Double Fronts Research Articles

Implementing front-of-pack nutrition warning labels in Mexico: important lessons for low- and middle-income countries.

To analyse the implementation of front-of-pack nutrition labelling (FOPNL) in Mexico. Review of publicly accessible documents, including legislative websites, news sources, and government, intergovernmental, and advocacy reports. Usage of the policy cycle model to analyse the implementation and evaluation stages of Mexico's General Health Law, amended with FOPNL (2019-2022). In October 2019, the government published a draft modification of the Norma Oficial Mexicana (Official Mexican Standard) to regulate and enforce a new FOPNL warning label system. A 60-d public consultation period followed (October-December 2019), and the regulation was published in March 2020 and implementation began in October 2020. An analysis of nine key provisions of the Standard revealed that the food and beverage industry and its allies weakened some original provisions including health claims, warnings for added sweeteners and display areas. On the other hand, local and international public health groups maintained key regulations including the ban on cartoon character advertisements, standardised portions and nutrient criteria following international best practices. Early implementation appears to have high compliance and helped contribute to reformulating unhealthy products. Continued barriers to implementation include industry efforts to create double fronts and market their cartoon characters on social media and through digitalised marketing. Early success in implementing the new FOPNL system in Mexico was the result of an inclusive and participatory regulatory process dedicated to maintaining public health advances, local and international health advocacy support, and continued monitoring. Other countries proposing and enacting FOPNL should learn from the Mexican experience to maintain scientifically proven best practices, counter industry barriers and minimise delays in implementation.

Fast moving smoldering fronts in thin liquid fuel films dispersed on inert porous media

An experimental study of smoldering in thin layers of pyrolysis oil on an inert substrate of calcium silicate boards has been conducted. The smoldering fronts propagated with velocities up to 0.4mm/s, which is significantly faster than other types of smoldering without forced air flow. The smoldering propagation velocity increased both with thinner layer of pyrolysis oil and higher initial fuel temperature. Our experimental observations are in close correspondence with a theoretical model based on energy balance, where the availability of oxygen at the substrate surface is the main limiting mechanism. Both the front peak temperature and the front width are correlated to the initial fuel temperature. We also report observations of instability phenomena, including double fronts propagating in close succession. The temperature dynamics were observed by high resolution infrared thermography. The findings contribute to the understanding of the governing mechanisms of smoldering combustion of liquids on inert media, and in particular the fast smoldering fronts that have been observed along the surface of porous insulating materials in experiments with smoldering cotton.

Investigating the Structural Dynamics and Crack Propagation Behavior under Uniform and Non-Uniform Temperature Conditions.

The robustness and stability of the system depend on structural integrity. This stability is, however, compromised by aging, wear and tear, overloads, and environmental factors. A study of vibration and fatigue cracking for structural health monitoring is one of the core research areas in recent times. In this paper, the structural dynamics and fatigue crack propagation behavior when subjected to thermal and mechanical loads were studied. It investigates the modal parameters of uncracked and various cracked specimens under uniform and non-uniform temperature conditions. The analytical model was validated by experimental and numerical approaches. The analysis was evaluated by considering different heating rates to attain the required temperatures. The heating rates were controlled by a proportional-integral-derivative (PID) temperature controller. It showed that a slow heating rate required an ample amount of time but more accurate results than quick heating. This suggested that the heating rate can cause variation in the structural response, especially at elevated temperatures. A small variation in modal parameters was also observed when the applied uniform temperatures were changed to non-uniform temperatures. This study substantiates the fatigue crack propagation behavior of pre-seeded cracks. The results show that propagated cracking depends on applied temperatures and associated mass. The appearance of double crack fronts and multiple cracks were observed. The appearance of multiple cracks seems to be due to the selection of the pre-seeded crack shape. Hence, the real cracks and pre-seeded cracks are distinct and need careful consideration in fatigue crack propagation analysis.

Magnetic Signatures of Radiation-Driven Double Ablation Fronts.

In experiments performed with the OMEGA EP laser system, magnetic field generation in double ablation fronts was observed. Proton radiography measured the strength, spatial profile, and temporal dynamics of self-generated magnetic fields as the target material was varied between plastic, aluminum, copper, and gold. Two distinct regions of magnetic field are generated in mid-Z targets-one produced by gradients from electron thermal transport and the second from radiation-driven gradients. Extended magnetohydrodynamic simulations including radiation transport reproduced key aspects of the experiment, including field generation and double ablation front formation.

