Presence Of Inflection Points Research Articles

The Epidemiology of Inflammatory Bowel Diseases During the COVID-19 Pandemic: Comparison of Two Nationwide Cohorts.

We aimed to explore the epidemiology of inflammatory bowel diseases [IBD] in association with the COVID-19 pandemic in two countries with different lockdown policies. We utilized nationwide IBD cohorts in Israel and Sweden to explore the incidence of IBD during the pandemic compared to 3 years prior [2017-2019]. We examined temporal trends through the presence of inflection points by Joinpoint regression analysis and reported average monthly percentage changes [AMPC]. A total of 155 837 patients with IBD were included [Israel, 58 640; Sweden, 97 197]. The annual incidence of IBD was stable until 2019 in both countries but then decreased in Israel (AAPC -16.6% [95% confidence interval, CI, -19.9% to -10.0%]) and remained stable in Sweden (AAPC -3.5% [95% CI -11.6% to 3.7%]). When exploring the monthly incidence during the pandemic, in Israel the rate remained stable until November 2020 (AMPC 2.3% [95% CI -13.4% to 29.9%]) and then decreased sharply (AMPC -6.4% [95% CI -20.8% to 17.0%] until February 2021 and to -20.1% [95% CI -38.9% to -4.7%] from February 2021), while in Sweden, which had a less stringent lockdown policy, it decreased slightly until July 2020 (AMPC -3.3% [95% CI -21.6% to 20.3%]), but increased thereafter (AMPC 13.6% [95% CI -12.6% to 27.0%]). The change of incidence rate in Sweden occurred mainly in elderly-onset patients, the only population with significant restrictions during the pandemic. The incidence of IBD decreased during the pandemic in association with lockdowns, more so in Israel, which had more stringent policies. Future studies are needed to determine the long-term effect of the pandemic on IBD.

P1097 The effect of lockdowns during the COVID-19 pandemic on the epidemiology of inflammatory bowel diseases: a comparison of two nationwide cohorts

Abstract Background Mechanistic evidence suggest a link between COVID-19 infections and the development of immune mediated diseases. Additionally, the lockdowns during the pandemic limited the accessibility to medical care, possibly leading to reduced number of diagnosed patients with inflammatory bowel disease (IBD). We aimed to explore these contending trends on the epidemiology of IBD during the COVID-19 pandemic in two countries with different lockdown policies. Methods We utilized nationwide IBD cohorts in Israel and Sweden to explore the incidence of IBD during the pandemic (2020-2021) compared to three years prior (2017- 2019). We examined temporal trends through the presence of inflection points by Joinpoint regression analysis and reported average monthly percentage changes (AMPC). Results A total of 155,837 patients with IBD were included (Israel, 58,640; Sweden, 97,197). The incidence of IBD was stable during the three years prior to the beginning of the COVID-19 pandemic in February 2020 (AMPC: Israel 0.0% [95%CI -0.5% to 0.4%]; Sweden 0.2% [95%CI -0.3% to 0.7]). Thereafter, the incidence rate in Israel remained stable until November 2020 (AMPC 2.3% [95% CI -13.4% to 29.9%]) and then decreased sharply (AMPC -6.4% [95%CI-20.8% to 17.0%]) until February 2021 and -20.1% [95%CI -38.9% to -4.7%]) from February 2021), while in Sweden, which had a less stringent lockdown policy, the incidence rate decreased slightly until July 2020 (AMPC -3.3% [95%CI -21.6% to 20.3%]), but increased thereafter (AMPC 13.6% [95%CI -12.6% to 27.0%]; Figure). In Israel, the reduced incidence rate during the pandemic (February 2020 to July 2021) was notable mainly in the adult-onset disease, while in Sweden, although the overall incidence rate increased steadily across all age groups, the largest change was apparent among the elderly. Conclusion In this study of two nationwide cohorts we found that the initial decrease in incidence of IBD was most apparent in Israel with a more stringent lookdown policy and among elderly in Sweden, the only population there with significant social restrictions during the pandemic. Taken together, it is likely that the reduced incidence stemmed from the limited access to the healthcare system. Future studies are needed to determine the long-term effect of the pandemic on IBD incidence.

Determination of the Curie temperature of structural alloys by analyzing the electrical characteristics of wires

The Curie temperature for many structural multicomponent alloys can only be estimated approximately, for example, from state diagrams. The necessity of an operational assessment of this parameter arises in the design of technologies for processing and controlling structural materials, in mathematical modeling of physical processes. The paper describes an experimental method for determining the temperature of magnetic transformation by measuring the temperature dependences of inductance and electrical resistance of wire samples. Verification of the procedure was carried out by determining the Curie temperature of nickel and comparing it with data obtained by other methods. We established the dependence of the Curie temperature of nickel on the carbon content and determined the Curie temperatures for alloys of Fe-Cr and Fe-Ni systems. Using numerical modeling and experimental data, temperature dependences of the relative magnetic permeability of materials were obtained. The results show the presence of the Hopkinson effect in the materials under study and the presence of inflection points on the electrical resistance curves.

