences, Kumamoto Univ., Kumamoto (Japan)), email: utsunomi@kumamoto-u.ac.jp; Awai, Kazuo (Dept. of Diagnostic Radiology, Graduate School of Biomedical Sciences, Hiroshima Univ., Hiroshima (Japan)); Funama, Yoshinori (Dept. of Medical Physics, Faculty of Life Sciences, Kumamoto Univ., Kumamoto (Japan))
2011-06-15
Background Although pre-existing renal insufficiency (RI) is the most important risk factor for contrast-induced nephropathy (CIN), the background distribution of baseline renal function has not been investigated thoroughly in patients scheduled for contrast-enhanced CT. Purpose To investigate the incidence and severity of baseline RI evaluated by estimated glomerular filtration rates (eGFR) in patients who underwent contrast-enhanced CT at an academic center. Material and Methods A total of 6586 patients (3630 men and 2956 women; mean age 57.0 +- 11.9 years) who underwent contrast-enhanced CT between January and December 2008 were retrospectively studied. Of these, 829 had cardiovascular diseases (CVD), 5116 had oncologic diseases, 178 had diabetes mellitus (DM), and 1572 had chronic liver disease (CLD). The eGFR (mL/min/1.73 m2) was calculated from their serum creatinine level. Mild, moderate-a, moderate-b, and severe RI were recorded at 60 < =eGFR < 90, 45 < =eGFR < 60, 30 < =eGFR < 45 and eGFR < 30, respectively. Results Of the 6586 patients, 1.6%, 3.7%, 13.7%, and 54.2% were judged to present with severe, moderate-b, moderate-a, and mild RI, respectively. While moderate-b-to-severe RI was recorded in 133 (3.2%) of 4161 patients aged 70 years or less, it was observed in 218 (9.0%) of the 2425 patients who were 71 years or older. Among the 829 CVD patients, 9.9% manifested moderate-b-to-severe- and 73.0% mild-to-moderate-a RI. The corresponding rates were 4.4% and 68.9% for oncologic disease, 16.9% and 61.2% for DM, and 4.8% and 71.5% for CLD patients. By univariate analysis, there was a significant association between moderate-b-to-severe RI and the advanced age, CVD, DM, and non-oncologic disease. Multivariate analysis showed that the advanced age, DM, and non-oncologic disease were statistically associated with moderate-b-to-severe RI. Conclusion The incidence of RI of eGFR < 45mL/min/1.73 m2 at baseline was high in patients with advanced age, CVD and DM and
Southard, Rodney E.
2013-01-01
The weather and precipitation patterns in Missouri vary considerably from year to year. In 2008, the statewide average rainfall was 57.34 inches and in 2012, the statewide average rainfall was 30.64 inches. This variability in precipitation and resulting streamflow in Missouri underlies the necessity for water managers and users to have reliable streamflow statistics and a means to compute select statistics at ungaged locations for a better understanding of water availability. Knowledge of surface-water availability is dependent on the streamflow data that have been collected and analyzed by the U.S. Geological Survey for more than 100 years at approximately 350 streamgages throughout Missouri. The U.S. Geological Survey, in cooperation with the Missouri Department of Natural Resources, computed streamflow statistics at streamgages through the 2010 water year, defined periods of drought and defined methods to estimate streamflow statistics at ungaged locations, and developed regional regression equations to compute selected streamflow statistics at ungaged locations. Streamflow statistics and flow durations were computed for 532 streamgages in Missouri and in neighboring States of Missouri. For streamgages with more than 10 years of record, Kendall’s tau was computed to evaluate for trends in streamflow data. If trends were detected, the variable length method was used to define the period of no trend. Water years were removed from the dataset from the beginning of the record for a streamgage until no trend was detected. Low-flow frequency statistics were then computed for the entire period of record and for the period of no trend if 10 or more years of record were available for each analysis. Three methods are presented for computing selected streamflow statistics at ungaged locations. The first method uses power curve equations developed for 28 selected streams in Missouri and neighboring States that have multiple streamgages on the same streams. Statistical
Casas-Castillo, M. Carmen; Rodríguez-Solà, Raúl; Navarro, Xavier; Russo, Beniamino; Lastra, Antonio; González, Paula; Redaño, Angel
2016-11-01
The fractal behavior of extreme rainfall intensities registered between 1940 and 2012 by the Retiro Observatory of Madrid (Spain) has been examined, and a simple scaling regime ranging from 25 min to 3 days of duration has been identified. Thus, an intensity-duration-frequency (IDF) master equation of the location has been constructed in terms of the simple scaling formulation. The scaling behavior of probable maximum precipitation (PMP) for durations between 5 min and 24 h has also been verified. For the statistical estimation of the PMP, an envelope curve of the frequency factor (k m ) based on a total of 10,194 station-years of annual maximum rainfall from 258 stations in Spain has been developed. This curve could be useful to estimate suitable values of PMP at any point of the Iberian Peninsula from basic statistical parameters (mean and standard deviation) of its rainfall series.
