Two-slope Model Research Articles

Modelling and Accelerated Testing of Catholyte Stability in Vanadium Flow Batteries

Using our standard methodology, we examined the thermal stability of vanadium flow battery positive electrolytes over a range of temperature from 30 to 70 °C with stable lifetimes from 11 min to 87 days. At higher temperatures (45 °C–70 °C) measurements showed excellent reproducibility but at lower temperatures (30 °C–45 °C) showed some scatter. Measurements at higher temperatures are in good agreement with our (single-slope) model which is based on earlier data but there is some divergence from the model at lower temperatures. Arrhenius plots of the data show two linear regimes: one in the range 45 °C–70 °C and another in the range 30 °C–45 °C, the latter having a higher Arrhenius slope. Based on linear least-squares best fits in these two regimes, we have formulated an improved stability model (two-slope model). We use our models to derive expressions for accelerated testing of thermal stability using increased temperature, increased vanadium concentration and decreased sulfate concentration and estimate values for the acceleration factors over a range of test and use temperatures and concentrations. We analyse the effect of changing concentration to counteract the decrease in electrolyte stability at higher temperatures and derive expressions to calculate the necessary concentrations.

Accelerated Testing of Vanadium Catholyte Stability

Using our standard methodology, we have examined the stability of electrolytes with compositions close to those used in actual flow batteries over a range of temperature from 70 to 30°C. Measurements at higher temperatures (45–70°C) showed excellent reproducibility but measurements at lower temperatures (30–45°C) showed some scatter. Furthermore, the measurements at higher temperatures are in good agreement with our (single-slope) model which is based on earlier data but there is some divergence from the model at lower temperatures. Arrhenius plots of the data show two linear regimes: one in the range 45–70°C and another in the range 30–45°C, the latter having a higher Arrhenius slope. Based on linear least-squares best fits in these two regimes, we have formulated an improved stability model (two-slope model). For each of the two models, we derive expressions for acceleration factors for temperature testing of catholyte stability and estimate values over a range of test and use temperatures. Acceleration factors based on the two-slope model are higher than those for the single slope model by a factor of 3–6 depending on the temperatures. Thus, predictions based on the single-slope model are more conservative.

Drivers of Frailty from Adulthood into Old Age: Results from a 27-Year Longitudinal Population-Based Study in Sweden

BackgroundFrailty is a strong predictor of adverse outcomes. However, longitudinal drivers of frailty are not well understood. This study aimed at investigating the longitudinal trajectories of a frailty index (FI) from adulthood to late life and identifying the factors associated with the level and rate of change in FI.MethodsAn age-based latent growth curve analysis was performed in the Swedish Adoption/Twin Study of Aging (N = 1,842; aged 29–102 years) using data from up to 15 measurement waves across 27 years. A 42-item FI was used to measure frailty at each wave.ResultsA bilinear, two-slope model with a turning point at age 65 best described the age-related change in FI, showing that the increase in frailty was more than twice as fast after age 65. Underweight, obesity, female sex, overweight, being separated from one’s co-twin during childhood, smoking, poor social support, and low physical activity were associated with a higher FI at age 65, with underweight having the largest effect size. When tested as time-varying covariates, underweight and higher social support were associated with a steeper increase in FI before age 65, whereas overweight and obesity were associated with less steep increase in FI after age 65.ConclusionsFactors associated with the level and rate of change in frailty are largely actionable and could provide targets for intervention. As deviations from normal weight showed the strongest associations with frailty, future public health programs could benefit from monitoring of individuals with abnormal BMI, especially those who are underweight.

