Fractional order modeling of large three-dimensional RC networks

An incidence matrix analysis is used to model a three-dimensional network consisting of resistive and capacitive elements distributed across several interconnected layers. A systematic methodology for deriving a descriptor representation of the network with random allocation of the resistors and capacitors is proposed. Using a transformation of the descriptor representation into standard state-space form, amplitude and phase admittance responses of three-dimensional random RC networks are obtained. Such networks display an emergent behavior with a characteristic Jonscher-like response over a wide range of frequencies. A model approximation study of these networks is performed to infer the admittance response using integral and fractional order models. It was found that a fractional order model with only seven parameters can accurately describe the responses of networks composed of more than 70 nodes and 200 branches with 100 resistors and 100 capacitors. The proposed analysis can be used to model charge migration in amorphous materials, which may be associated to specific macroscopic or microscopic scale fractal geometrical structures in composites displaying a viscoelastic electromechanical response, as well as to model the collective responses of processes governed by random events described using statistical mechanics.

Transport in the middle atmosphere

An overview is provided of the current understanding of transport in the middle atmosphere. Over the past quarter century this subject has evolved from a basic recognition of the Brewer-Dobson circulation to a detailed appreciation of many key features of transport such as the stratospheric surf zone, mixing barriers and the dynamics of filamentation. Whilst the elegant theoretical framework for middle atmosphere transport that emerged roughly twenty years ago never fulfilled its promise, useful phenomenological models have been developed together with innovative diagnostic methods. These advances were made possible by the advent of plenty of satellite and aircraft observations of long-lived chemical species together with developments in data assimilation and numerical modeling, and have been driven in large measure by the problem of stratospheric ozone depletion. This review is primarily focused on the stratosphere, where both the interest and the knowledge are the greatest, but a few remarks are also made on the mesosphere.

Planetary-wave-induced transport in the stratosphere

In the stratosphere, chemical tracers are drawn systematically from the equator to the pole. This observed Brewer–Dobson circulation is driven by wave drag, which in the stratosphere arises mainly from the breaking and dissipation of planetary-scale Rossby waves. While the overall sense of the circulation follows from fundamental physical principles, a quantitative theoretical understanding of the connection between wave drag and Lagrangian transport is limited to linear, small-amplitude waves. However, planetary waves in the stratosphere generally grow to a large amplitude and break in a strongly nonlinear fashion. This paper addresses the connection between stratospheric wave drag and Lagrangian transport in the presence of strong nonlinearity, using a mechanistic three-dimensional primitive equations model together with offline particle advection. Attention is deliberately focused on a weak forcing regime, such that sudden warmings do not occur and a quasi-steady state is reached, in order to examine this question in the cleanest possible context. Wave drag is directly linked to the transformed Eulerian mean (TEM) circulation, which is often used as a surrogate for mean Lagrangian motion. The results show that the correspondence between the TEM and mean Lagrangian velocities is quantitatively excellent in regions of linear, nonbreaking waves (i.e., outside the surf zone), where streamlines are not closed. Within the surf zone, where streamlines are closed and meridional particle displacements are large, the agreement between the vertical components of the two velocity fields is still remarkably good, especially wherever particle paths are coherent so that diabatic dispersion is minimized. However, in this region the meridional mean Lagrangian velocity bears little relation to the meridional TEM velocity, and reflects more the kinematics of mixing within and across the edges of the surf zone. The results from the mechanistic model are compared with those from the Canadian Middle Atmosphere Model to test the robustness of the conclusions.