Error Estimates for Mixed Finite Element Methods for Sobolev Equation%Sobolev方程混合有限元方法的误差估计
Institute of Scientific and Technical Information of China (English)
姜子文; 陈焕祯
2001-01-01
The purpose of this paper is to investigate the convergence of the mixed finite element method for the initial-boundary value problem for the Sobolev equation based on the Raviart-Thomas space Vh × Wh H(div; Ω) × L2(Ω). Optimal order estimates are obtained for the approximation of u, ut, the associated velocity p and divp respectively in L∞(0, T; L2(Ω)), L∞(0, T; L2(Ω)), L∞(0, T; L2(Ω)2), and L∞ (0, T; L2 (Ω)). Quasi-optimal order estimates are obtained for the approximations of u, ut in L∞(0,T;L∞(Ω)) and p in L∞(0,T;L∞(Ω)2).
Wade, Leslie; Ochsner, Evan; Lackey, Benjamin D; Farr, Benjamin F; Littenberg, Tyson B; Raymond, Vivien
2014-01-01
Advanced ground-based gravitational-wave detectors are capable of measuring tidal influences in binary neutron-star systems. In this work, we report on the statistical uncertainties in measuring tidal deformability with a full Bayesian parameter estimation implementation. We show how simultaneous measurements of chirp mass and tidal deformability can be used to constrain the neutron-star equation of state. We also study the effects of waveform modeling bias and individual instances of detector noise on these measurements. We notably find that systematic error between post-Newtonian waveform families can significantly bias the estimation of tidal parameters, thus motivating the continued development of waveform models that are more reliable at high frequencies.
Directory of Open Access Journals (Sweden)
Kesavan.E
2013-04-01
Full Text Available This paper suggests an idea to design an adaptive PID controller for Non-linear liquid tank System and is implemented in PLC. Online estimation of linear parameters (Time constant and Gain brings an exact model of the process to take perfect control action. Based on these estimated values, the controller parameters will be well tuned by internal model control. Internal model control is an unremarkably used technique and provides well tuned controller in order to have a good controlling process. PLC with its ability to have both continues control for PID Control and digital control for fault diagnosis which ascertains faults in the system and provides alerts about the status of the entire process.
Institute of Scientific and Technical Information of China (English)
Yasukazu Nakanishi; Iwao Fukui; Kazunori Kihara; Hitoshi Masuda; Satoru Kawakami; Mizuaki Sakura; Yasuhisa Fujii; Kazutaka Saito; Fumitaka Koga; Masaya Ito; Junji Yonese
2012-01-01
Anthropometric measurements,e.g.,body weight (BW),body mass index (BMI),as well as serum prostate-specific antigen (PSA) and percent-free PSA (％fPSA) have been shown to have positive correlations with total prostate volume (TPV).We developed an equation and nomegram for estimating TPV,incorporating these predictors in men with benign prostatic hyperplasia (BPH).A total of 1852 men,including 1113 at Tokyo Medical and Dental University (TMDU) Hospital as a training set and 739 at Cancer Institute Hospital (CIH) as a validation set,with PSA levels of up to 20 ng ml-1,who underwent extended prostate biopsy and were proved to have BPH,were enrolled in this study.We developed an equation for continuously coded TPV and a logistic regression-based nomngram for estimating a TPV greater than 40 ml.Predictive accuracy and performance characteristics were assessed using an area under the receiver operating characteristics curve (AUC) and calibration plots.The final linear regression model indicated age,PSA,％fPSA and BW as independent predictors of continuously coded TPV.For predictions in the training set,the multiple correlation coefficient was increased from 0.38 for PSA alone to 0.60 in the final model.We developed a novel nomogram incorporating age,PSA,％fPSA and BW for estimating TPV greater than 40 ml.External validation confirmed its predictive accuracy,with AUC value of 0.764.Calibration plots showed good agreement between predicted probability and observed proportion.In conclusion,TPV can be easily estimated using these four independent predictors.
Bollt, Erik
2012-01-01
Given multiple images that describe chaotic reaction-diffusion dynamics, parameters of a PDE model are estimated using autosynchronization, where parameters are controlled by synchronization of the model to the observed data. A two-component system of predator-prey reaction-diffusion PDEs is used with spatially dependent parameters to benchmark the methods described. Applications to modelling the ecological habitat of marine plankton blooms by nonlinear data assimilation through remote sensing is discussed.
Roth, Thomas; Freeman, Jon; Zammit, Gary; Donnelly, Patricia; Gao, Joseph; Ferreira-Cornwell, M Celeste; Gasior, Maria
2014-10-01
In a study of acute sleep deprivation in healthy male volunteers randomized to double-blind treatment with lisdexamfetamine dimesylate (20, 50, or 70 mg), placebo control, or an active control (armodafinil 250 mg), Maintenance of Wakefulness Test data were compared using a generalized estimating equation analysis to eliminate the need for unequivocal sleep latency imputation. Compared with placebo across all Maintenance of Wakefulness Tests, all active treatments were associated with lower risk of falling asleep (risk ratio [95% confidence interval]): 0.45 (0.27-0.76; P = 0.0026), 0.10 (0.05-0.20; P < 0.0001), and 0.05 (0.02-0.14; P < 0.0001) for 20, 50, and 70 mg lisdexamfetamine dimesylate, respectively, and 0.11 (0.06-0.21; P < 0.0001) for the active control. Sleep-risk ratios were similar for lisdexamfetamine dimesylate 50 or 70 mg and for the active control, but lisdexamfetamine 20 mg was associated with a greater risk of falling asleep compared with the active control (4.13 [1.97-8.67]; P = 0.0002). Generalized estimating equation analysis detected wake-promoting effects of active treatments and eliminating data imputation, suggesting model utility in future studies.
