Value Of Fit Research Articles

Methodological notes on model comparisons and strategy classification: A falsificationist proposition

AbstractTaking a falsificationist perspective, the present paper identifies two major shortcomings of existing approaches to comparative model evaluations in general and strategy classifications in particular. These are (1) failure to consider systematic error and (2) neglect of global model fit. Using adherence measures to evaluate competing models implicitly makes the unrealistic assumption that the error associated with the model predictions is entirely random. By means of simple schematic examples, we show that failure to discriminate between systematic and random error seriously undermines this approach to model evaluation. Second, approaches that treat random versus systematic error appropriately usually rely on relative model fit to infer which model or strategy most likely generated the data. However, the model comparatively yielding the best fit may still be invalid. We demonstrate that taking for granted the vital requirement that a model by itself should adequately describe the data can easily lead to flawed conclusions. Thus, prior to considering the relative discrepancy of competing models, it is necessary to assess their absolute fit and thus, again, attempt falsification. Finally, the scientific value of model fit is discussed from a broader perspective.

Advanced material modelling in numerical simulation of primary acetabular press-fit cup stability

Primary stability of artificial acetabular cups, used for total hip arthroplasty, is required for the subsequent osteointegration and good long-term clinical results of the implant. Although closed-cell polymer foams represent an adequate bone substitute in experimental studies investigating primary stability, correct numerical modelling of this material depends on the parameter selection. Material parameters necessary for crushable foam plasticity behaviour were originated from numerical simulations matched with experimental tests of the polymethacrylimide raw material. Experimental primary stability tests of acetabular press-fit cups consisting of static shell assembly with consecutively pull-out and lever-out testing were subsequently simulated using finite element analysis. Identified and optimised parameters allowed the accurate numerical reproduction of the raw material tests. Correlation between experimental tests and the numerical simulation of primary implant stability depended on the value of interference fit. However, the validated material model provides the opportunity for subsequent parametric numerical studies.

Mechanical Analysis and Evaluation of Compulsator

Compulsator is the best pulse power supply of electromagnetic gun, into which the energy storage, electromechanical energy conversion, and pulse shaping are integrated. Due to the unique machine configuration, nature of pulse power generation, and potentially large impulse forces and torques, the mechanical analysis of compulsator is essential and different from that of the traditional electrical machine. Based on the iron-core and air-core prototypes, mechanical analysis of iron-core and air-core compulsators was presented in this paper. Although the mechanical analysis theoretical bases of iron-core and air-core compulsator topologies are the same, the analysis processes are different. In the iron-core passive compulsator, the compensation conductive shield was assembled by a thermal shrink fit. The compensation conductive shield would be separated from the rotor as the rotating speed increased above critical speed. Therefore, the critical speed and reasonable value of interference fit were calculated. In the air-core passive compulsator, the compensation aluminum shield was epoxy bonded to the carbon fiber banding, because the elevated temperature about a few hundred degrees centigrade of thermal shrink fit requirement would result in a breakdown of carbon fiber epoxy resin banding. The bonding strength was evaluated, then the reasonable epoxy resin system was chosen, and safe layer thickness was calculated. Due to the large discharge pulse current, the pulsed tangential and radial forces applied to the rotor and armature windings in the stator were also analyzed for iron-core and air-core compulsators. The prototypes operated safely and smoothly, and the design and calculation results were validated.

Defining brand values through sponsorship

PurposeThe purpose of this paper is to consider sponsorship embedded within a brand strategy and how fit between the sponsor's and the sponsored brand provides a platform for the integrated communication of brand values. The importance of a service dimension to the brand in the form of retail outlets is considered.Design/methodology/approachA case study research strategy was adopted. Other methods were used in the building of data and the triangulation of the findings: documentary analysis and participant observation also provided valuable insights. In particular, the environment in which the case study strategy was adopted demanded an understanding of the discourse on which the relationship was built and developed.FindingsExplains how the company integrated the sponsorship relationship within its communications and placed the relationship at the centre of its redefined brand strategy. The close semantic fit between the sponsoring and sponsored organisation helped to facilitate a co‐branding relationship and the service dimension of the brand provided an opportunity for a comparatively rapid redefinition of brand values.Practical implicationsDevelops an understanding of the methods by which sponsoring organisations may successfully meet corporate objectives. The findings show the considerable value of semantic fit if deployed appropriately.Originality/valueThis paper conceptually structured the research outcomes within the context of existing research relating to the two issues of brand strategy and semantic fit.