Power management of variable capacitors in electrical grid systems according to the criterion of mini-mum energy loss

The aim is to manage the transmitted reactive power in electrical grids using variable capacitor batteries according to the criterion of minimum energy loss under different annual reactive load schedules and different numbers of variable capacitor sections. The main theoretical relations were obtained by the methods of mathematical modelling and integral calculus using the theory of optimal control. The influence of the power and number of sections in a capacitor battery on energy losses in the grid was estimated using computational experiments. Dependencies for energy losses in a capacitor battery, as well as for reducing energy losses in the grid, were obtained. These expressions are valid for linearized load schedules. It is shown that the dependences of energy losses in a capacitor battery and the reduction of losses in the grid on the section power have inflection points and pass through a maximum. The presence of inflection points is associated with a change in the number of capacitor sections operating throughout the year. The presence of a maximum is explained by the fact that, with an increase in the power of the capacitor battery, its operating time decreases under the complete number of variable sections. It is established that the batteries of static capacitors with two variable sections can reduce energy losses when transmitting reactive power by over 90%. For three- and four-section static capacitors, the loss reduction is close to 100%. The reduction in energy losses increases when approaching maximal levels of annual reactive load. Energy losses in electrical grid systems can be reduced by capacitor batteries with no more than three or four variable sections. In most cases, this can be achieved by two-section capacitor batteries.

Regularization on a rapidly varying manifold

The presence of inflection points on data manifold or rapid variation makes it difficult for the second order derivative based graph Laplacian and Hessian regularization techniques to accurately approximate the marginal distribution parameters. Moreover, in general, function over-fitting on seen unlabeled instances due to lack of extrapolation power which makes graph Laplacian regularization based solution biased towards constant. Hessian solves this problem by opting a generic function based on the function’s divergence in more than one direction. However, due to the presence of inflection points in the dense region, the function remains unpenalized by Hessian manifold regularization. We propose a Jerk based manifold regularization (JR) for dense, oscillating and manifolds with inflection points. JR approximates the rate of change of curvature from the underlying manifold which appropriately identifies the unpenalized geodesic deviating functions and accurately penalizes them. It also helps in identifying the optimal function in the presence of inflection points. Extensive experiments on synthetic and real-world datasets show that the proposed JR technique approximates accurate and generic input space geometrical constraints to outperform existing state-of-the-art manifold regularization techniques by a significant margin.

Flow instability in weakly eccentric annuli

A temporal linear stability analysis of laminar flow in weakly eccentric annular channels has been performed. It has been shown that, even for eccentricities ε and Reynolds numbers that were much smaller than those considered in previous studies, flow instability occurred in the form of travelling waves having characteristics that are very different from those of Tollmien-Schlichting waves and which were triggered at mid-gap by an inviscid mechanism that is associated with the presence of inflection points in azimuthal profiles of the base velocity. The critical stability conditions have been determined for 0 ≤ ε ≤ 0.1 and for diameter ratios 0 < γ < 1. The critical Reynolds number Rec decreased with increasing γ for 0 < γ ≲ 0.13, reached a minimum at γ ≈ 0.13, and increased with further increase in γ. The lowest observed Rec was 529 and occurred for ε = 0.1 and γ ≈ 0.13. As ε → 0, Rec ∝ ε−2. The critical wave number and the critical frequency of the disturbances decreased with increasing γ and approached zero as γ → 1, whilst their ratio was nearly constant in the range of parameters considered in this study. The most unstable regions were found to be at roughly mid-gap on the two flanks of the annulus, and the phase speed of the disturbances was close to the base flow velocity at these regions.

Thermohaline‐Shear Instability

AbstractThis study presents the linear theory of thermohaline‐shear instability, which is realized in oceanic flows that are dynamically and diffusively stable. The framework is based on the unbounded Couette model, which makes it possible to decouple the destabilizing effects of spatially uniform shear from instabilities caused by the presence of inflection points in velocity profiles. The basic state is assumed to be time dependent, which reflects the role of internal waves in controlling fine‐scale shear. Linear stability analysis suggests that conditions for thermohaline‐shear instability are met in most ocean regions where temperature and salinity concurrently increase downward. We conclude that thermohaline‐shear instability represents a plausible mechanism for the initiation of active diffusive convection, which, in turn, is essential for the formation of thermohaline staircases and maintenance of double‐diffusive interleaving.