Gao, Liping
2011-01-01
This paper is concerned with the optimal error estimates and energy conservation properties of the alternating direction implicit finite-difference time-domain (ADI-FDTD) method which is a popular scheme for solving the 3D Maxwell equations. Precisely, for the case with a perfectly electric conducting (PEC) boundary condition we establish the optimal second-order error estimates in both space and time in the discrete $H^1$-norm for the ADI-FDTD scheme and prove the approximate divergence preserving property that if the divergence of the initial electric and magnetic fields are zero then the discrete $L^2$-norm of the discrete divergence of the ADI-FDTD solution is approximately zero with the second-order accuracy in both space and time. A key ingredient is two new discrete energy norms which are second-order in time perturbations of two new energy conservation laws for the Maxwell equations introduced in this paper. Furthermore, we prove that, in addition to two known discrete energy identities which are seco...
DEFF Research Database (Denmark)
Nielsen, Anita L.; Henriksen, Daniel Pilsgaard; Marinakis, Christianna;
2014-01-01
. We conclude that despite implementation of electronic prescribing and automated reporting of eGFR, patients with renal insufficiency may still be exposed to inappropriate drug use, with potential increased risk of adverse effects. Initiatives to reduce medication errors such as the use of electronic......GFR in the range of 10-49 ml/min/1.73m(2) were included. We identified 436 episodes with administration of renal risk drugs (prescribed to 183 patients): 410 drugs required dose adjustment according to the eGFR and 26 should be avoided. In total, the use or dosing of 66 (15%) of the 436 renal risk drugs...
Directory of Open Access Journals (Sweden)
Chang Hee Jung
Full Text Available BACKGROUND: Compared to the golden standard glycation index of HbA1c, glycated albumin (GA has potentials for assessing insulin secretory dysfunction and glycemic fluctuation as well as predicting diabetic vascular complications. However, the reference ranges of GA and a conversion equation need to be clearly defined. We designed this study to determine the reference ranges in patients with normal glucose tolerance (NGT based on conventional measures of glycemic status and to devise a conversion equation for calculating HbA1c and GA in a Korean population. METHODOLOGY/PRINCIPAL FINDINGS: In this multicenter, retrospective, cross-sectional study, we recruited antidiabetic drug-naïve patients with available glycemic variables including HbA1c, GA, and fasting plasma glucose regardless of glucose status. For the reference interval of serum GA, 5th to 95th percentile value of GA in subjects with NGT was adopted. The conversion equation between HbA1c and GA was devised using an estimating regression model with unknown break-points method. The reference range for GA was 9.0-14.0% in 2043 subjects. The 95th percentile responding values for FPG, and HbA1c were approximately 5.49 mmol/l, and 5.6%, respectively. The significant glycemic turning points were 5.868% HbA1c and 12.2% GA. The proposed conversion equation for below and above the turning point were GA (% = 6.960+0.8963 × HbA1c (% and GA (% = -9.609+3.720 × HbA1c (%, respectively. CONCLUSIONS/SIGNIFICANCE: These results should be helpful in future studies on the clinical implications of high GA relative to HbA1c and the clinical implementation of diabetes management.
Directory of Open Access Journals (Sweden)
José Jordão Filho
2011-11-01
Full Text Available The study was conducted to estimate requirements of energy and crude protein for maintenance, weight gain and egg production of Japanese quails in the period of 67 to 107 days of age. Two experiments were performed: one, to determine the requirements for maintenance of protein, and the other, for energy. Experiments were conducted in a completely randomized design with four dietary levels of offer and four replicates of six birds. The diets offered were: ad libitum (100%, 75%, 50%, and 25% consumption ad libitum (below maintenance. The methodology used to estimate the demand for maintenance was the comparative slaughter. For estimation of the requirement for weight gain, eight groups of 15 quails were reared separately, fed ad libitum and housed under 22 ºC controlled temperature. From these poultry, three groups were slaughtered at 5, 10, 15, 20, 25, 30, 35 and 40 days of the trial. The requirement for egg production was obtained by taking the ratio of energy content, egg protein, efficiency of energy use and protein for egg production. Prediction equations that estimate maintenance requirement, weight gain and egg production in energy and crude protein of Japanese quail include: metabolizable energy (kcal/bird/day = 92.34*body weight0.75 + 6.23*weight gain + 4.19*egg mass; crude protein (g/bird/day = 6.71*body weight0.75 + 0.615*weight gain + 0.258*egg mass.