Double fronts in the Yellow Sea in summertime identified using sea surface temperature data of multi-scale ultra-high resolution analysis

Fronts are ubiquitous phenomena in oceans, and they play a significant role in marine hydrodynamics and ecology. During the stratified season of a shelf sea, the coastal front is usually considered as a single front, i.e., the tidal mixing front. However, using high resolution (~1 km) Multi-scale Ultra-high Resolution (MUR) analysis sea surface temperature (SST) data, this study observes persistent double fronts along the Yellow Sea coast in summertime. The double fronts comprise the well-known offshore tidal mixing front and a nearshore front, and the nearshore front has not been previously reported. The climatological (2002–2017) monthly mean result shows that the double fronts with two SST gradient peaks exceeding ~2 °C/100 km and opposite SST gradient directions basically remain unchanged from June to August, whereas the frontal spacing decreases in September. Analyses based on a two-layer concept model suggest that a topographic slope along with tidal mixing could induce the pattern of double fronts. The frontogenesis of nearshore thermal front could be associated with the different responses of the water column of different water depths to insolation. The offshore movement of the nearshore front in September could be related to the fast cooling of nearshore water and intensified offshore wind, and the topographic slope is important for determining the pattern of double fronts (loose or tight). This study shows a new pattern of coastal fronts in the stratified season, and indicates the significance of high resolution satellite data. The discovery of the double front pattern implies the influence of coastal fronts during the stratified season on marine ecology and environment in a shelf sea might be underestimated.

Double SST fronts observed from MODIS data in the East China Sea off the Zhejiang–Fujian coast, China

We report a double coastal front system off the Zhejiang (Zhe) and Fujian (Min) Provinces in the East China Sea in winter. In addition to the well-known Zhe–Min offshore coastal front along 50m isobath, a secondary near-shore coastal thermal front along 20m isobath is also apparent in December and January. The fronts were observed by Moderate Resolution Imaging Spectroradiometer (MODIS) at monthly mean nighttime sea surface temperature (SST) during 2000–2013 in terms of SST gradients. Our results showed temporal and spatial variations of the two fronts as follows: (1) both offshore front and near-shore front often co-exist between 26.5°N and 29.5°N in December and between 28.0°N and 29.5°N in January. However, only the offshore front is apparent in November and February. (2) The near-shore front is narrow (4–16km), while the offshore front is three to four times wider (16–48km). (3) In contrast to the well-known offshore front which exists throughout the winter with a strong intensity, the near-shore front has a shorter lifetime with a weak intensity, and has been overlooked by previous studies. Finally, we proposed that the bottom bathymetric gradients may play an important role in the frontogenesis of the double fronts.

Instabilities of coupled density fronts and their nonlinear evolution in the two-layer rotating shallow-water model: influence of the lower layer and of the topography

AbstractWe undertake a detailed analysis of linear stability of geostrophically balanced double density fronts in the framework of the two-layer rotating shallow-water model on the $f$-plane with topography, the latter being represented by an escarpment beneath the fronts. We use the pseudospectral collocation method to identify and quantify different kinds of instabilities resulting from phase locking and resonances of frontal, Rossby, Poincaré and topographic waves. A swap in the leading long-wave instability from the classical barotropic form, resulting from the resonance of two frontal waves, to a baroclinic form, resulting from the resonance of Rossby and frontal waves, takes place with decreasing depth of the lower layer. Nonlinear development and saturation of these instabilities, and of an instability of topographic origin, resulting from the resonance of frontal and topographic waves, are studied and compared with the help of a new-generation well-balanced finite-volume code for multilayer rotating shallow-water equations. The results of the saturation for different instabilities are shown to produce very different secondary coherent structures. The influence of the topography on these processes is highlighted.

Modeling hydrodynamic instabilities of double ablation fronts in inertial confinement fusion

A linear Rayleigh-Taylor instability theory of double ablation (DA) fronts is developed for direct-drive inertial confinement fusion. Two approaches are discussed: an analytical discontinuity model for the radiation dominated regime of very steep DA front structure, and a numerical self-consistent model that covers more general hydrodynamic profiles behaviours. Dispersion relation results are compared to 2D simulations.

Global Existence and Blowup for a Parabolic Equation with a Non-Local Source and Absorption

In this paper we consider a double fronts free boundary problem for a parabolic equation with a non-local source and absorption. The long time behaviors of the solutions are given and the properties of the free boundaries are discussed. Our results show that if the initial value is sufficiently large, then the solution blows up in finite time, while the global fast solution exists for sufficiently small initial data, and the intermediate case with suitably large initial data gives the existence of the global slow solution.