The fit of home to foreign market environment: An exploratory study of the relationship of congruence to performance

This research draws on the foreign market entry and organizational strategy literatures to address the relationship between home and foreign market environmental congruence and overseas venture performance. Theoretical arguments from prior studies have been juxtaposed in that transaction cost and diversification perspectives hypothesize different outcomes of firm entry into heterogeneous or homogeneous market environments. Using polynomial regression we test hypotheses regarding the home and overseas environmental congruence–venture performance relationship, and the organizational factors which act as moderators of this relationship. The results show that traditional transaction cost and market replication theories fail to fully explain the value of environmental fit when matching overseas market with domestic market profiles. Furthermore, the findings reveal that the moderating effects of organizational factors on the market congruence–venture performance relationship are also counter-intuitive to traditional perspectives. Managerial implications, study limitations, and directions for future research are offered.

On the relation between the photoactivation energy and the absorbance spectrum of visual pigments

We relate the collected experimental data on the minimum energy for photoactivation ( E a) to the wavelengths of peak absorbance ( λ max) of 12 visual pigments. The E a values have been determined from the temperature-dependence of spectral sensitivity in the long-wavelength range. As shown previously, the simple physical idea E a=const.×(1/ λ max) (here termed the Stiles–Lewis–Barlow or SLB relation) does not hold strictly. Yet there is a significant correlation between E a and 1/λ max (r 2=0.73) and the regression slope obtained by an unbiased fit is 84% of the predicted value of the best SLB fit. The correlation can be decomposed into effects of A1→A2 chromophore change and effects of opsin differences. For a chromophore change in the same opsin, studied in two A1/A2 pigment pairs, the SLB relation holds nearly perfectly. In seven pigments having different opsins but the same (A2) chromophore, the correlation of E a and 1/ λ max remained highly significant ( r 2=0.87), but the regression coefficient is only 72% of the best SLB fit. We conclude that (1) when the chromophore is exchanged in the same opsin, the λ max shift directly reflects the difference in photoactivation energies, (2) when the opsin is modified by amino acid substitutions, λ max and E a can be tuned partly independently, although there is a dominant tendency for inverse proportionality. In four (A1) rhodopsins with virtually the same λ max, E a varied over a 4.5 kcal/mol range, which may be taken as a measure of the freedom for independent tuning. Assuming that low E a correlates with high thermal noise, we suggest that the leeway in λ max− E a coupling is used by natural selection to keep E a as high as possible in long-wavelength-sensitive pigments, and that this is why the opsin-dependent E a(1/ λ max)-relation is shallower than predicted.

On the relation between the photoactivation energy and the absorbance spectrum of visual pigments

We relate the collected experimental data on the minimum energy for photoactivation ( E a ) to the wavelengths of peak absorbance ( λ max ) of 12 visual pigments. The E a values have been determined from the temperature-dependence of spectral sensitivity in the long-wavelength range. As shown previously, the simple physical idea E a =const.×(1/ λ max ) (here termed the Stiles–Lewis–Barlow or SLB relation) does not hold strictly. Yet there is a significant correlation between E a and 1/λ max (r 2 =0.73) and the regression slope obtained by an unbiased fit is 84% of the predicted value of the best SLB fit. The correlation can be decomposed into effects of A1→A2 chromophore change and effects of opsin differences. For a chromophore change in the same opsin, studied in two A1/A2 pigment pairs, the SLB relation holds nearly perfectly. In seven pigments having different opsins but the same (A2) chromophore, the correlation of E a and 1/ λ max remained highly significant ( r 2 =0.87), but the regression coefficient is only 72% of the best SLB fit. We conclude that (1) when the chromophore is exchanged in the same opsin, the λ max shift directly reflects the difference in photoactivation energies, (2) when the opsin is modified by amino acid substitutions, λ max and E a can be tuned partly independently, although there is a dominant tendency for inverse proportionality. In four (A1) rhodopsins with virtually the same λ max , E a varied over a 4.5 kcal/mol range, which may be taken as a measure of the freedom for independent tuning. Assuming that low E a correlates with high thermal noise, we suggest that the leeway in λ max − E a coupling is used by natural selection to keep E a as high as possible in long-wavelength-sensitive pigments, and that this is why the opsin-dependent E a (1/ λ max )-relation is shallower than predicted.