Space–time dynamics of optimal wavepackets for streaks in a channel entrance flow

The laminar–turbulent transition of a plane channel entrance flow is revisited using global linear optimization analyses and direct numerical simulations. The investigated case corresponds to uniform upstream velocity conditions and a moderate value of Reynolds number so that the two-dimensional developing flow is linearly stable under the parallel flow assumption. However, the boundary layers in the entry zone are capable of supporting the development of streaks, which may experience secondary instability and evolve to turbulence. In this study, global optimal linear perturbations are computed and studied in the nonlinear regime for different values of streak amplitude and optimization time. These optimal perturbations take the form of wavepackets having either varicose or sinuous symmetry. It is shown that, for short optimization times, varicose wavepackets grow through a combination of Orr and lift-up effects, whereas for longer target times, both sinuous and varicose wavepackets exhibit an instability mechanism driven by the presence of inflection points in the streaky flow. In addition, while the optimal varicose modes obtained for short optimization times are localized near the inlet, where the base flow is strongly three-dimensional, when the target time is increased, the sinuous and varicose optimal modes are displaced farther downstream, in the nearly parallel streaky flow. Finally, the optimal wavepackets are found to lead to turbulence for sufficiently high initial amplitudes. It is noticed that the resulting turbulent flows have the same wall-shear stress, whether the wavepackets have been obtained for short or for long time optimization.

Calculations of magnetoactive elastomer reactions in a uniform external magnetic field

The model of a magnetoactive elastomer (MAE) based on a system of single-domain fine particles distributed in an elastically deformable matrix is considered. The dependence of a deformation of samples with different concentrations of an ultra-dispersed magnetic material with a given value of a uniformly applied external magnetic field has been calculated and compared with experimental data. It is shown that the presence of inflection points is connected to the intrinsic characteristics of the magnetic filler. Changing the strength of the external magnetic field leads to an alteration of the total energy, and as a consequence promotes the restructuring of the particle distribution, which results in a non-uniform internal magnetic field. The theoretical analysis is found to agree with the experimental data.

Rayleigh Instability of Plane-parallel Liquid Flows

Studying in this paper the stability of plane-parallel flows of an ordinary liquid can be naturally translated into the language of the theory of hydrodynamic resonances. Thus, resonant absorption of oscillations induces stability of the flows of an ideal liquid having a velocity profile without inflection points (Rayleigh theorem), while resonant emission leads to Rayleigh instability in the presence of an inflection point. The flow velocity profile has an inflection point. Thus, the presence of inflection points is a necessary condition for instability. If, however, the velocity profile has inflection points, the flow is stable (Rayleigh's theorem). Note that the sign of the jump depends on whether the neutral oscillations are regarded as the limiting cases of growing or damped oscillations.

Electronic susceptibilities in systems with anisotropic Fermi surfaces

The low-temperature dependence of the spin and charge susceptibilities of an anisotropic electron system in two dimensions is analyzed. It is shown that the presence of inflection points at the Fermi surface leads, generically, to a $T\mathrm{ln}T$ dependence, and a more singular behavior, $\ensuremath{\chi}\ensuremath{\sim}{T}^{3/4}\mathrm{ln}T,$ is also possible. Applications to quasi-two-dimensional materials are discussed.

Stability Analysis of Velocity Profiles in Water-Hammer Flows

This paper performs linear stability analysis of base flow velocity profiles for laminar and turbulent water-hammer flows. These base flow velocity profiles are determined analytically, where the transient is generated by an instantaneous reduction in flow rate at the downstream end of a simple pipe system. The presence of inflection points in the base flow velocity profile and the large velocity gradient near the pipe wall are the sources of flow instability. The main parameters that govern the stability behavior of transient flows are the Reynolds number and dimensionless timescale. The stability of the base flow velocity profiles with respect to axisymmetric and asymmetric modes is studied and its results are plotted in the Reynolds number/time-scale parameter space. It is found that the asymmetric mode with azimuthal wave number 1 is the least stable. In addition, the results indicate that the decrease of the velocity gradient at the inflection point with time is a stabilizing mechanism whereas the migration of the inflection point from the pipe wall with time is a destabilizing mechanism. Moreover, it is shown that a higher reduction in flow rate, which results in a larger velocity gradient at the inflection point, promotes flow instability. Furthermore, it is found that the stability results of the laminar and the turbulent velocity profiles are consistent with published experimental data and successfully explain controversial conclusions in the literature. The consistency between stability analysis and experiments provide further confirmation that (1) water-hammer flows can become unstable; (2) the instability is asymmetric; (3) instabilities develop in a short (water-hammer) timescale; and (4) the Reynolds number and the wave timescale are important in the characterization of the stability of water-hammer flows. Physically, flow instabilities change the structure and strength of the turbulence in a pipe, result in strong flow asymmetry, and induce significant fluctuations in wall shear stress. These effects of flow instability are not represented in existing water-hammer models.