Surf Shoaling and Breaking on Two-Slope Flume Experiments

A flume experiment is carried out to explore regular waves shoaling and breaking in surf zone. The topography is two-slope model, which is composed of a steep slope 1:5 and a gentle slope 1:40. The incidence waves have heights of 0.05, 0.06, 0.07, 0.08, 0.09 and 0.10 m, and periods of 1.0 sec. In order to describe the wave propagation in surf zone, wave height is collected by wave gauges and wave breaking is recorded by high-speed camera. The results show that, when incidence height is increased, the breaking height increases, while the location of breaking point moves forward. When the incidence height is larger enough, the trend slow down. Besides, secondary breakup is observed in case 0.08, 0.09 and 0.10m. The transient period from primary breakup to secondary breakup is a very important phase. Computing and forecasting methods of surf with complicated topography need further study.

Healthcare Costs Associated with Change in Body Mass Index in Patients with Type 2 Diabetes Mellitus in Spain

Background: Weight management is considered a key therapeutic strategy in type 2 diabetes mellitus. However, little is known about the impact of weight loss or body mass index (BMI) reduction on type 2 diabetes-related healthcare costs. Objective: The aim of this study was to estimate the economic impact of change in BMI among patients with type 2 diabetes mellitus from the Spanish healthcare system perspective. Methods: The ECOBIM study is an observational, non-interventional study in which data on BMI change and costs incurred by patients with type 2 diabetes were collected cross-sectionally and retrospectively for a 12-month period. Generalized linear mixed models were applied to estimate the effects of (i) BMI change in general (one-slope model); (ii) BMI gain and no BMI gain (two-slope model); and (iii) BMI gain and no BMI gain among obese and non-obese patients (four-slope model). Results: We studied 738 patients with a mean (SD) age of 66 (11) years and BMI of 30.6 (5.2) kg/m2. During the 12-month study period, 41.2% of patients gained BMI (BMI gainers) and 58.8% experienced either loss (52.2%) or no change (6.6%) in BMI (non-BMI gainers). One-unit gain (or loss) in BMI was significantly (p<0.001) associated with a 2.4% cost increase (or decrease) [one-slope model]. Every unit gain in BMI was associated with a 20.0% increase in costs among BMI gainers while losing one unit was associated with an 8.0% decrease in costs among non-BMI gainers (two-slope model, p<0.01). The economic benefit associated with reducing one BMI unit was 9.4% cost decrease in obese and 2.7% in non-obese patients (4-slope model). Conclusion: An increase in BMI among patients with type 2 diabetes was associated with increased 1-year direct healthcare costs. A reduction in BMI was associated with appreciable short-term economic benefits, especially in obese patients.

Healthcare Costs Associated with Change in Body Mass Index in Patients with Type 2 Diabetes Mellitus in Spain

Background: Weight management is considered a key therapeutic strategy in type 2 diabetes mellitus. However, little is known about the impact of weight loss or body mass index (BMI) reduction on type 2 diabetes-related healthcare costs.Objective: The aim of this study was to estimate the economic impact of change in BMI among patients with type 2 diabetes mellitus from the Spanish healthcare system perspective.Methods: The ECOBIM study is an observational, non-interventional study in which data on BMI change and costs incurred by patients with type 2 diabetes were collected cross-sectionally and retrospectively for a 12-month period. Generalized linear mixed models were applied to estimate the effects of (i) BMI change in general (one-slope model); (ii) BMI gain and no BMI gain (two-slope model); and (iii) BMI gain and no BMI gain among obese and non-obese patients (four-slope model).Results: We studied 738 patients with a mean (SD) age of 66 (11) years and BMI of 30.6 (5.2) kg/m2. During the 12-month study period, 41.2% of patients gained BMI (BMI gainers) and 58.8% experienced either loss (52.2%) or no change (6.6%) in BMI (non-BMI gainers). One-unit gain (or loss) in BMI was significantly (p<0.001) associated with a 2.4% cost increase (or decrease) [one-slope model]. Every unit gain in BMI was associated with a 20.0% increase in costs among BMI gainers while losing one unit was associated with an 8.0% decrease in costs among non-BMI gainers (two-slope model, p<0.01). The economic benefit associated with reducing one BMI unit was 9.4% cost decrease in obese and 2.7% in non-obese patients (4-slope model).Conclusion: An increase in BMI among patients with type 2 diabetes was associated with increased 1-year direct healthcare costs. A reduction in BMI was associated with appreciable short-term economic benefits, especially in obese patients.