Hanlon, Joseph T; Wang, Xiaoqiang; Handler, Steven M; Weisbord, Steven; Pugh, Mary Jo; Semla, Todd; Stone, Roslyn A; Aspinall, Sherrie L
2011-06-01
Inappropriate prescribing of primarily renally cleared medications in older patients with kidney disease can lead to adverse outcomes. To estimate the prevalence of potentially inappropriate prescribing of 21 primarily renally cleared medications based on 2 separate estimates of renal function and to identify factors associated with this form of suboptimal prescribing in older VA nursing home (NH) patients. Longitudinal study Participants were 1304 patients, aged 65 years or older, admitted between January 1, 2004, and June 30, 2005, for 90 days or more to 1 of 133 VA NHs. Potentially inappropriate prescribing of primarily renally cleared medications determined by estimating creatinine clearance using the Cockcroft Gault (CG) and Modification of Diet in Renal Disease (MDRD) equations and applying explicit guidelines for contraindicated medications and dosing. The median estimated creatinine clearance via CG was 67 mL/min, whereas it was 80 mL/min/1.73m(2) with the MDRD. Overall, 11.89% patients via CG and only 5.98% via MDRD had evidence of potentially inappropriate prescribing of at least 1 renally cleared medication. The most commonly involved medications were ranitidine, glyburide, gabapentin, and nitrofurantoin. Factors associated with potentially inappropriate prescribing as per the CG were age older than 85 (adjusted odds ratio [AOR] 4.24, 95% confidence interval [CI] 2.42-7.43), obesity (AOR 0.26, 95% CI 0.14-0.50) and having multiple comorbidities (AOR 1.09 for each unit increase in the Charlson comorbidity index, 95% CI 1.01-1.19). Potentially inappropriate prescribing of renally cleared medications is common in older VA NH patients. Intervention studies to improve the prescribing of primarily renally cleared medications in nursing homes are needed. Copyright © 2011 American Medical Directors Association. Published by Elsevier Inc. All rights reserved.
Ferreira, João Pedro; Girerd, Nicolas; Pellicori, Pierpaolo; Duarte, Kevin; Girerd, Sophie; Pfeffer, Marc A; McMurray, John J V; Pitt, Bertram; Dickstein, Kenneth; Jacobs, Lotte; Staessen, Jan A; Butler, Javed; Latini, Roberto; Masson, Serge; Mebazaa, Alexandre; Rocca, Hans Peter Brunner-La; Delles, Christian; Heymans, Stephane; Sattar, Naveed; Jukema, J Wouter; Cleland, John G; Zannad, Faiez; Rossignol, Patrick
2016-11-10
Renal impairment is a major risk factor for mortality in various populations. Three formulas are frequently used to assess both glomerular filtration rate (eGFR) or creatinine clearance (CrCl) and mortality prediction: body surface area adjusted-Cockcroft-Gault (CG-BSA), Modification of Diet in Renal Disease Study (MDRD4), and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation. The CKD-EPI is the most accurate eGFR estimator as compared to a "gold-standard"; however, which of the latter is the best formula to assess prognosis remains to be clarified. This study aimed to compare the prognostic value of these formulas in predicting the risk of cardiovascular mortality (CVM) in population-based, cardiovascular risk, heart failure (HF) and post-myocardial infarction (MI) cohorts. Two previously published cohorts of pooled patient data derived from the partners involved in the HOMAGE-consortium and from four clinical trials - CAPRICORN, EPHESUS, OPTIMAAL and VALIANT - the high risk MI initiative, were used. A total of 54,111 patients were included in the present analysis: 2644 from population-based cohorts; 20,895 from cardiovascular risk cohorts; 1801 from heart failure cohorts; and 28,771 from post-myocardial infarction cohorts. Participants were patients enrolled in the respective cohorts and trials. The primary outcome was CVM. All formulas were strongly and independently associated with CVM. Lower eGFR/CrCl was associated with increasing CVM rates for values below 60 mL/min/m(2). Categorical renal function stages diverged in a more pronounced manner with the CG-BSA formula in all populations (higher χ(2) values), with lower stages showing stronger associations. The discriminative improvement driven by the CG-BSA formula was superior to that of MDRD4 and CKD-EPI, but remained low overall (increase in C-index ranging from 0.5 to 2 %) while not statistically significant in population-based cohorts. The integrated discrimination improvement and
老年人肾功能测定方法的评价%Evaluation of Applicability of Renal Function Estimating Methods in Elderly Patients
Institute of Scientific and Technical Information of China (English)
孟瑚
2012-01-01
对于老年人,精确地评估肾小球滤过率对明确慢性肾脏病、早期实施保护肾功能的治疗、并给予正确的药物剂量至关重要.临床常用的评估肾功能的方法 有血清肌酐、内生肌酐清除率,根据CG公式或MDRD公式估算肾小球滤过率,血清胱抑素C和放射性核素法,还有近年出现的基于血清胱抑素C的估算公式.这些方法 在老年人群中的应用各有不足之处.临床需根据实际条件和对诊断精确度的要求,选择合适的方法.%Accurate glomerular filtration rate measurement is important for identification of chronic renal disease which may allow early implementation of renoprotective therapy and proper medication dosing among elderly individuals. Current detection methods consist of serum creatinine concentration, endogenous creati-nine clearance ratea,ccording to CG formula or MDRD formula estimate glomerular filtration rate,serum cys-tatin C concentration,radioisotopic methods,and the formula based on cystatin C. Each of them has inadequacy in elderly population. In clinical practice, it is necessary to choose a suitable methods according to available armamentarium and requirement.
