Simple Quadratic Model Research Articles

Auto-correcting for atmospheric effects in thermal hyperspectral measurements

Correct estimation of soil and vegetation thermal emissivities is of huge importance in remote sensing studies. It has been shown that the emissivity of leaves retrieved from field observations show subtle spectral features that are related to leaf water content. However, such field measurements provide additional challenges before leaf water content can be successfully obtained, specifically atmospheric correction. The aim of this research was to investigate how information within hyperspectral thermal observations can be used to auto-correct the atmospheric influence. Hyperspectral thermal measurements were taken over a large variety of soil and vegetation types (including vineyard and barley) during ESA’s REFLEX campaign in 2012 using a MIDAC FTIR radiometer. Using MODTRAN simulations, a simple quadratic model was constructed that emulates the atmosphere radiative transfer between the target and the sensor. Afterwards, this model was used to estimate the concentrations of H20 (g) and CO2 (g) while simultaneously correcting for these gas absorptions. Finally, a temperature-emissivity separation was applied to estimate the emissivities of the different land surface components.The uncertainty of the approach was evaluated by comparing the retrieved gas concentrations against parallel measurements of a LICOR 7500. It was found that most measurements of gas concentrations were successfully retrieved, with uncertainties lower than 25%. However, absolute correction of the absorption features proved more difficult and resulted in overestimations of the correction-terms. This was mainly due to overlapping of spectral features with the observations in the simulations that proved troublesome.

Prediction of the margin of victory only from team rankings for regular season games in NCAA men’s basketball

The main objective of this article was to investigate the extent to which the margin of victory can be predicted solely by the rankings of the opposing teams in NCAA Division I men’s basketball games. Several past studies have modeled this relationship for the games played during the March Madness tournament. This work aimed at verifying whether the models advocated in previous studies can accurately predict the margin of victory in regular season games. Indeed, most previous articles have shown that a simple quadratic regression model provides fairly accurate predictions of the margin of victory when team rankings only range from 1 to 16. Does that still hold true when team rankings increase to 351? Do the model assumptions hold? Can semi- or nonparametric methods that yield even better results (i.e. predicted margins of victory that more closely resemble actual results) be found? The analyses presented in this article suggest that the answer is “yes” to all three questions!

PH gradients in the diffusive boundary layer of subarctic macrophytes

Highly productive macrophytes produce diurnal and seasonal cycles in CO2 concentrations modulated by metabolic activity, which cause discrepancies between pH in the bulk water and near seaweed blades, especially when entering the diffusion boundary layer (DBL). Calcifying epiphytic organisms living in this environment are therefore exposed to a different pH environment than that of the water column. To evaluate the actual pH environment on blade surfaces, we measured the thickness of the DBL and pH gradients within it for six subarctic macrophytes: Fucus vesiculosus, Ascophyllum nodosum, Ulva lactuca, Zostera marina, Saccharina longicruris, and Agarum clathratum. We measured pH under laboratory conditions at ambient temperatures (2–3 °C) and slow, stable flow over the blade surface at five light intensities (dark, 30, 50, 100 and 200 µmol photons m−2 s−1). Boundary layer thickness ranged between 511 and 1632 µm, while the maximum difference in pH (∆pH) between the blade surface and the water column ranged between 0.4 ± 0.14 (average ± SE; Zostera) and 1.2 ± 0.13 (average ± SE; Ulva) pH units. These differences in pH are larger than predictions for pH changes in the bulk water by the end of the century. A simple quadratic model best described the relationship between light intensity and maximum ∆pH, pointing at relatively low optimum PAR of between 28 and 139 µmol photons m−2 s−1 to reach maximum ∆pH. Elevated pH at the blade surface may provide chemical “refugia” for calcifying epiphytic organisms, especially during summer at higher latitudes where photoperiods are long.

Synthesis of hydroxyapatite nanorods for application in water defluoridation and optimization of process variables: Advantage of ultrasonication with precipitation method over conventional method