An exactly solvable Ogston model of gel electrophoresis. V. Attractive gel-analyte interactions and their effects on the Ferguson plot.

We examine the effect of attractive analyte-gel interactions within the framework of our recently developed lattice model of gel electrophoresis. We show that it is possible to take into account such interactions and still calculate exact mobilities for various analytes and gel structures. Our study then focuses on two main issues: (i) the effect of these interactions on the separation efficiency of the Ogston regime; and (ii) the presence of inflection points (changes of curvature) in Ferguson plots. We establish some general principles, and we describe the results for selected two- and three-dimensional model systems. Numerous practical problems, such as chiral separations and affinity electrophoresis, can be treated using this approach.

Zn diffusion behavior in InGaAsP/InP capped mesa buried heterostructures

A systematic study of the effects of Zn doping and diffusion in InGaAsP/InP capped mesa buried heterostructure lasers grown by metalorganic chemical vapor deposition was carried out. It consisted of varying the Zn doping of the p-InP cladding layer in the base epitaxial structure over the range (0.7–3.1)×1018 cm−3 and keeping the growth conditions in two subsequent regrowth steps the same. Secondary ion mass spectrometry was employed for a quantitative determination of the Zn depth profiles following regrowth using test sites on the 50 mm round wafers that contained the appropriate epitaxial layers. Clear evidence of Zn diffusion such as the penetration of Zn into the active layer and the presence of inflection points (accumulation and depletion of Zn near the p-n heterojunction) was illustrated in the depth profiles. It was observed that the diffusion of Zn during the third growth dominated the Zn profile in the base growth part of the p-InP layer and the final amount of Zn in this region was independent of the initial doping level. Above a Zn threshold level of ≊2.2×1018 cm−3, Zn diffusion increased significantly resulting in 5×1018/cm−3 or greater Zn in the active layer. The threshold for the onset of diffusion was found to be in accordance with the substitutional-interstitial diffusion of Zn.

Hormonal control of sex differences in the electric organ discharge (EOD) of mormyrid fishes

Field studies have demonstrated that several species of mormyrid fish from Gabon, West Africa have a sex difference in the pulse-like waveform of their Electric Organ Discharge (EOD). Administration of androgen hormones (testosterone or dihydrotestosterone) to a female or juvenile can induce the EOD typical of a sexually mature male. Data for two such species —Brienomyrus brachyistius (triphasic) andStomatorhinus corneti — are presented, showing that transformation of a female's or juvenile's EOD to a male-like EOD involves a 2–3 fold increase in EOD duration and a downward shift in the peak frequency of the EOD's power spectrum (as determined by Fourier analysis). ForBrienomyrus brachyistius (triphasic), estradiol can also induce changes in the EOD waveform, although not as dramatic as that for androgens. Changes in EOD duration and power spectra are often accompanied by an alteration of the wave-shape or ‘morphology’ of the EOD pulse, i.e., the relative amplitude of its peaks and the presence of inflection points in its negative and positive phases.

Population Breaks in Grain-Size Distributions of Sand--A Theoretical Model

ABSTRACT The model attributing the presence of inflection points (breaks) separating straight-line segments of grain-size distributions plotted on log-probability paper to the presence of three transport populations preserved in deposits permits a correlation of environmental and genetic criteria with grain-size distributions. Analysis of a physical model of sedimentation suggests applicability of the -theorem of dimensional analysis to 10 selected physical parameters functionally related to movements of break positions which control distribution curve shapes. Application of the seven terms in a described set of dimensionless numbers generated by the model to 20 selected grain-size distribution curves illustrates systematic variations. The study leads to the conjecture that grain-size distribution can be related to specific physical aspects of the depositional process by the use of seven general terms which can be used as a basis for rigorous testing of the depositional model in the laboratory.

Geometrical characteristics of noses and tails for parallel middle bodies

Abstract : Two-parameter geometric systems are developed for noses and tails attached to parallel middle bodies in terms of independent polynomials. A new parameter is introduced--the rate of change of curvature with arc length at the juncture with the parallel middle body. Quadratic polynomials are considered for bodies of revolution and square root polynomials for symmetric two- dimensional bodies. Permissible ranges of the two adjustable parameters are obtained for selected geometrical constraints such as the presence of inflection points.