Accounting for the competing risk of death to predict kidney failure in adults with stage 4 chronic kidney disease

IMPORTANCE Kidney failure risk prediction has implications for disease management, including advance care planning in adults with severe (ie, estimated glomerular filtration rate [eGFR] category 4, [G4]) chronic kidney disease (G4-CKD). Existing prediction tools do not account for the competing risk of death.OBJECTIVE To compare predictions of kidney failure (defined as estimated glomerular filtration rate [eGFR] <10 mL/min/1.73 m(2) or initiation of kidney replacement therapy) from models that do and do not account for the competing risk of death in adults with G4-CKD.DESIGN, SETTING, AND PARTICIPANTS This prognostic study linked population-based laboratory and administrative data (2002-2017) from 2 Canadian provinces (Alberta and Manitoba) to compare 3 kidney risk models: the standard Cox regression, cause-specific Cox regression, and Fine-Gray subdistribution hazard model. Participants were adults with incident G4-CKD (eGFR 15-29 mL/min/1.73 m(2)). Data analysis occurred between July and December 2020.MAIN OUTCOMES AND MEASURES The performance of kidney risk models at prespecified times and across categories of baseline characteristics, using calibration, reclassification, and discrimination (for competing risks). Predictive characteristics were age, sex, albuminuria, eGFR, diabetes, and cardiovascular disease.RESULTS The development and validation cohorts included 14 619 (7070 [48.4%] men; mean [SD] age, 74.1 [12.8] years) and 2295 (1152 [50.2] men; mean [SD] age, 71.9 [14.0] years) adults, respectively. The 3 models had comparable calibration up to 2 years from entry. Beyond 2 years, the standard Cox regression overestimated the risk of kidney failure. At 4 years, for example, risks predicted from standard Cox were 40% for people whose observed risks were less than 30%. At 2 years (risk cutoffs 10%-20%) and 5 years (risk cutoffs 15%-30%), 788 (5.4%) and 2162 (14.8%) people in the development cohort were correctly reclassified into lower- or higher-risk categories by the Fine-Gray model and incorrectly reclassified by standard Cox regression (the opposite was observed in 272 patients [1.9%] and 0 patients, respectively). In the validation cohort, 115 (5.0%) individuals and 389 (16.9%) individuals at 2 and 5 years, respectively, were correctly reclassified into lower- or higher-risk categories by the Fine-Gray model and incorrectly reclassified by the standard Cox regression; the opposite was observed in 98 (4.3%) individuals and 0 individuals, respectively. Differences in discrimination emerged at 4 to 5 years in the development cohort and at 1 to 2 years in the validation cohort (0.85 vs 0.86 and 0.78 vs 0.8, respectively). Performance differences were minimal during the entire follow-up in people at lower risk of death (ie, aged <= 65 years or without cardiovascular disease or diabetes) and greater in those with a higher risk of death. At 5 years, for example, in people aged 65 years or older, predicted risks from standard Cox were 50% where observed risks were less than 30%. Similar miscalibration was observed at 5 years in people with albuminuria greater than 30 mg/mmol, diabetes, or cardiovascular disease.CONCLUSIONS AND RELEVANCE In this study, predictions about the risk of kidney failure were minimally affected by consideration of competing risks during the first 2 years after developing G4-CKD. However, traditional methods increasingly overestimated the risk of kidney failure with longer follow-up time, especially among older patients and those with more comorbidity.Development and application of statistical models for medical scientific researc

Simple nanometric magnon multiplexer

We study, in the frame of the discrete dipole approximation, the magnons propagation through a simple multiplexing device made of chains of magnetic nanoparticles along which a small chains (called a resonators) is attached. We show that this simple structure can transfer with selectivity one magnon frequency from one chain to the other, leaving neighbour magnonic frequencies unaffected. With an appropriate choice of the geometrical (or magnetic) parameters of the structure, it is possible to control the desired magnon ejection. A general analytical expression for the transmission coefficient is given for various structures of this kind within the framework of the Green's function method. The amplitude, the phase, and the phase time of the transmission are discussed as a function of frequency. These results may opens new perspectives for constructing, more efficient and more compact, magnonic devices such as narrow-frequency microwave multiplexers

Existence and collapse of Fano resonances as a function of pinning field in simple mono-mode magnetic circuits