Self-consistent numerical dispersion relation of the ablative Rayleigh-Taylor instability of double ablation fronts in inertial confinement fusion

The linear stability analysis of accelerated double ablation fronts is carried out numerically with a self-consistent approach. Accurate hydrodynamic profiles are taken into account in the theoretical model by means of a fitting parameters method using 1D simulation results. Numerical dispersion relation is compared to an analytical sharp boundary model [Yañez et al., Phys. Plasmas 18, 052701 (2011)] showing an excellent agreement for the radiation dominated regime of very steep ablation fronts, and the stabilization due to smooth profiles. 2D simulations are presented to validate the numerical self-consistent theory.

Global existence and blowup of a nonlocal problem in space with free boundary

This paper concerns a double fronts free boundary problem for the reaction–diffusion equation with a nonlocal nonlinear reaction term in space. For such a problem, we mainly study the blowup property and global existence of the solutions. Our results show that if the initial value is sufficiently large, then the blowup occurs, while the global fast solution exists for a sufficiently small initial data, and the intermediate case with a suitably large initial data gives the existence of the global slow solution.

Blowup, global fast and slow solutions to a parabolic system with double fronts free boundary

The purpose of this paper is toinvestigate a reaction-diffusion model with double fronts freeboundary. Our approach to the local existence and uniqueness of thesolution is based on the contraction mapping theorem. Also we studythe blowup property of the solution. The result shows that blowupoccurs if the initial datum is large enough. Finallythe long-time behavior of global solutions is presented. It is proved that the solutionis global and fast, which decays uniformly at anexponential rate if the initial datum is small, while there is a global and slow solution provided that the initial value issuitably large.

Linear stability analysis of double ablation fronts in direct-drive inertial confinement fusion

A linear stability theory of double ablation fronts is developed for direct-drive inertial confinement fusion targets. The so-called electron radiative ablation front [S. Fujioka et al., Phys. Rev. Lett. 92, 195001 (2004)] is studied with a self-consistent model. Numerical results are presented as well as an analytical approach for the radiation dominated regime of very steep double ablation front structure. Dispersion relation formula is tackled by means of a sharp boundary model.

Global existence and blowup of a localized problem with free boundary

This paper is concerned with a double fronts free boundary problem for the heat equation with a localized nonlinear reaction term. The local existence and uniqueness of the solution are given by applying the contraction mapping theorem. Then we present some conditions so that the solution blows up in finite time. Finally, the long-time behavior of the global solution is discussed. We show that the solution is global and fast if the initial data is small and that a global slow solution is possible when the initial data is suitably large.

Stability of some stationary solutions to the forced KdV equation with one or two bumps

Free-surface flows past submerged obstacles in a channel are considered. The fluid is assumed to be inviscid and incompressible and the flow to be irrotational. The first-order approximation of long nonlinear surface waves over one or two bumps results in a forced Korteweg–de Vries (fKdV) equation. Solutions of the stationary fKdV equation are constructed and their stability is studied, either analytically or numerically. These various solutions include solitary waves over a single bump, solitary waves with two humps over a double bump, table-top solutions over a double bump and fronts.

Radiation hydrodynamic theory of double ablation fronts in direct-drive inertial confinement fusion

The one-dimensional theory of double ablation fronts is developed for direct-drive inertial confinement fusion targets. The theory is based on the subsonic ablation front approximation and includes the effects of both radiation and electron heat fluxes. It is found that the structure of the ablation front is determined by two dimensionless parameters: the Boltzmann number and the effective mean free path. The Boltzmann number represents the ratio of the convective thermal and radiation energy fluxes, while the effective mean free path is the ratio between the characteristic plasma temperature gradient conduction scale length and the radiation mean free path. The development of a double ablation front is determined based on the range of the above dimensionless parameters. Temperature and density profiles in double ablation fronts are derived from a simplified analytic model and compared with the results of numerical simulations.

Existence of multidimensional shock waves and phase boundaries

In this paper, a kind of Riemann problem for the Euler equations in a van der Waals fluid is considered. We constructed the weak solution in multidimensional space which contains one shock front and one subsonic phase boundary. We mainly follow the arguments of Majda's [A. Majda, The stability of multi-dimensional shock fronts, Mem. Amer. Math. Soc. 275 (1983) 1–95; A. Majda, The existence of multi-dimensional shock fronts, Mem. Amer. Math. Soc. 281 (1983) 1–93] and Métivier's [G. Métivier, Interaction de deux chocs pour un système de deux lois de conservation, en dimension deux d'espace, Trans. Amer. Math. Soc. 296 (1986) 431–479] work. The linear stability results are based on Majda's [A. Majda, The stability of multi-dimensional shock fronts, Mem. Amer. Math. Soc. 275 (1983) 1–95] work for the single shock front and Wang and Xin's [Y.-G. Wang, Z. Xin, Stability and existence of multidimensional subsonic phase transitions, Acta Math. Appl. Sin. 19 (2003) 529–558] work for the single phase boundary. The initial boundary value problem concerned in this paper is different from the boundary value problem for double shock fronts concerned in [G. Métivier, Interaction de deux chocs pour un système de deux lois de conservation, en dimension deux d'espace, Trans. Amer. Math. Soc. 296 (1986) 431–479], we slightly modified Métivier's frame work to establish the existence for the solution to the nonlinear problem.

