Numerical representation of internal waves propagation

Similar to surface waves propagating at the interface of two fluid of different densities (like air and water), internal waves in the oceanic interior travel along surfaces separating waters of different densities (e.g. at the thermocline). Due to their key role in the global distribution of (physical) diapycnal mixing and mass transport, proper representation of internal wave dynamics in numerical models should be considered a priority since global climate models are now configured with increasingly higher horizontal/vertical resolution. However, in most state-of-the-art oceanic models, important terms involved in the propagation of internal waves (namely the horizontal pressure gradient and horizontal divergence in the continuity equation) are generally discretized using very basic numerics (i.e. second-order approximations) in space and time. In this paper, we investigate the benefits of higher-order approximations in terms of the discrete dispersion relation (in the linear theory) on staggered and nonstaggered computational grids. A fourth-order scheme discretized on a C-grid to approximate both pressure gradient and horizontal divergence terms provides clear improvements but, unlike nonstaggered grids, prevents the use of monotonic or non- oscillatory schemes. Since our study suggests that better numerics is required, second and fourth order direct space-time algorithms are designed, thus paving the way toward the use of efficient high-order discretizations of internal gravity waves in oceanic models, while maintaining good sta- bility properties (those schemes are stable for Courant numbers smaller than 1). Finally, important results obtained at a theoretical level are illustrated at a discrete level using two-dimensional (x,z) idealized experiments

Unlocking Structure-Self-Assembly Relationships in Cationic Azobenzene Photosurfactants.

Azobenzene photosurfactants are light-responsive amphiphiles that have garnered significant attention for diverse applications including delivery and sorting systems, phase transfer catalysis, and foam drainage. The azobenzene chromophore changes both its polarity and conformation (trans-cis isomerization) in response to UV light, while the amphiphilic structure drives self-assembly. Detailed understanding of the inherent relationship between the molecular structure, physicochemical behavior, and micellar arrangement of azobenzene photosurfactants is critical to their usefulness. Here, we investigate the key structure-function-assembly relationships in the popular cationic alkylazobenzene trimethylammonium bromide (AzoTAB) family of photosurfactants. We show that subtle changes in the surfactant structure (alkyl tail, spacer length) can lead to large variations in the critical micelle concentration, particularly in response to light, as determined by surface tensiometry and dynamic light scattering. Small-angle neutron scattering studies also reveal the formation of more diverse micellar aggregate structures (ellipsoids, cylinders, spheres) than predicted based on simple packing parameters. The results suggest that whereas the azobenzene core resides in the effective hydrophobic segment in the trans-isomer, it forms part of the effective hydrophilic segment in the cis-isomer because of the dramatic conformational and polarity changes induced by photoisomerization. The extent of this shift in the hydrophobic-hydrophilic balance is determined by the separation between the azobenzene core and the polar head group in the molecular structure. Our findings show that judicious design of the AzoTAB structure enables selective tailoring of the surfactant properties in response to light, such that they can be exploited and controlled in a reliable fashion

A reduced-order strategy for 4D-Var data assimilation

This paper presents a reduced-order approach for four-dimensional variational data assimilation, based on a prior EO F analysis of a model trajectory. This method implies two main advantages: a natural model-based definition of a mul tivariate background error covariance matrix $\textbf{B}_r$, and an important decrease of the computational burden o f the method, due to the drastic reduction of the dimension of the control space. % An illustration of the feasibility and the effectiveness of this method is given in the academic framework of twin experiments for a model of the equatorial Pacific ocean. It is shown that the multivariate aspect of $\textbf{B}_r$ brings additional information which substantially improves the identification procedure. Moreover the computational cost can be decreased by one order of magnitude with regard to the full-space 4D-Var method

Light-responsive self-assembly of a cationic azobenzene surfactant at high concentration.

The formation of high-concentration mesophases by a cationic azobenzene photosurfactant is described for the first time. Using a combination of polarised optical microscopy and small-angle X-ray scattering, optically anisotropic, self-assembled structures with long-range order are reported. The mesophases are disrupted or lost upon UV irradiation

A single-component photorheological fluid with light-responsive viscosity.

Viscoelastic fluids whose rheological properties are tunable with light have the potential to deliver significant impact in fields relying on a change in flow behavior, such as in-use tuning of combined efficient heat-transfer and drag-reduction agents, microfluidic flow and controlled encapsulation and release. However, simple, single-component systems must be developed to allow integration with these applications. Here, we report a single-component viscoelastic fluid, capable of a dramatic light-sensitive rheological response, from a neutral azobenzene photosurfactant, 4-hexyl-4'butyloxymonotetraethylene glycol (C6AzoOC4E4) in water. From cryo-transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and rheology measurements, we observe that the photosurfactant forms an entangled network of wormlike micelles in water, with a high viscosity (28 Pa s) and viscoelastic behaviour. UV irradiation of the surfactant solution creates a less dense micellar network, with some vesicle formation. As a result, the solution viscosity is reduced by four orders of magnitude (to 1.2 × 10-3 Pa s). This process is reversible and the high and low viscosity states can be cycled several times, through alternating UV and blue light irradiation