Intracranial vessel segmentation from time-of-flight MRA using pre-processing of the MIP Z-buffer: accuracy of the ZBS algorithm

We evaluate the accuracy of a vascular segmentation algorithm which uses continuity in the maximum intensity projection (MIP) depth Z-buffer as a pre-processing step to generate a list of 3D seed points for further segmentation. We refer to the algorithm as Z-buffer segmentation (ZBS). The pre-processing of the MIP Z-buffer is based on smoothness measured using the minimum χ 2 value of a least square fit. Points in the Z-buffer with χ 2 values below a selected threshold are used as seed points for 3D region growing. The ZBS algorithm couples spatial continuity information with intensity information to create a simple yet accurate segmentation algorithm. We examine the dependence of the segmentation on various parameters of the algorithm. Performance is assessed in terms of the inclusion/exclusion of vessel/background voxels in the segmentation of intracranial time-of-flight MRA images. The evaluation is based on 490,256 voxels from 14 patients which were classified by an observer. ZBS performance was compared to simple thresholding and to segmentation based on vessel enhancement filtering. The ZBS segmentation was only weakly dependent on the parameters of the initial MIP image generation, indicating the robustness of this approach. Region growing based on Z-buffer generated seeds was advantageous compared to simple thresholding. The ZBS algorithm provided segmentation accuracies similar to that obtained with the vessel enhancement filter. The ZBS performance was notably better than the filter based segmentation for aneurysms where the assumptions of the filter were violated. As currently implemented the algorithm slightly under-segments the intracranial vasculature.

Joint toxicity of similarly and dissimilarly acting chemicals to Daphnia magna at different response levels.

The toxicity of two amines, nonylamine and decylamine, which have a narcotic effect on organisms, and ethylparathion (enzymatic inhibitor) on Daphnia magna has been studied when acting singly and in joint toxicity tests. This was done on the basis of an isobologram method where curves of constant response, i.e., isoboles are plotted vs. the concentrations of the two toxicants. The concentrations that immobilized 50, 10, and 0% of the test population in 48 h (IC50-48h, IC10-48h, and IC0-48h) were calculated. It is shown that nonylamine-decylamine mixtures follow a near concentration addition model of joint toxicity, while ethylparathion-decylamine mixtures follow a less than additive or near independent action model. The study was performed using three toxicity indices: additive index, sum of toxic units, and similarity parameter lambda. An analysis of the similarity parameter lambda is done to evaluate whether it has a constant value for IC50-48h, IC10-48h, and IC0-48h. The results suggest that it is quite probable that a constant value of lambda can be used to characterize all response levels, as the isoboles corresponding to the average value of the similarity parameter fit within the 95% confidence intervals of toxicant concentrations at all response levels. The average value of lambda is about 0.80 for the nonylamine-decylamine test and 0.30 for the ethylparathion-decylamine test.

Limited possibility for quantifying mean particle size by logarithmic light-scattering spectroscopy.

Recent studies have shown that the slope of logarithmic scattering spectroscopy of a turbid medium is related to the sizes of the scattering particles within the turbid medium. Mie theory can be used to generate a logarithmic plot of the reduced-scattering coefficient versus wavelength. According to Nilsson et al. [Appl. Opt. 37, 1256 (1998)], the slope value of a linear fit of the logarithmic scattering spectroscopy between 600 and 1050 nm can be used for direct determination of particle size. We performed similar calculations using the Rayleigh-Gans approximation and obtained an analogous overall shape with additional sinusoidal features. Our calculations indicate a possible relationship between the slope and the particle size when the size is used to calculate the slope, namely, in the forward calculation. However, because of the sinusoidal pattern, the inverse calculation to obtain the particle size from the slope may be applied only for particles with a radius of <0.13 microm in combination with 650-1050-nm light. Caution should be exercised when inverse calculation is performed to determine the scattering particle sizes in the range of radii >0.13 microm, with the slope of logarithmic scattering spectroscopy within 650-1050 nm.

Person–Organisation Fit: The Match Between Theory and Methodology: Introduction to the Special Issue

In this introduction to a special issue on Person–Organisation Fit it is argued that future studies on P–O fit should pay more attention to criteria of variability and the value of fit for selecting the components of the fit measure. Moreover, more within‐person designs should be used in order to examine processes of adaptation and to improve the power of P–O fit research.

Aftershock occurrence rate decay properties for intermediate and deep earthquake sequences

We perform a detailed analysis of seven aftershock sequences with intermediate- or deep-focus mainshocks occurring in the Aleutian Islands, Japan, the Pamir-Hindu Kush (PHK), Tonga, and Bolivia. For each sequence we determine the modified Omori law (MOL) p value and goodness of fit. For all sequences, we are able to find a time interval where the sequence conforms to MOL decay with either c ≡ 0 or c variable. The two sequences with deep-focus mainshocks have slightly larger p values than the intermediate depth sequences. Despite the rarity of well defined intermediate or deep aftershock sequences, neither the observed p values nor the overall sequence decay behavior significantly differ from that observed for shallow sequences.