This research work presents the synthesis of hydroxyapatite (Hap) nanorods for defluoridation of drinking water by using both conventional (CM) and ultrasonication with precipitation (USPM) methods. Calcium nitrate was reacted with potassium phosphate in presence of ammonia for controlled pH to synthesize Hap nanorods, which was characterized using FTIR, XRD, SEM, TG-DTA, and TEM/EDS for determining its phase composition, structural and thermal decomposition behavior. When USPM method was used for synthesis, the yield of the Hap nanorods was improved from 83.24±1.0% to 90.2±1.0%, and complete phase transformation occurred with formation of elongated Hap nanorods. Effects of process parameters such as solution pH, contact time and adsorbent dose were studied through response surface methodology (RSM). A simple quadratic model was developed using Central Composite Design (CCD) and optimum parameters for fluoride adsorption process were determined to be pH 7, contact time 3h and adsorbent dose 7g/L for maximum removal capacity. Fluoride removal efficiency was predicted to be 93.64% which was very close to the experimental value obtained at 92.86% using ultrasonically prepared Hap. Fluoride adsorption isotherms fitted the Freundlich isotherm with an adsorption capacity of 1.49mg/g, while the kinetic studies revealed that the process followed pseudo-second order model. The treated water quality parameters such as residual fluoride, calcium leached, total hardness and alkalinity was investigated, and it was observed that all these parameters were within the permissible limits as per WHO and BIS standards.

Fluoride adsorption by doped and un-doped magnetic ferrites CuCexFe2-xO4: Preparation, characterization, optimization and modeling for effectual remediation technologies

A series of doped and un-doped magnetic adsorbents CuCexFe2-xO4 (x=0.0–0.5) for fluoride were prepared with the micro-emulsion method. Fluoride adsorption was optimized for solution pH, temperature, contact time, and initial concentration and was monitored via normal phase ion chromatography (IC). The effect of concomitant anions was also explored to perform and simulate competitive fluoride adsorption in real water samples. Optimal adsorption was discovered by a simple quadratic model based on central composite design (CCD) and the response surface method (RSM). The adsorption, electrochemical and magnetic properties were compared between doped and un-doped ferrites. Doped ferrites (x=0.1–0.5) were found to be superior to un-doped ferrites (x=0) regarding the active sites, functional groups and fluoride adsorption. The characterization, optimization and application results of the doped ferrites indicated enhanced fluoride adsorption and easy separation with a simple magnet.

Relation between Lyapunov exponents and decoherence for real scalar fields in de Sitter spacetime

We investigate the relationship between orbital instability and decoherence in de Sitter (dS) spacetime. We consider a simple quadratic toy model proposed by Brandenberger, Laflamme and Miji\ifmmode \acute{c}\else \'{c}\fi{} of two interacting scalar fields in a dS background. It admits a modewise separation, with each mode consisting of a pair of nonautonomous coupled harmonic oscillators. We show that the (classical) maximal Lyapunov exponent of every mode equals the asymptotic rate of (quantum) von Neumann entropy production of each oscillator, assuming an initial vacuum. We find that for moderately long times after horizon crossing, orbital instability, entropy and single-mode squeezing are larger for increasing coupling strength. If the entropy of an oscillator increases more rapidly than squeezing, for example in the strong-coupling regime for not too high frequencies, the noise of every quadrature of the asymptotic state will be larger than the vacuum noise. The results suggest the possibility that simple, nonlinear interacting physical processes with unstable or chaotic classical counterparts may provide an important contribution to the effectiveness of the classicalization of cosmological scalar fields during a dS stage of spacetime expansion.

A comparison of Evolutionary Operation and Simplex for process improvement

Two sequential improvement methods, Evolutionary Operation (EVOP) and Simplex, are compared in a computer simulation study. The EVOP procedure uses underlying statistical models, while the Simplex procedure is based on heuristical rules. On a simple quadratic model the effect of dimensionality, perturbation size – called factorstep in this research – and noise-level on both methods is investigated. Simplex performs quite well in cases with a low level of noise but becomes very unreliable in cases of higher noise and small factorsteps. EVOP is more robust against noise, most noticeable in higher dimensions, but the number of measurements for every step becomes prohibitive with increasing dimensionality.

Modeling and optimization of equivalent plastic strain in equal-channel angular rolling using response surface methodology

The mechanical properties of metallic strips can be improved by producing an ultra-fine-grained microstructure. The equal-channel angular rolling process is a severe plastic deformation technique suitable for such a purpose. In this article, the effect of the equal-channel angular rolling parameters on the equivalent plastic strain is investigated and their optimum values are reported. The analysis is focused on the following parameters: thickness ratio ( K), die channel angle ( ϕ), die outer corner angle ( ψ), fillet radius ( r), friction coefficient between strip and rolls ( µ), and friction factor between strip and die ( m). Using a combination of the finite element modeling and the response surface methodology with central composite design, a simple and efficient quadratic model is developed to predict the equivalent plastic strain dependence on the equal-channel angular rolling process parameters. The analysis of variance is applied to assess the validity of the model and find the significant parameters. The results show that the die channel angle is the most significant parameter, while the friction coefficient between strip and rolls has no considerable effect on equivalent plastic strain. Moreover, the following optimum values of the parameters are obtained: K = 0.96, ϕ = 90.10°, ψ = 21.21°, r = 2.31 mm, µ = 0.20, and m = 0.19. An increase of about 14.86% in the equivalent plastic strain can be achieved by adopting these values for the process parameters.