We consider, in the frame of long-wavelength Heisenberg model, the effect of a pinning field on the spin wave band gaps and transmission spectra of a simple magnonic device. This simple device is composed of an infinite one dimensional (1D) monomode waveguide (the backbone) along which N (N') side resonators are grafted at two sites. Using a Green's function method, we obtained closed-form expressions for the transmission coefficients for various systems of this kind. The amplitude, the phase, and the phase time of the transmission are discussed as a function of frequency and the strength of the pinning field parameter. In the presence of the pinning field at the ends of the side branches, the transmission probability may exhibit resonances of the Fano type. It is shown that the transition from strong to weak pinning leads to Fano line shapes with gradually smaller asymmetry. This also results in a modification of the position and the width of the resonance but the transmission amplitude remain unaffected. Furthermore, it is shown that the presence of the pinning field causes systematic collapse of certain Fano resonances. These results may provide useful means for the design of narrow-frequency optical or microwave filters

A simple phonon multiplexer

Simple multiplexing phonon structures are presented. Such structures can be deposited on a surface with current ultra-high vacuum technologies. In the atomic domain they are supposed to be made out of two parallel mono-atomic chains of atoms and of a simple coupling device made out of two other atoms interacting together and with the two chains. We show analytically that these simple structures can transfer with selectivity and directivity one phonon from one chain to the other, leaving neighbor phonons unaffected. We give closed-form relations enabling to obtain the values of the relevant physical parameters for this multiplexing phenomenon to happen at a chosen wavelength. Finally, we illustrate this general theory by an application

Effect of pinning fields on the spin wave band gaps in comblike structures

We consider, in the frame of the long-wavelength Heisenberg model, the effect of a pinning field on the spin wave band gaps and transmission spectra of one-dimensional comb-like structures. Using a Green's function method, we obtained closed-form expressions for the band structure and the transmission coefficients for an arbitrary value of the number N of sites (N'of resonators) in the comb-like structure. We report the opening-up of stop bands inside the pass-bands due to the effect of the pinning field at the ends of the resonators of the comb. These structures, composed of one-dimensional ferromagnetic materials, may exhibit large gaps where the propagation of spin waves is forbidden. The width and frequency position of these gaps depends on the strength of the pinning field

Transmission gaps and sharp resonant states in the electronic transport through a simple mesoscopic device

A simple electronic circuit consisting of a single symmetric or asymmetric loop with dangling resonators is designed to obtain possibly large stop bands (where the propagation of electrons is forbidden). Contrary to all known systems of this kind, a spectral transmission gap of nonzero width occurs here even with a single loop. This is obtained by combining appropriately the zeros of transmission of the loop and of the dangling resonators. Sharp resonant electronic states inside the gaps can be achieved without introducing any defects in the structure. This results from an internal resonance of the structure when such a resonance is situated in the vicinity of a zero of transmission or squeezed between two zeros of transmission, the so-called Fano resonances. A general expression for the transmission coefficient is given for various systems of this kind within the framework of the interface response theory. The amplitude and the phase of the transmission are discussed as a function of the wave vector or energy and it is shown that the width of the stop bands is very sensitive to the number of grafted resonators, while the magnitude of the resonant states in the transmission coefficient is very sensitive to the lengths of the different arms constituting the loop and the dangling resonators. These structures may have potential applications in microelectronic devices

Spin-wave transport in serial loop structures

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Y-shaped magnonic demultiplexer using induced transparency resonances

We give an analytical demonstration of the possibility to realize a simple magnonic demultiplexer based on induced transparency resonances. The demultiplexer consists on an Y-shaped waveguide with an input line and two output lines. Each line contains two grafted stubs at a given position far from the input line. We derive in closed form the analytical expressions for selective transfer of a single propagating mode through one line keeping the other line unaffected. This is performed through magnonic induced transparency resonances (MIT) characterized by a resonance squeezed between two transmission zeros. The existence of a complete transmission beside a zero transmission, enables to select a given frequency on one output line, by canceling the transmission on the second line as well as the reflection in the input line. Also, we show that despite the existence of a bifurcation of the input line on two output lines, the transmission through each line can be written following a Fano line shape. In addition, in order to understand better the scattering properties of the filtered resonances, we give the analytical expressions of Fano parameter q and quality factor Q of the MIT resonance in each line. The spatial distribution of the spin waves associated to different MIT resonances is performed through an analysis of the magnetization of these modes. Also, the effect of attenuation on the transmission spectra and the quality of demultiplexing is also discussed. The theoretical results are performed using the Green’s function approach which enables to deduce in closed form, the transmission and reflection coefficients as well as the densities of states