Enhanced image detail using continuity in the MIP Z-buffer: Applications to magnetic resonance angiography

In this paper a new algorithm is presented for the segmentation and display of blood vessels from images obtained with magnetic resonance angiography (MRA) and other three-dimensional (3D) angiographic imaging techniques. The algorithm developed is based on the observation that vessels are strongly evident in the maximum intensity projection (MIP) Z-buffer as regions of high continuity and low local roughness. Roughness is measured here by the minimum chi2 value of a low-order local least-squares fit in the principal directions through each point in the MIP Z-buffer. Although some background pixels in the Z-buffer exhibit low local roughness, the size of the connected region is nearly always much smaller than even the very smallest vessels that appear in the MIP image. It is shown that by applying connectivity to the regions of low roughness, there is nearly complete separation between vascular detail and background. When connectivity is further applied in the original 3D image, vascular bed segmentation becomes nearly complete. The algorithm consists of three basic steps: a) determination of the minimum local roughness at each point in the MIP Z-buffer; b) connection of all neighboring points of low local roughness; and c) connection of all points in the original 3D image matrix that are connected to the points determined in the MIP Z-buffer and that are above an intensity threshold. The algorithm as presented is not optimized but demonstrates a very strong potential for improved portrayal of vascular detail.

Enhanced image detail using continuity in the MIP Z-buffer: applications to magnetic resonance angiography.

In this paper a new algorithm is presented for the segmentation and display of blood vessels from images obtained with magnetic resonance angiography (MRA) and other three-dimensional (3D) angiographic imaging techniques. The algorithm developed is based on the observation that vessels are strongly evident in the maximum intensity projection (MIP) Z-buffer as regions of high continuity and low local roughness. Roughness is measured here by the minimum chi2 value of a low-order local least-squares fit in the principal directions through each point in the MIP Z-buffer. Although some background pixels in the Z-buffer exhibit low local roughness, the size of the connected region is nearly always much smaller than even the very smallest vessels that appear in the MIP image. It is shown that by applying connectivity to the regions of low roughness, there is nearly complete separation between vascular detail and background. When connectivity is further applied in the original 3D image, vascular bed segmentation becomes nearly complete. The algorithm consists of three basic steps: a) determination of the minimum local roughness at each point in the MIP Z-buffer; b) connection of all neighboring points of low local roughness; and c) connection of all points in the original 3D image matrix that are connected to the points determined in the MIP Z-buffer and that are above an intensity threshold. The algorithm as presented is not optimized but demonstrates a very strong potential for improved portrayal of vascular detail.

Chemiluminescence detection in integrated post-separation reactors for microchip-based capillary electrophoresis and affinity electrophoresis.

Chemiluminescence (CL) detection based on the horseradish peroxidase (HRP) catalyzed reaction of luminol with peroxide was investigated as a post-separation detection scheme for microchip-based capillary electrophoresis. An integrated injector, separator and post-separation reactor was fabricated on planar glass wafers. The fluorescein conjugate of HRP (HRP-F1) was used as a sample for optimization of the CL detector response. In devices etched 10 microm deep, with an aluminum mirror integrated onto the backside of the detection zone to enhance collection efficiency, the detection limit, estimated at 3 standard deviations (SD) above background noise, for 1 nL injected sample plugs was 35 nM in HRP-F1. In devices etched 40 microm deep, 8 nL plugs gave a detection limit of 7 nM. Separation and CL detection of the products of an immunological reaction of a F(ab')2 fragment of the HRP conjugate of goat anti-mouse immunoglobulin G (IgG) with mouse IgG was performed on-chip. A linear calibration curve was obtained for the decrease in peak height of the HRP conjugate (53 microg/mL) with increasing mouse IgG (0-60 microg/mL). When microperoxidase was used as an internal standard, the R2 value of a linear least-squares fit was 0.9867, and the relative errors in the slope and intercept were +/- 5.8 and +/- 1.3 %, respectively.