Near-Ground Path Loss Measurements and Modeling for Wireless Sensor Networks at 2.4 GHz

Near-ground channel characterization is an important issue in most military applications of wireless sensor networks. However, the channel at the ground level lacks characterization. In this paper, we present a path loss model for three near-ground scenarios. The path loss values for each scenario were captured through extensive measurements, and then a least-square linear regression was performed. This indicates that the log-distance-based model is still suitable for path loss modeling in near-ground scenarios, and the prediction accuracy of the two-slope model is superior to that of the one-slope model. The validity of the proposed model was further verified by comparisons between the predicted and measured far-field path losses. Finally, compared to the generic models, the proposed model is more effective for the path loss prediction in near-ground scenarios.

Distortion-product otoacoustic emission input/output characteristics in normal-hearing and hearing-impaired human ears

Distortion-product otoacoustic emission (DPOAE) input/output (I/O) functions were measured in 322 ears of 176 subjects at as many as 8 f(2) frequencies per ear for a total of 1779 I/O functions. The f(2) frequencies ranged from 0.7 to 8 kHz in half-octave steps. Behavioral thresholds (BTs) at the f(2) frequencies ranged from -5 to 60 dB hearing loss (HL). Both linear-pressure and nonlinear, two-slope functions were fitted to the data. The two-slope function describes I/O compression as output-controlled self-suppression. Most I/O functions (96%) were better fitted by the two-slope method. DPOAE thresholds based on each method were used to predict BTs. Compared to estimates based on linear-pressure functions, individual BTs predicted from DPOAE thresholds based on the two-slope model had lower residual error and accounted for more variance. Another advantage of the two-slope method is that it provides an estimate of response growth rate (RGR) that is not tied to threshold. At all frequencies, the median low-level RGR (across I/O functions of the same f(2) and BT) usually increased as BT increased, while high-level compression decreased. The observed characteristics of DPOAE I/O functions are consistent with the loss of cochlear compression that is typically associated with mild-to-moderate HL.

Cognitive Positioning Systems

Location awareness is one of the essential characteristics of cognitive radios. In this paper, an innovative cognitive positioning system (CPS) that achieves accuracy adaptation in both indoor and outdoor environments is proposed as a step towards realization of location awareness in cognitive radios. The proposed CPS is composed of two modes; bandwidth determination and enhanced dynamic spectrum management (EDSM). Bandwidth determination equations are derived through Cramer-Rao Lower Bound (CRLB) for both additive white Gaussian noise (AWGN) and multipath channels. An EDSM system providing the optimum available bandwidth to the CPS is proposed. Overlay spectrum access based EDSM (O-EDSM) and hybrid overlay and underlay spectrum access based EDSM (H-EDSM) are two schemes that are introduced. A switching mechanism that manages the transition between underlay and overlay spectrum usage modes for the H-EDSM algorithm is presented. The theoretical analysis of the mechanism is carried out using Two-slope model. Simulation results, challenges and complexity options for the implementation of the CPS are outlined. Our study reveals the existence of a trade-off between the accuracy and complexity in the cognitive positioning systems.

WCDMA uplink capacity and interference statistics of highways cigar-shaped microcells

The capacity and the interference statistics (mean value and variance) of the sectors of the cigar-shaped Wideband Code Division Multiple Access microcells are studied. The two-slope propagation model is used in the analysis. A model of five microcells is used to calculate the uplink capacity and interference statistics assuming highways cigar-shaped microcells. The capacity and the interference statistics of the microcell are studied for different sector range, propagation exponent, antenna side lobe levels and different standard deviation of the power control error. It is noticed that the quasi-maximum uplink sector capacity can be got when the sector range R is between 600 and 1,200 m and the sidelobe level of the directive antenna used in each sector is on the order of ?15 dB.