Danchin, Raphaël; Xu, Jiang
2016-11-01
The global existence issue for the isentropic compressible Navier-Stokes equations in the critical regularity framework was addressed in Danchin (Invent Math 141(3):579-614, 2000) more than 15 years ago. However, whether (optimal) time-decay rates could be shown in critical spaces has remained an open question. Here we give a positive answer to that issue not only in the L 2 critical framework of Danchin (Invent Math 141(3):579-614, 2000) but also in the general L p critical framework of Charve and Danchin (Arch Ration Mech Anal 198(1):233-271, 2010), Chen et al. (Commun Pure Appl Math 63(9):1173-1224, 2010), Haspot (Arch Ration Mech Anal 202(2):427-460, 2011): we show that under a mild additional decay assumption that is satisfied if, for example, the low frequencies of the initial data are in {L^{p/2}({R}d)} , the L p norm (the slightly stronger {dot B^0_{p,1}} norm in fact) of the critical global solutions decays like {t^{-d(1/p-1/4)}} for {tto+∞,} exactly as firstly observed by Matsumura and Nishida in (Proc Jpn Acad Ser A 55:337-342, 1979) in the case p = 2 and d = 3, for solutions with high Sobolev regularity. Our method relies on refined time weighted inequalities in the Fourier space, and is likely to be effective for other hyperbolic/parabolic systems that are encountered in fluid mechanics or mathematical physics.
Directory of Open Access Journals (Sweden)
A. V. Govorov
2012-01-01
Full Text Available Renal cryoablation is an alternative minimally-invasive method of treatment for localized renal cell carcinoma. The main advantages of this methodology include visualization of the tumor and the forming of "ice ball" in real time, fewer complications compared with other methods of treatment of renal cell carcinoma, as well as the possibility of conducting cryotherapy in patients with concomitant pathology. Compared with other ablative technologies cryoablation has a low rate of repeat sessions and good intermediate oncological results. The studies of long-term oncological and functional results of renal cryoablation are presently under way.
DEFF Research Database (Denmark)
Holm-Nielsen, P; Sørensen, Flemming Brandt
1988-01-01
lesion. Three cases of renal angiomyolipoma, 2 of which underwent perfusion-fixation, were studied by electron microscopy to clarify the cellular composition of this lesion. In the smooth muscle cells abundant accumulation of glycogen was found, whereas the lipocytes disclosed normal ultrastructural......-specific vesicular structures. These findings suggest a secondary vascular damage, i.e. the thickened vessels may not be a primary, integral part of renal angiomyolipoma. Evidence of a common precursor cell of renal angiomyolipoma was not disclosed. It is concluded that renal angiomyolipoma is a hamartoma composed...
Hippisley-Cox, Julia; Coupland, Carol
2015-11-11
Is it possible to develop and externally validate risk prediction equations to estimate the 10 year risk of blindness and lower limb amputation in patients with diabetes aged 25-84 years? This was a prospective cohort study using routinely collected data from general practices in England contributing to the QResearch and Clinical Practice Research Datalink (CPRD) databases during the study period 1998-2014. The equations were developed using 763 QResearch practices (n=454,575 patients with diabetes) and validated in 254 different QResearch practices (n=142,419) and 357 CPRD practices (n=206,050). Cox proportional hazards models were used to derive separate risk equations for blindness and amputation in men and women that could be evaluated at 10 years. Measures of calibration and discrimination were calculated in the two validation cohorts. Risk prediction equations to quantify absolute risk of blindness and amputation in men and women with diabetes have been developed and externally validated. In the QResearch derivation cohort, 4822 new cases of lower limb amputation and 8063 new cases of blindness occurred during follow-up. The risk equations were well calibrated in both validation cohorts. Discrimination was good in men in the external CPRD cohort for amputation (D statistic 1.69, Harrell's C statistic 0.77) and blindness (D statistic 1.40, Harrell's C statistic 0.73), with similar results in women and in the QResearch validation cohort. The algorithms are based on variables that patients are likely to know or that are routinely recorded in general practice computer systems. They can be used to identify patients at high risk for prevention or further assessment. Limitations include lack of formally adjudicated outcomes, information bias, and missing data. Patients with type 1 or type 2 diabetes are at increased risk of blindness and amputation but generally do not have accurate assessments of the magnitude of their individual risks. The new algorithms calculate
Coupland, Carol
2015-01-01