Prediction of composition traits of young Charolais bull carcasses using a morphometric method

The relationships among morphological traits and bovine carcass composition traits were analysed in order to select carcass measurements to derive equations for predicting muscle weight, percentage of muscle and muscle to bone ratio. The sample, constituted by 35 young Charolais bulls slaughtered at 18 months old, was homogeneous, e.g. half carcass weight = 225 ± 13.2 kg (standard deviation), carcass fat% = 6.4 ± 1.0, carcass muscle% = 74.58 ± 1.47, carcass bone% = 16.87 ± 0.83. Carcasses were weighed and a sub-group of carcass measurements was selected from the results of a principal component analysis, performed on 76 measurements taken from carcass photographs. The computation of the best combination of variables for prediction was based on the Mallows' Cp statistic and linear regression. The percentage of muscle was best predicted by only three carcass measurements with a relatively low value of fit ( R 2 = 0.70). When carcass weight was added to the same measurements to obtain the best prediction for muscle weight, the fit was high ( R 2 = 0.98). The prediction of muscle to bone ratio required nine variables and again the fit was high ( R 2 = 0.90).

Pulmonary capillary pressure measured with a pulmonary arterial double port catheter in surgical patients.

We developed a pulmonary artery (PA) double port catheter technique for reliable clinical measurements of pulmonary capillary pressure (Ppc). In seven elective surgical patients, the PA double port catheter with the second PA port 1 cm proximal to the balloon was inserted. The two PA ports, connected to identical pressure measuring systems, provided the pulmonary arterial pressures (Ppa) distal and proximal to the balloon. After general anesthesia was stabilized, the two Ppas were measured simultaneously during a PA occlusion maneuver during 10 s of apnea. The instant of occlusion was determined precisely as the time when the two Ppa traces sharply diverged. A single exponential equation was fitted to the segment of distal Ppa tracing starting 0.3 s after the instant of occlusion. Ppc was determined as the value of the exponential fit extrapolated to time 0. In six of seven patients, PA occlusion occurred consistently in the early systolic phase regardless of the timing of balloon inflation. Mean Ppa, Ppc, and pulmonary arterial wedge pressure were 16.6, 11.8, and 7.6 torr. The ratio of venous to total resistance ranged from 0.37 to 0.54 (mean:0.46). We conclude that this technique is clinically feasible and valuable in precise definition of the instant of PA occlusion. By defining PA occlusion consistently, this technique can provide reliable Ppc estimation in the clinical settings.

Characterisation of decay of frequency induced potentiation and post-extrasystolic potentiation

The aim was to elucidate the processes underlying the beat by beat decay of frequency induced and post-extrasystolic potentiation. The ventricular pacing protocol consisted of a "priming period" followed by a "decay" period of pacing at 1 s intervals, characterised by a decaying potentiation of left ventricular (LV) dP/dtmax; these were identified as test beats 1,2,3,4,5. The magnitude of potentiation of test beat 1 (P1) was increased both by increased priming frequency (frequency potentiation) and by alternately shorter priming intervals (paired pulse stimulation) at a given average frequency (post-extrasystolic potentiation). The exponential decay constant (P2) and the asymptotic value (P3) were determined and compared with the measured values and with the slope of the linear relationship between the contractility of one beat and that of the preceding beat. The lowest values after decay were related to the magnitude of preceding potentiation. Six anaesthetised dogs with induced heart block and beta adrenergic blockade were used. Beat to beat interval was controlled by ventricular pacing from a programmable stimulator. Contractility of each beat was assessed from maximum rate of rise of LV pressure (LVdP/dtmax) obtained from an intraventricular micromanometer. The asymptotic value of the exponential fit to the decay of potentiation (P3) was found to be below the measured nadir value, which was followed by an increase in LVdP/dtmax to the final steady state value P4. The decay constant (P2) was found to be equivalent to the natural logarithm of the slope of the linear relationship between the contractility of one beat and that of the preceding beat; it was unaffected by priming frequency or interval at a given average priming frequency. The asymptote P3 was inversely related to P1. P1 was interpreted as the expression of accumulation of activator in an internal release store; P3 was interpreted as a manifestation of negative feedback control of activator entry by the released activator itself, and the slow recovery to P4 as due to the slow lengthening of action potential duration and/or recovery from accumulation of an intracellular metabolite or ion.

Robust Locally Weighted Regression and Smoothing Scatterplots

Abstract The visual information on a scatterplot can be greatly enhanced, with little additional cost, by computing and plotting smoothed points. Robust locally weighted regression is a method for smoothing a scatterplot, (x i , y i ), i = 1, …, n, in which the fitted value at z k is the value of a polynomial fit to the data using weighted least squares, where the weight for (x i , y i ) is large if x i is close to x k and small if it is not. A robust fitting procedure is used that guards against deviant points distorting the smoothed points. Visual, computational, and statistical issues of robust locally weighted regression are discussed. Several examples, including data on lead intoxication, are used to illustrate the methodology.