Fluctuation analysis of the far-infrared background - information from the confusion

We investigate the extent to which one can use a P(D) analysis to extract number counts of unclustered sources from maps of the far-infrared background. Such maps currently available, and those expected to emerge in the near future, are dominated by confusion noise resulting from poor resolution. We simulate background maps with an underlying two-slope model for N(S), and we find that, in an experiment of FIRBACK type, we can extract the high-flux slope with an error of a few per cent, whereas other parameters are not so well constrained. However, we find that, in a SIRTF-type experiment, all parameters of this N(S) model can be extracted with errors of only few per cent.

Input-output functions for stimulus-frequency otoacoustic emissions in normal-hearing adult ears.

Input-output (I/O) functions for stimulus-frequency (SFOAE) and distortion-product (DPOAE) otoacoustic emissions were recorded in 30 normal-hearing adult ears using a nonlinear residual method. SFOAEs were recorded at half octaves from 500-8000 Hz in an L1=L2 paradigm with L2=0 to 85 dB SPL, and in a paradigm with L1 fixed and L2 varied. DPOAEs were elicited with primary levels of Kummer et al. [J. Acoust. Soc. Am. 103, 3431-3444 (1998)] at f2 frequencies of 2000 and 4000 Hz. Interpretable SFOAE responses were obtained from 1000-6000 Hz in the equal-level paradigm. SFOAE levels were larger than DPOAEs levels, signal-to-noise ratios were smaller, and I/O functions were less compressive. A two-slope model of SFOAE I/O functions predicted the low-level round-trip attenuation, the breakpoint between linearity and compression, and compressive slope. In ear but not coupler recordings, the noise at the SFOAE frequency increased with increasing level (above 60 dB SPL), whereas noise at adjacent frequencies did not. This suggests the existence of a source of signal-dependent noise producing cochlear variability, which is predicted to influence basilar-membrane motion and neural responses. A repeatable pattern of notched SFOAE I/O functions was present in some ears, and explained using a two-source mechanism of SFOAE generation.

Classical and quantum models for phase imprinting

We investigate theoretically the generation of a persistent current in a Bose-Einstein condensate in a toroidal trap by means of phase imprinting. The phase-imprinting potential must be periodic around the torus, and will have parts that accelerate atoms in the direction opposite to the intended flow. We study the evolution of the average momentum and the momentum spread under a two-slope model potential numerically by using the Gross-Pitaevskii equation, and also in a simple classical-mechanics analogy. Because of the inevitable pollution caused by the opposite slopes of the potential, it is not possible to generate a pure persistent current. The same caveat presumably applies to vortices in higher-dimensional systems.

Association of serum albumin and atherosclerosis in chronic hemodialysis patients

Background: Because cardiovascular disease is the leading cause of death and hypoalbuminemia predicts mortality, hypoalbuminemia may be associated with atherosclerosis. Methods: In 1,411 patients enrolled in the HEMO study, associations of albumin with the presence of coronary artery disease (CAD), cerebrovascular disease (CVD), peripheral vascular disease (PVD), and any one of the three conditions at baseline were examined using multivariable logistic regression models. Results: In the two-slope model, when albumin level was 3.6 g/dL (36 g/L) or greater, with each 1-g/dL (10-g/L) increase in albumin level the odds for CAD (odds ratio [OR], 0.32; 95% confidence interval [CI], 0.17 to 0.59), PVD (OR, 0.39; 95% CI, 0.18 to 0.80), CVD (OR, 0.33; 95% CI, 0.15 to 0.73), and any one of the three conditions (OR, 0.23; 95% CI, 0.12 to 0.44) decreased. When albumin level was less than 3.6 g/dL (36 g/L), none of the conditions was statistically significantly associated with each 1-g/dL (10-g/L) increase in albumin level. When normal- and low-albumin groups were compared with each other, patients with albumin levels less than 3.6 g/dL (36 g/L) had a higher association with CAD (OR, 1.32; 95% CI, 1.03 to 1.70) and for any one of the three conditions (OR, 1.38; 95% CI, 1.07 to 1.78). Conclusion: The odds for atherosclerosis linearly decreased as albumin level increased in the normal-albumin group, and a plateau was seen in the low-albumin group; however, the low-albumin group had significantly greater CAD. The nonlinearity of association of albumin level with prevalence of atherosclerosis might be due to the cross-sectional nature of the study of higher mortality with hypoalbuminemia. © 2002 by the National Kidney Foundation, Inc.