Physics–Dynamics Coupling in weather, climate and Earth system models: Challenges and recent progress

This is the final version. Available from American Meteorological Society via the DOI in this record.Numerical weather, climate, or Earth system models involve the coupling of components. At a broad level, these components can be classified as the resolved fluid dynamics, unresolved fluid dynamical aspects (i.e., those represented by physical parameterizations such as subgrid-scale mixing), and nonfluid dynamical aspects such as radiation and microphysical processes. Typically, each component is developed, at least initially, independently. Once development is mature, the components are coupled to deliver a model of the required complexity. The implementation of the coupling can have a significant impact on the model. As the error associated with each component decreases, the errors introduced by the coupling will eventually dominate. Hence, any improvement in one of the components is unlikely to improve the performance of the overall system. The challenges associated with combining the components to create a coherent model are here termed physics–dynamics coupling. The issue goes beyond the coupling between the parameterizations and the resolved fluid dynamics. This paper highlights recent progress and some of the current challenges. It focuses on three objectives: to illustrate the phenomenology of the coupling problem with references to examples in the literature, to show how the problem can be analyzed, and to create awareness of the issue across the disciplines and specializations. The topics addressed are different ways of advancing full models in time, approaches to understanding the role of the coupling and evaluation of approaches, coupling ocean and atmosphere models, thermodynamic compatibility between model components, and emerging issues such as those that arise as model resolutions increase and/or models use variable resolutions.Natural Environment Research Council (NERC)National Science FoundationDepartment of Energy Office of Biological and Environmental ResearchPacific Northwest National Laboratory (PNNL)DOE Office of Scienc

Parent satisfaction with the Loire Infant Follow-up Team (LIFT) premature and at-risk infant network in the Pays-de-la-Loire area (France)

BACKGROUND: The Loire Infant Follow-up Team (LIFT) is a network for caring for premature infants whose gestational age is 34 WA or less and at-risk neonates in the Pays-de-la-Loire area in France. The network aims to screen for clinical anomalies early and to propose adapted care. Trained physicians follow the included children in a standardized manner at 3, 6, 9, 12, and 18 months and 2 years, with a specific examination by psychologists at 2 years. The aim of the study was to assess the satisfaction of the parents of the children followed.METHODS: To evaluate parent satisfaction, a questionnaire from the Consumer Satisfaction Survey (CSS) in its French version was sent to parents whose infants were 2 years old, stratifying on the presence of an anomaly. The questioner had 39 items, with 8 specific items on the network and 31 from the CSS. The questionnaire was mailed twice in September 2006. RESULTS: Out of 300 questionnaires mailed, 269 were returned (rate 89.7 %). The questionnaire was assessed using principal component analysis with 2 dimensions for the 30 items common to all children, one of which covered empathy with physicians and the other with the consulting psychologists at 2 years. The validity was good (Cronbach coefficient, 0.91). The answers to overall questions such as "We are satisfied with the care in the network" scored 16.1±0.7/20, with 90 % "totally agree" or "moderately agree" responses. The "The care is perfect" scored 14.6±0.7/20 with 78 % agreeing with the statement. The total score for 30 general questions was 14.6±3.1 (median, 14.9). The total score was lower for infants with anomalies: 13.7±3.3 versus 14.9±2.9 (P<0.01). The answers with a low score (<10) were given by 22 parents (8.2 %). There was no significant relation between the total score or the satisfaction score and neonatal events. CONCLUSION: A postal survey is helpful to know the views of parents on the follow-up of their infants. This good level of satisfaction seems to stem from the parents feeling they belong to the network, the quality of the relationships with personnel, and the doctors\u27 empathy, as well as the number of contacts between parents and the network coordinator

Piston-driven numerical wave tank based on WENO solver of well-balanced shallow water equations

A numerical wave tank equipped with a piston type wave-maker is presented for long-duration simulations of long waves in shallow water. Both wave maker and tank are modelled using the nonlinear shallow water equations, with motions of the numerical piston paddle accomplished via a linear mapping technique. Three approaches are used to increase computational efficiency and accuracy. First, the model satisfies the exact conservation property (C-property), a stepping stone towards properly balancing each term in the governing equation. Second, a high-order weighted essentially non-oscillatory (WENO) method is used to reduce accumulation of truncation error. Third, a cut-off algorithm is implemented to handle contaminated digits arising from round-off error. If not treated, such errors could prevent a numerical scheme from satisfying the exact C-property in long-duration simulations. Extensive numerical tests are performed to examine the well-balanced property, high order accuracy, and shock-capturing ability of the present scheme. Correct implementation of the wave paddle generator is verified by comparing numerical predictions against analytical solutions of sinusoidal, solitary, and cnoidal waves. In all cases, the model gives satisfactory results for small-amplitude, low frequency waves. Error analysis is used to investigate model limitations and derive a user criterion for long wave generation by the model