Estimation of a Nonlinear Intervention Phase Trajectory for Multiple-Baseline Design Data

A multilevel logistic model for estimating a nonlinear trajectory in a multiple-baseline design is introduced. The model is applied to data from a real multiple-baseline design study to demonstrate interpretation of relevant parameters. A simple change-in-levels (ΔLevels) model and a model involving a quadratic function (Quadratic) for the nonlinear intervention phase data were also estimated. In addition, a simulation study was conducted to assess Markov chain Monte Carlo estimation of the logistic model and compare its trajectory recovery with use of the ΔLevels and Quadratic models. While most of the logistic model's parameter values were recovered well, trajectory recovery was very reasonable using the simpler Quadratic model. Results are discussed along with recommendations for practitioners and directions for future research.

LASS: A Simple Assignment Model with Laplacian Smoothing

We consider the problem of learning soft assignments of N items to K categories given two sources of information: an item-category similarity matrix, which encourages items to be assigned to categories they are similar to (and to not be assigned to categories they are dissimilar to), and an item-item similarity matrix, which encourages similar items to have similar assignments. We propose a simple quadratic programming model that captures this intuition. We give necessary conditions for its solution to be unique, define an out-of-sample mapping, and derive a simple, effective training algorithm based on the alternating direction method of multipliers. The model predicts reasonable assignments from even a few similarity values, and can be seen as a generalization of semisupervised learning. It is particularly useful when items naturally belong to multiple categories, as for example when annotating documents with keywords or pictures with tags, with partially tagged items, or when the categories have complex interrelations (e.g. hierarchical) that are unknown.

A nonmonotone trust region method based on simple quadratic models

In this paper, a new nonmonotone trust region algorithm with simple quadratic models is proposed. Unlike traditional nonmonotone trust region method, our trust region subproblem is very simple by using a new scale approximation of the minimizing function’s Hessian. The global convergence of the proposed algorithm is established under some reasonable conditions. Numerical tests on a set of large scale standard test problems are presented and show that the new algorithm is efficient and robust.

A simple method of dating marine growth circuli on scales of wild one sea-winter and two sea-winter Atlantic salmon (Salmo salar)

A method of dating the marine growth circuli on Atlantic salmon (Salmo salar L.) scales is presented. Data were available for 54 salmon, intercepted as smolts at the completion of their downstream migration in the River North Esk, Scotland. Smolts were tagged, released, and recaptured as return adults after either one (1SW) or two (2SW) winters at sea. Dating of circuli was achieved by fitting a simple quadratic model to the circuli pertaining to fixed points on the scale. For 1SW fish, the latter were the dates of river emigration and completion of marine migration, and the midpoint circulus (equal to the winter solstice) of the winter annulus. For 2SW salmon, these were the date of emigration and the two winter annulus midpoints. A key assumption is that winter annulus formation arises from constraints of light availability on foraging, and hence, reduced growth rate. Comparative analyses indicate the method to be robust and effectively transferable to salmon of known capture date — but of unknown smolt emigration date — by assuming a fixed date of emigration; in such cases, circuli could still be allocated with confidence to a calendar month.

Trends and projections of annual birth volumes in the State of Qatar: 1970–2025

Background: The ethnic profile of Qatar is a combination of its indigenous peoples (Qataris) and non-resident foreigners (non-Qataris). Its population has increased dramatically during the last 30 years to around 1.9 m (although only 15% are Qataris) leading to an increase in the number of local births. A recent unexpected surge in births has lead to a need to re-evaluate the trends in birth numbers and develop more reliable predictions for both near- (2015) and far-term (2025) annual numbers of births to support the many healthcare planning initiatives which are currently underway. Methods: There is considerable information already available in Qatar which can facilitate such a study. This paper collates these various data, charts and investigates their visible trends and develops a simple mathematical model which projects the annual number of births which might reasonably be expected to emerge later in this decade and beyond. Results: The Qatari sub-population has maintained a reliable linear increase in birth numbers since data first began to be collected. The births among the non-GCC and Asian sub-populations are the primary cause of the recent nonlinear increase which can be well-described in the near-term by a simple quadratic curve. Far-term projections require a non-linear mathematical model which combines the regular linear increase among the Qataris with an exponentially decreasing demand for “in-Qatar” births from the non-Qataris. The trend for multiple births in Qatar (i.e. the annual number of live-born twins, triplets etc.) has shown significant increases during the last 20 years but may be reaching a plateau. Among Qataris the numbers have been higher but – at least for triplets and higher-order births – this gap has decreased in the last few years. It appears that the increase in multiple births has been associated with the current expansion of IVF programs and other forms of assisted conception in Qatar. Conclusions: The annual number of births in Qatar has recently shown a significant departure from its previous trend, requiring a radical reassessment of future projections. There has also been a concomitant increase in multiple births which has been associated with the expansion of IVF programs and other forms of assisted conception. A simple quadratic model predicts that there will be ∼22,500 births in 2015, of which ∼8,000 will be Qatari. A far-term projection for 2025 suggests that this number is likely to rise to ∼27,000 but with some small additional increase yet to come.