Study question Is it possible to develop and externally validate risk prediction equations to estimate the 10 year risk of blindness and lower limb amputation in patients with diabetes aged 25-84 years? Methods This was a prospective cohort study using routinely collected data from general practices in England contributing to the QResearch and Clinical Practice Research Datalink (CPRD) databases during the study period 1998-2014. The equations were developed using 763 QResearch practices (n=454 575 patients with diabetes) and validated in 254 different QResearch practices (n=142 419) and 357 CPRD practices (n=206 050). Cox proportional hazards models were used to derive separate risk equations for blindness and amputation in men and women that could be evaluated at 10 years. Measures of calibration and discrimination were calculated in the two validation cohorts. Study answer and limitations Risk prediction equations to quantify absolute risk of blindness and amputation in men and women with diabetes have been developed and externally validated. In the QResearch derivation cohort, 4822 new cases of lower limb amputation and 8063 new cases of blindness occurred during follow-up. The risk equations were well calibrated in both validation cohorts. Discrimination was good in men in the external CPRD cohort for amputation (D statistic 1.69, Harrell’s C statistic 0.77) and blindness (D statistic 1.40, Harrell’s C statistic 0.73), with similar results in women and in the QResearch validation cohort. The algorithms are based on variables that patients are likely to know or that are routinely recorded in general practice computer systems. They can be used to identify patients at high risk for prevention or further assessment. Limitations include lack of formally adjudicated outcomes, information bias, and missing data. What this study adds Patients with type 1 or type 2 diabetes are at increased risk of blindness and amputation but generally do not have accurate
随机微分方程解的二次型估计%Quadratic Estimation to Solution of Stochastic Differential Equations
Institute of Scientific and Technical Information of China (English)
马洪强; 胡良剑
2011-01-01
由于随机微分方程(SDE)的解析解求解困难,所以推导SDE解的不等式估计式是十分必要的.在随机系统的稳定性分析和控制设计中,李亚普诺夫函数常常采用二次型函数.本文把SDE解的传统的欧几里德范数形式估计式推广到SDE解的二次型估计式,包括解的矩估计和几乎必然估计.我们分别在加权线性增长条件和加权单边增长条件下给出了二次型矩估计式以及样本李亚普诺夫指数的上界表达式.%Since most stochastic differential equations (SDE) are not explicitly solvable, it is very important to find the estimation of the solution in the form of inequalities. In the research on stability analysis and control design of the stochastic systems, Lyapunov functions often take the quadratic forms. The aim of this paper is to extend the estimation from the classical Euclidean form to the quadratic form, including moment estimation and almost surely estimation of the SDE solution. As the results, the upper limits of moment estimation and sample Lyapunov index in quadratic function of solution are given under weighted linear growth condition and weighted one-side growth condition, respectively.
Xue, Hongqi; Wu, Hulin; 10.1214/09-AOS784
2010-01-01
This article considers estimation of constant and time-varying coefficients in nonlinear ordinary differential equation (ODE) models where analytic closed-form solutions are not available. The numerical solution-based nonlinear least squares (NLS) estimator is investigated in this study. A numerical algorithm such as the Runge--Kutta method is used to approximate the ODE solution. The asymptotic properties are established for the proposed estimators considering both numerical error and measurement error. The B-spline is used to approximate the time-varying coefficients, and the corresponding asymptotic theories in this case are investigated under the framework of the sieve approach. Our results show that if the maximum step size of the $p$-order numerical algorithm goes to zero at a rate faster than $n^{-1/(p\\wedge4)}$, the numerical error is negligible compared to the measurement error. This result provides a theoretical guidance in selection of the step size for numerical evaluations of ODEs. Moreover, we h...
Directory of Open Access Journals (Sweden)
A. Yakubu
2014-10-01
Full Text Available The study was aimed to develop prediction models using stepwise multiple linear regressionanalysis for estimating the body condition score (BCS from the body weight (BW, testicular length(TL, testicular diameter (TD and scrotal circumference (SC of indigenous Yankasa rams. Data wereobtained from 120 randomly selected rams with approximately two and half years of age, from differentextensively managed herds in Nasarawa State, Nigeria. Although pairwise phenotypic correlationsindicated strong association (P<0.01 among the measured variables, there was collinearity problembetween BW and SC as revealed by the variance inflation factors (VIF and tolerance valves (T. TheVIT was higher than 10 (VIF = 19.45 and 16.65 for BW and SC, respectively. The Twas smaller than0.1 (T = 0.05 and 0.06 in BW and SC, respectively. BW was retained among the collinear variables, andwas singly accounted for 83.7% of the variation in BCS. However, a slight improvement was obtainedfrom the prediction of BCS from BW and TL [coefficient of determination (R2, adjusted R2 and rootmean squares error (RMSE were 85.3%, 85.1% and 0.305, respectively]. The prediction of the BCS ofYankasa rams from BW and testicular measurements could therefore be a potential tool for sustainableproduction and improvement of small ruminants in Nigeria.
Corgna, Enrichetta; Betti, Maura; Gatta, Gemma; Roila, Fausto; De Mulder, Pieter H. M.