Outer edges of face-on spiral galaxies

We present deep optical imaging of three face-on disk galaxies together with a detailed description of the reduction and calibration methods used, in order to measure the intrinsic shape of their outer stellar edges. Whereas it is now well accepted that disks of spiral galaxies are not infinite exponential beyond galactocentric distances of about 3-5 radial scalelengths, the genuine structure of the truncation region is not yet well known. Our data quantitatively establish a smooth truncation behaviour of the radial surface brightness profiles and is best described by a two-slope model, characterised by an inner and outer exponential scalelength separated at a relatively well defined break radius. This result disagrees with the frequently assumed sharply truncated nature of the radial surface brightness profiles and implies the presence of stars and even star-formation beyond the break radius. In addition, we do not find a strong influence of a nearby companion on the ratio of the break radius to the radial scalelength. Our results denote new observational constraints for the search of the physical explanation for these smooth disk truncations.

Capacity and interference statistics of highways W-CDMA cigar-shaped microcells (uplink analysis)

The capacity and the interference statistics of the sectors of the shaped W-CDMA cell are studied. A model of five cells is used to analyze the uplink. The cells are assumed to exist in rural zones. The capacity and the interference statistics of the cell are studied using a two-slope propagation model. The expected value and the variance of the interference are given for different propagation exponent.

A comparison of quadratic versus segmented regression procedures for estimating nutrient requirements

Continued improvements in dietary formulation will require increasingly detailed knowledge of nutrient requirements. The objective of this study was to evaluate bias and precision of estimates of nutrient requirements from quadratic versus segmented regression. One hundred 0-to-3-wk turkey growth experiments were simulated to provide data with known nutrient requirements. Nine diets contained levels of an arbitrary nutrient ranging from 80 to 120% of recommended. The true nutrient requirement was uniformly randomly distributed between 90 and 110% of recommended. The requirements were estimated as the intersection of the segmented regression lines from a two-slope model, and 0.90 and 0.95 of the maximum gain predicted from quadratic regression coefficients. The mean true requirement was 99.42%, and predictions were 102.14+/−0.61, 107.81+/−0.61, and 99.59+/−0.61% for 0.90 of quadratic maximum, 0.95 of quadratic maximum and segmented regression, respectively. The segmented regression resulted in the closest prediction to the true nutrient requirement in 73 of 100 replicates. The average squared deviation of the requirement from their estimates were 15.18 for 0.90 of quadratic maximum, 78.72 for 0.95 of quadratic maximum, and 2.41 for segmented regression. The quadratic regressions yielded overestimates, particularly when the experimental diets were not centered on the requirement, suggesting that a bias can be introduced by experimental design. Segmented regression procedures resulted in more precise estimates of nutrient requirements, were less likely to suffer from bias, and required less a priori knowledge of the true requirement than did quadratic regression procedures.