Critical ages in the life course of the adult brain: nonlinear subcortical aging

Age-related changes in brain structure result from a complex interplay among various neurobiological processes, which may contribute to more complex trajectories than what can be described by simple linear or quadratic models. We used a nonparametric smoothing spline approach to delineate cross-sectionally estimated age trajectories of the volume of 17 neuroanatomic structures in 1100 healthy adults (18–94 years). Accelerated estimated decline in advanced age characterized some structures, for example hippocampus, but was not the norm. For most areas, 1 or 2 critical ages were identified, characterized by changes in the estimated rate of change. One-year follow-up data from 142 healthy older adults (60–91 years) confirmed the existence of estimated change from the cross-sectional analyses for all areas except 1 (caudate). The cross-sectional and the longitudinal analyses agreed well on the rank order of age effects on specific brain structures (Spearman ρ = 0.91). The main conclusions are that most brain structures do not follow a simple path throughout adult life and that accelerated decline in high age is not the norm of healthy brain aging.

Utility of Normal Tissue-to-Tumor α/β Ratio When Evaluating Isodoses of Isoeffective Radiation Therapy Treatment Plans

To achieve a better understanding of the effect of the number of fractions on normal tissue sparing for equivalent tumor control in radiation therapy plans by using equivalent biologically effective dose (BED) isoeffect calculations.The simple linear quadratic (LQ) model was assumed to be valid up to 10 Gy per fraction. Using the model, we formulated a well-known mathematical equality for the tumor prescription dose and probed and solved a second mathematical problem for normal tissue isoeffect. That is, for a given arbitrary relative isodose distribution (treatment plan in percentages), 2 isoeffective tumor treatment regimens (N fractions of the dose D and n fractions of the dose d) were denoted, which resulted in the same BED (corresponding to 100% prescription isodose). Given these situations, the LQ model was further exploited to mathematically establish a unique relative isodose level, z (%), for the same arbitrary treatment plan, where the BED to normal tissues was also isoeffective for both fractionation regimens.For the previously stated problem, the relative isodose level z (%), where the BEDs to the normal tissue were also equal, was defined by the normal tissue α/β ratio divided by the tumor α/β times 100%. Fewer fractions offers a therapeutic advantage for those portions of the normal tissue located outside the isodose surface, z, whereas more fractions offer a therapeutic advantage for those portions of the normal tissue within the isodose surface, z.Relative isodose-based treatment plan evaluations may be useful for comparing isoeffective tumor regimens in terms of normal tissue effects. Regions of tissues that would benefit from hypofractionation or standard fractionation can be identified.

Fluence map optimization (FMO) with dose–volume constraints in IMRT using the geometric distance sorting method

A new heuristic algorithm based on the so-called geometric distance sorting technique is proposed for solving the fluence map optimization with dose–volume constraints which is one of the most essential tasks for inverse planning in IMRT. The framework of the proposed method is basically an iterative process which begins with a simple linear constrained quadratic optimization model without considering any dose–volume constraints, and then the dose constraints for the voxels violating the dose–volume constraints are gradually added into the quadratic optimization model step by step until all the dose–volume constraints are satisfied. In each iteration step, an interior point method is adopted to solve each new linear constrained quadratic programming. For choosing the proper candidate voxels for the current dose constraint adding, a so-called geometric distance defined in the transformed standard quadratic form of the fluence map optimization model was used to guide the selection of the voxels. The new geometric distance sorting technique can mostly reduce the unexpected increase of the objective function value caused inevitably by the constraint adding. It can be regarded as an upgrading to the traditional dose sorting technique. The geometry explanation for the proposed method is also given and a proposition is proved to support our heuristic idea. In addition, a smart constraint adding/deleting strategy is designed to ensure a stable iteration convergence. The new algorithm is tested on four cases including head–neck, a prostate, a lung and an oropharyngeal, and compared with the algorithm based on the traditional dose sorting technique. Experimental results showed that the proposed method is more suitable for guiding the selection of new constraints than the traditional dose sorting method, especially for the cases whose target regions are in non-convex shapes. It is a more efficient optimization technique to some extent for choosing constraints than the dose sorting method. By integrating a smart constraint adding/deleting scheme within the iteration framework, the new technique builds up an improved algorithm for solving the fluence map optimization with dose–volume constraints.