2007-01-01
In Europe, renal cancer (that is neoplasia of the kidney, renal pelvis or ureter (ICD-9 189 and ICD-10 C64-C66)) ranks as the seventh most common malignancy in men amongst whom there are 29,600 new cases each year (3.5% of all cancers). Tobacco, obesity and a diet poor in vegetables are all acknowle
Institute of Scientific and Technical Information of China (English)
1992-01-01
920705 Endothelin and acute renal failure:study on their relationship and possiblemechanisms. LIN Shanyan(林善锬), et al.Renal Res Lab, Huashan Hosp, Shanghai MedUniv, Shanghai, 200040. Natl Med J China 1992;72(4): 201-205. In order to investigate the role of endothelin
Corgna, E.; Betti, M.; Gatta, G.; Roila, F.; Mulder, P.H.M. de
2007-01-01
In Europe, renal cancer (that is neoplasia of the kidney, renal pelvis or ureter (ICD-9 189 and ICD-10 C64-C66)) ranks as the seventh most common malignancy in men amongst whom there are 29,600 new cases each year (3.5% of all cancers). Tobacco, obesity and a diet poor in vegetables are all
Corgna, Enrichetta; Betti, Maura; Gatta, Gemma; Roila, Fausto; De Mulder, Pieter H. M.
2007-01-01
In Europe, renal cancer (that is neoplasia of the kidney, renal pelvis or ureter (ICD-9 189 and ICD-10 C64-C66)) ranks as the seventh most common malignancy in men amongst whom there are 29,600 new cases each year (3.5% of all cancers). Tobacco, obesity and a diet poor in vegetables are all
Directory of Open Access Journals (Sweden)
D. García Moreno
2013-08-01
Full Text Available On 8 November 1983 an earthquake of magnitude 4.6 damaged more than 16 000 buildings in the region of Liège (Belgium. The extraordinary damage produced by this earthquake, considering its moderate magnitude, is extremely well documented, giving the opportunity to compare the consequences of a recent moderate earthquake in a typical old city of Western Europe with scenarios obtained by combining strong ground motions and vulnerability modelling. The present study compares 0.3 s spectral accelerations estimated from ground motion prediction equations typically used in Western Europe with those obtained locally by applying the statistical distribution of damaged masonry buildings to two fragility curves, one derived from the HAZUS programme of FEMA (FEMA, 1999 and another developed for high-vulnerability buildings by Lang and Bachmann (2004, and to a method proposed by Faccioli et al. (1999 relating the seismic vulnerability of buildings to the damage and ground motions. The results of this comparison reveal good agreement between maxima spectral accelerations calculated from these vulnerability and fragility curves and those predicted from attenuation law equations, suggesting peak ground accelerations for the epicentral area of the 1983 earthquake of 0.13–0.20 g (g: gravitational acceleration.
Is the new GFR equation using inulin clearance a more accurate method for Asian patients?
Kim, Beom Seok; Lee, Yong Kyu; Choi, Hoon Young; Choi, Seung Ok; Shin, Sug Kyun; Ha, Sung Kyu; Lee, Kang Wook; Kim, Yang Wook; Kim, Yong Lim; Yasuda, Yoshinari; Imai, Enyu; Horio, Masaru; Tomino, Yasuhiko; Matsuo, Seiichi; Lee, Ho Yung
2015-12-01
Recently, a new glomerular filtration rate (GFR) equation for the Japanese population was proposed using measured inulin clearance. To expand its applicability to other Asian populations, we performed a comparative study in the Korean population. Inulin clearance was measured in 166 patients from seven participating medical centers in Korea. Patient's sera and urine were collected, and baseline clinical characteristics were measured to provide an estimated GFR (eGFR) by the Japanese GFR equation using inulin clearance (Japanese-GFR equation), the Modification of Diet in Renal Disease (MDRD) study equation, and the Chronic Kidney Disease - Epidemiology Collaboration (CKD-EPI) equation. We compared the results to determine which equation best estimated the measured GFR (mGFR). Accuracy (95% CI) within 30% of mGFR by the Japanese-GFR equation, the CKD-EPI equation and the MDRD study equation were 66 (58 - 72), 51 (43 - 58), and 55 (47 - 62)%, respectively. Bias (mGFR minus eGFR) were 3.4 ± 22.4, -12.0 ± 22.1, and -9.7 ± 23.8 mL/min/1.73 m2, respectively. The accuracy of the Japanese-GFR equation was significantly better than MDRD study equation in subjects with mGFR < 60 mL/min/1.73 m2 and in total subjects. The bias of the Japanese-GFR equation was significantly smaller compared with other two equations in total subjects. The Japanese-GFR equation has a higher accuracy with less bias than the other equations in estimating GFR in Korean populations. Further studies are required to determine if the current Japanese-GFR equation could represent the standard eGFR for other Asian populations.