Antidepressant medication and suicide in Sweden

To explore a possible temporal association between changes in antidepressant sales and suicide rates in different age groups. A time series analysis using a two-slope model to compare suicide rates in Sweden before and after introduction of the selective serotonin reuptake inhibitors, SSRIs. Antidepressant sales increased between 1977-1979 and 1995-1997 in men from 4.2 defined daily doses per 1000 inhabitants and day (DDD/t.i.d) to 21.8 and in women from 8.8 to 42.4. Antidepressant sales were twice as high in the elderly as in the 25-44-year-olds and eight times that in the 15-24-year-olds. During the same time period suicide rates decreased in men from 48.2 to 33.3 per 10(5) inhabitants/year and in women from 20.3 to 13.4. There was significant change in the slope in suicide rates after the introduction of the SSRI, for both men and women, which corresponds to approximately 348 fewer suicides during 1990-1997. Half of these 'saved lives' occurred among young adults. We demonstrate a statistically significant change in slope in suicide rates in men and women that coincided with the introduction of the SSRI antidepressants in Sweden. This change preceded the exponential increase in antidepressant sales.

Volume and secretion rate of lung liquid in the final days of gestation and labour in the fetal sheep.

1. Most of the liquid that fills the lung of the fetal sheep in late gestation is cleared by the end of labour. Clearance of this liquid has a beneficial effect on postnatal gas exchange and therefore represents an important adaptation for postnatal life. Despite its importance, there is disagreement about whether clearance begins prior to labour, or occurs entirely within labour. 2. To address this issue, we made serial determinations of lung liquid volume by indicator dilution during late gestation and labour in the fetal sheep. 3. Regression analysis demonstrated that lung liquid volume exhibited a plateau level in the near-term fetus before it began to decline. Two models provided a fit to the decline in volume. In one, lung liquid clearance occurred in two linear phases, the first beginning 70 h before the study was terminated when the ewe was in advanced labour, the second occupying the last 8 h of the study period. In the initial phase, average lung liquid volume fell from 38.3 to 26.4 ml x kg(-1) before a rapid decline in the second phase reduced the volume to 13.8 ml x kg(-1). An exponential decay model was also found to fit the data; this showed a gradual decline in lung liquid volume in the 2 days preceding onset of labour, followed by a much more rapid decline within labour. 4. The rate of lung liquid secretion also declined in two linear phases, both of which commenced earlier than the changes in lung liquid volume. An exponential decay model also gave a significant fit to the data, but the fit was significantly weaker than that achieved with the two-slope model. 5. We conclude that clearance of lung liquid begins well before commencement of labour in the full term fetal sheep, and then accelerates once labour is established. In our study, lung liquid volume fell even in the absence of reabsorption of liquid across the pulmonary epithelium, indicating that outflow of liquid through the trachea must have occurred at a rate in excess of the secretion rate.

Some Insights Into Micro-EHL Pressures

An analytical model is developed in this paper which relates the major component of micro-EHL pressure responses to lubricant properties, roughness geometry, contact load, velocity, and slide-to-roll ratio. Analyses are then conducted showing the effects of system parameters on this micro-EHL pressure. For a Newtonian lubricant with an exponential pressure-viscosity law, this pressure would be large unless the contact practically operates right at pure rolling. The magnitude of the pressure rippling is largely independent of the slide-to-roll ratio, and smaller wavelength components of the surface roughness generate larger micro-EHL pressures. With less dramatic pressure-viscosity enhancement such as the two-slope model, the micro-EHL pressure is generally smaller and sensitive to the slide-to-roll ratio, larger with higher sliding in the contact. Furthermore, this pressure-viscosity model yields a micro-EHL pressure that becomes vanishingly small corresponding to sufficiently small wavelength components of the roughness. For a shear-thinning non-Newtonian lubricant, such as the Eyring model, with an exponential pressure-viscosity law, substantially less micro-EHL pressure rippling is generally developed than its Newtonian counterpart. While the pressure rippling is insensitive of the slide-to-roll ratio like its Newtonian counterpart, it vanishes corresponding to sufficiently small wavelength components of the roughness. The analyses revealed that a key factor resulting in a smaller micro-EHL pressure with the two-slope model or the Eyring model is the lower viscosity or shear-thinned effective viscosity in the loaded region of the contact. Since EHL traction is proportional to this viscosity, contacts lubricated with oils exhibiting higher traction behavior would develop larger micro-EHL pressures and thus would be more vulnerable to fatigue failure.