Modulated reheating by a curvaton

There might be a light scalar field during inflation which is not responsible for the accelerating inflationary expansion. Then, its quantum fluctuation is stretched during inflation. This scalar field could be a curvaton, if it decays at a late time. In addition, if the inflaton decay rate depends on the light scalar field expectation value by interactions between them, density perturbations could be generated by the quantum fluctuation of the light field when the inflaton decays. This is a modulated reheating mechanism. We study curvature perturbation in models where a light scalar field does not only play a role of curvaton but also induce modulated reheating at the inflaton decay. We calculate the nonlinearity parameters as well as the scalar spectral index and the tensor-to-scalar ratio. We find that there is a parameter region where nonlinearity parameters are also significantly enhanced by the cancellation between the modulated effect and the curvaton contribution. For the simple quadratic potential model of both inflaton and curvaton, both tensor-to-scalar ratio and nonlinearity parameters could be simultaneously large.

A new nonmonotone adaptive trust region method based on simple quadratic models

Based on simple quadratic models of the trust region subproblem, we combine the trust region method with the nonmonotone and adaptive techniques to propose a new nonmonotone adaptive trust region algorithm for unconstrained optimization. Unlike traditional trust region method, our trust region subproblem is very simple by using a new scale approximation of the minimizing function’s Hessian. The new method needs less memory capacitance and computational complexity. The convergence results of the method are proved under certain conditions. Numerical results show that the new method is effective and attractive for large scale unconstrained problems.

Subthreshold characteristics of ballistic electron emission spectra

We report upon a comprehensive investigation of the subthreshold characteristics of the ballistic electron emission microscopy (BEEM) current in ballistic electron emission spectroscopy. Starting from the Bell-Kaiser model, we derive an analytical equation to describe the subthreshold behavior of the BEEM current. It is found that the BEEM current in this region should exhibit a subthreshold swing of ∼60 mV/decade at room temperature, which we experimentally verified. This finding provides a rule of thumb for the detectability of the subthreshold behavior in a spectrum. For spectra where the subthreshold behavior is discernible above the signal noise, it is demonstrated that significant deviations in the near-threshold region can occur when fitting with a simple quadratic model that ignores the subthreshold behavior. To take the subthreshold behavior into account, a simple analytical model is proposed. This model not only fits significantly better in the near threshold region than the square model, but also gives a barrier height closer to the one extracted from the Bell-Kaiser model. More significantly, this model provides a quick method to estimate the subthreshold BEEM current amplitude based on the BEEM current above the barrier height.

THE RISE TIME OF NORMAL AND SUBLUMINOUS TYPE Ia SUPERNOVAE

We calculate the average stretch-corrected rise-time of type Ia supernovae (SNe Ia) in the Supernova Legacy Survey. We use the aggregate lightcurves of spectroscopic and photometrically identified SNe Ia to fit the rising part of the lightcurve with a simple quadratic model. We obtain a lightcurve shape corrected, i .e. stretch-corrected, fiducial rise-time of 17.02^{+0.18}_{-0.28} (stat) days. The measured rise-time differs from an earlier finding by the SNLS (Conley et al. 2006) due to the use of different SN Ia templates. We compare it to nearby samples using the same methods and find no evolution in the early part of the lightcurve of SNe Ia up to z=1. We search for variations among different populations, particularly subluminous objects, by dividing the sample in stretch. Bright and slow decliners (s>1.0) have consistent stretch-corrected rise-times compared to fainter and faster decliners (0.8<s<1.0); they are shorter by 0.57^{+0.47}_{-0.50} (stat) days. Subluminous SNe Ia (here defined as objects with s<0.8), although less constrained, are also consistent, with a rise-time of 18.03^{+0.81}_{-1.37} (stat) days. We study several systematic biases and find that the use of different fiducial templates may affect the average rise-time but not the intrinsic differences between populations. Based on our results, we estimate that subluminous SNe Ia are powered by 0.05-0.35 solar masses of radioactive nickel synthesized in the explosion. Our conclusions are the same for the single-stretch and two-stretch parameterizations of the lightcurve.