Cozzi, Denis A; Ceccanti, Silvia; Frediani, Simone; Mele, Ermelinda; Cozzi, Francesco
2013-09-01
Mild-to-moderate renal function loss may be an independent risk factor for cardiovascular disease and overall mortality. As in adults with renal carcinoma nephrectomy is associated with an high risk for moderate renal function loss, we aimed to assess the renal function adaptation over a long period of time in children with unilateral renal tumor (URT). Seventy-two children who underwent surgery for URT were enrolled in this study. Glomerular filtration rate was estimated (eGFR) with the Modification of Diet in Renal Study or the Schwartz equation, as appropriate for the age. Twelve patients treated by nephron-sparing surgery (Group A) and 42 treated by nephrectomy (Group B) had an age between 2 and 30 years; 18 patients treated by nephrectomy had an age between 33 and 51 years (Group C). At cross-sectional follow-up 8% patients of Group A, 42% of Group B and 78% of Group C presented a mild-to-moderate renal function. The longitudinal data stratified by post-operative intervals showed that patients of Group C presented a significant progressive decrease in mean ± standard deviation eGFR (88.1 ± 22.6 during the third decade after surgery vs. 66.6 ± 15.6 ml/min/1.73 m(2) during the fifth decade after surgery; P = 0.02). The longitudinal data stratified by age showed that patients with an age between 45 and 54 years presented a mean eGFR significantly lower than that expected for the physiological renal function decline with aging (P = 0.001). Aging is associated with a mild-to-moderate renal function loss in many adult patients following nephrectomy during childhood for URT. Copyright © 2013 Wiley Periodicals, Inc.
DEFF Research Database (Denmark)
Holtkamp, Frank A; de Zeeuw, Dick; Thomas, Merlin C
2011-01-01
Intervention in the renin-angiotensin-aldosterone-system (RAAS) is associated with slowing the progressive loss of renal function. During initiation of therapy, however, there may be an acute fall in glomerular filtration rate (GFR). We tested whether this initial fall in GFR reflects a renal hem......GFR, during losartan treatment, the slower the rate of long-term eGFR decline. Hence, interpretation of trial results relying on slope-based GFR outcomes should separate the initial drug-induced GFR change from the subsequent long-term effect on GFR....
Dyslipoproteinemia in renal transplantation.
Directory of Open Access Journals (Sweden)
Gunjotikar R
1994-01-01
Full Text Available Twenty-seven live related donor renal allograft recipients were evaluated for dyslipoproteinemia. Twenty-two patients received dual immunosuppression with prednisolone and azathioprine. Five patients received cyclosporin as well. Total cholesterol (Tch, triglycerides (TG, HDL cholesterol (HDLch, LDL cholesterol (LDLch and VLDL cholesterol (VLDLch levels were estimated. Fifteen (56% patients showed significant lipoprotein abnormalities. Renal allograft recipients showed significantly lower levels of Tch (p < 0.05 and LDLch (p < 0.05 and higher levels of TG (p < 0.005 and HDLch (p < 0.05. Diet and beta blockers did not influence lipoprotein levels. A significant negative correlation was noted between post-transplant duration and Tch, TG and VLDLch levels. Increased TG levels were associated with increase in weight and higher daily prednisolone dosage at the time of evaluation. The study confirms the existence of dyslipoproteinemia in renal allograft recipients.
Estimates for Eigenvalues for a five Order Differential Equation%一类5阶常微分方程特征值的估计
Institute of Scientific and Technical Information of China (English)
吴平
2014-01-01
考虑一类常微分方程的特征值的估计，利用分部积分、Rayleigh定理和不等式估计等方法，获得了用前n个特征值来估计第n＋1个特征值的上界的不等式，其估计系数与区间的几何度量无关，其结果在物理学和力学等领域中应用广泛。%This paper considers the estimates for eigenvalues of a differential equation .We construct some test function and then use the Rayleigh theorem to obtain a basic inequality .These estimates are that the (n+1)th eigenvalues is bounded from above by an amount depending on the first n eigenvalues and being independent of the measure of the domain in which the problem is concerned .This kind of problem is signifi-cant is potential application to mechanics and physics .
Morgan, Thomas M; Jones, Deborah P; Cooper, William O
2014-09-01
In utero exposure to certain drugs early in pregnancy may adversely affect nephrogenesis. Exposure to drugs later in pregnancy may affect the renin-angiotensin system, which could have an impact on fetal or neonatal renal function. Reduction in nephron number and renal function could have adverse consequences for the child several years later. Data are limited on the information needed to guide decisions for patients and providers regarding the use of certain drugs in pregnancy. The study of drug nephroteratogenicity has not been systematized, a large, standardized, global approach is needed to evaluate the renal risks of in utero drug exposures.
Glomerular filtration rate in cows estimated by a prediction formula.
Murayama, Isao; Miyano, Anna; Sato, Tsubasa; Iwama, Ryosuke; Satoh, Hiroshi; Ichijyo, Toshihiro; Sato, Shigeru; Furuhama, Kazuhisa
2014-12-01
To testify the relevance of Jacobsson's equation for estimating bovine glomerular filtration rate (GFR), we prepared an integrated formula based on its equation using clinically healthy dairy (n=99) and beef (n=63) cows, and cows with reduced renal function (n=15). The isotonic, nonionic, contrast medium iodixanol was utilized as a test tracer. The GFR values estimated from the integrated formula were well consistent with those from the standard multisample method in each cow strain, and the Holstein equation prepared by a single blood sample in Holstein dairy cows. The basal reference GFR value in healthy dairy cows was significantly higher than that in healthy beef cows, presumably due to a breed difference or physiological state difference. It is concluded that the validity for the application of Jacobsson's equation to estimate bovine GFR is proven and it can be used in bovine practices.