The thermodynamic and dynamical features of double front structures during 21–31 July 1998 in China

The daily 1° × 1° data of the Aviation (AVN) model, the black body temperature (TBB) data of cloud top, and cloud images by geostationary meteorological satellite (GMS) are used to identify a dew-point front near the periphery of the western Pacific subtropical high (WPSH). The results clearly demonstrate the existence of the dew-point front, and its thermodynamic and dynamic structural characteristics are analyzed in detail. The dew-point front is a transitional belt between the moist southwest monsoon flow and the dry adiabatic sinking flow near the WPSH, manifested by a large horizontal moisture gradient in the mid-lower troposphere and conjugated with the mei-yu front to form a predominant double-front structure associated with intense rainfall in the mei-yu period. The mei-yu front is located between 30° and 35°N, vertically extends from the ground level to the upper level and shifts northward. The dew-point front is to the south of the mei-yu front and lies up against the periphery of the WPSH. Generally, it is located between 850 hPa and 500 hPa. On the dew-point front side, the southwesterly prevails at the lower level and the northeasterly at the upper level; this wind distribution is different from that on the mei-yu front side. Vertical ascending motion exists between the two fronts, and there are descending motions on the north side of the mei-yu front and on the south side of the dew-point front, which form a secondary circulation. The dynamics of the double fronts also have some interesting features. At the lower level, positive vertical vorticity and obvious convergence between the two fronts are clearly identified. At the mid-lower level, negative local change of the divergence (corresponding to increasing convergence) is often embedded in the two fronts or against the mei-yu front. Most cloud clusters occur between the two fronts and propagate down stream in a wave-like manner.

Memory efficient propagation-based watershed and influence zone algorithms for large images

Propagation front or grassfire methods are very popular in image processing because of their efficiency and because of their inherent geodesic nature. However, because of their random-access nature, they are inefficient in large images that cannot fit in available random access memory. We explore ways to increase the memory efficiency of two algorithms that use propagation fronts: the skeletonization by influence zones and the watershed transform. Two algorithms are presented for the skeletonization by influence zones. The first computes the skeletonization on surfaces without storing the enclosing volume. The second performs the skeletonization without any region reference, by using only the propagation fronts. The watershed transform algorithm that was developed keeps in memory the propagation fronts and only one greylevel of the image. All three algorithms use much less memory than the ones presented in the literature so far. Several techniques have been developed in this work in order to minimize the effect of these set operations. These include fast search methods, double propagation fronts, directional propagation, and others.

Acceleration of Typical Atrial Flutter Due to Double-Wave Reentry Induced by Programmed Electrical Stimulation

Acceleration of reentrant tachycardia induced by programmed electrical stimulation is a well-documented phenomenon, but the mechanisms remain poorly understood. Twelve patients with typical atrial flutter were studied. Activation sequence of the underlying reentrant circuit was recorded by multiple multipolar electrodes placed in the right atrium. In five patients, 27 episodes of atrial flutter acceleration were induced by single extrastimuli delivered in the isthmus between the tricuspid annulus and eustachian ridge (TA-ER isthmus) and one by rapid overdrive atrial pacing. Analyses of the activation sequences, intracardiac electrograms, and 12-lead surface ECG P-wave morphology indicated that the acceleration was caused by two successive activation wave fronts circulating in the same direction along the same reentrant circuit (double-wave reentry, DWR). DWR was induced only within a narrow range of coupling interval, from 2 to 45 ms beyond the effective refractory period, and was associated with unidirectional antidromic block of the paced impulse. Patients with DWR had a shorter effective refractory period (138.8+/-13.4 versus 163.8+/-12.2 ms, P<.015) and larger excitable gap (124.0+/-22.6 versus 83.2+/-13.2 ms, P<.009) compared with patients without inducible DWR. All of the DWR episodes were transient. Most (78.6%) terminated after one of the double wave fronts was blocked in the TA-ER isthmus. DWR is one of the mechanisms responsible for programmed electrical stimulation-induced atrial flutter acceleration in human subjects. Its induction requires a sufficient excitable gap and antidromic unidirectional block of the paced impulse in the TA-ER isthmus. In addition, the TA-ER isthmus is the usual site of DWR termination.