A closer look at chaotic advection in the stratosphere: part I: geometric structure

The relevance of chaotic advection to stratospheric mixing and transport is addressed in the context of (i) a numerical model of forced shallow-water flow on the sphere, and (ii) a middle-atmosphere general circulation model. It is argued that chaotic advection applies to both these models if there is suitable large-scale spatial structure in the velocity field and if the velocity field is temporally quasi-regular. This spatial structure is manifested in the form of “cat’s eyes” in the surf zone, such as are commonly seen in numerical simulations of Rossby wave critical layers; by analogy with the heteroclinic structure of a temporally aperiodic chaotic system the cat’s eyes may be thought of as an “organizing structure” for mixing and transport in the surf zone. When this organizing structure exists, Eulerian and Lagrangian autocorrelations of the velocity derivatives indicate that velocity derivatives decorrelate more rapidly along particle trajectories than at fixed spatial locations (i.e., the velocity field is temporally quasi-regular). This phenomenon is referred to as Lagrangian random strain.

Femininity, feminism and the terrorist

This chapter aims to discuss the relationship between femininity and representations of women involved in violence, focussing on visual representations. Miranda Alison has made the point that the repeated necessity to qualify the term 'combatant' with the descriptor 'female' draws attention to how women soldiers, female freedom fighters, female suicide bombers and female terrorists are exceptional figures. That the female combatant or the female terrorist is an aberration or a deviation from a masculine norm is undermined by the lengthy history of women as warriors, fighters, and terrorists. In that sense it is not so much that fighting women are rare but that there is amnesia within cultural memories concerning the woman fighter. However, in representations of conflict, the dominant image associated with femininity is passive; that is as the defenceless and the defended, or as the allegory of peace. Moreover, representations of men in wars as defeated or wounded means feminising such figures. Miriam Cooke, in her Women and the War Story, 1996, points out how a mythic war story provides men with political roles, in the politikon or public arena, whereas women are domesticated in the space of the oikon. In the mythic war story women may function as Mater Dolorosa, Patriotic Mother or Spartan Mother. It follows then that there are conditions in which it is permissible to represent women fighting on behalf of their children or in defence of the home, and in the absence of men. These images are also found in wider culture: Sarah Connor in Terminator or Ripley in Alien, for example. Images of the female terrorist raise new issues but I want to argue that it is also the case that discussing femininity and the terrorist must involve relating such imagery to representations of the female warrior over a longer timespan. Some questions have shifted since the late twentieth century. Dating from the early 1990s, most Western nations increasingly incorporated women into combat roles within their armed forces. This paper will aim to unpick some of the intricate connections between the increasing presence of women in the armed forces, what relationship this has to emancipation and the participation of women in violence classed as terrorist.

Obesity, diabetes and longevity in the Gulf: is there a Gulf Metabolic Syndrome?

The Gulf is experiencing a pandemic of lifestyle-induced obesity and type 2 diabetes mellitus (T2DM), with rates exceeding 50 and 30%, respectively. It is likely that T2DM represents the tip of a very large metabolic syndrome iceberg, which precedes T2DM by many years and is associated with abnormal/ectopic fat distribution, pathological systemic oxidative stress and inflammation. However, the definitions are still evolving with the role of different fat depots being critical. Hormetic stimuli, which include exercise, calorie restriction, temperature extremes, dehydration and even some dietary components (such as plant polyphenols), may well modulate fat deposition. All induce physiological levels of oxidative stress, which results in mitochondrial biogenesis and increased anti-oxidant capacity, improving metabolic flexibility and the ability to deal with lipids. We propose that the Gulf Metabolic Syndrome results from an unusually rapid loss of hormetic stimuli within an epigenetically important time frame of 2-3 generations. Epigenetics indicates that thriftiness can be programmed by the environment and passed down through several generations. Thus this loss of hormesis can result in continuation of metabolic inflexibility, with mothers exposing the foetus to a milieu that perpetuates a stressed epigenotype. As the metabolic syndrome increases oxidative stress and reduces life expectancy, a better descriptor may therefore be the Lifestyle-Induced Metabolic Inflexibility and accelerated AGEing syndrome – LIMIT-AGE. As life expectancy in the Gulf begins to fall, with perhaps a third of this life being unhealthy – including premature loss of sexual function, it is vital to detect evidence of this condition as early in life as possible. One effective way to do this is by detecting evidence of metabolic inflexibility by studying body fat content and distribution by magnetic resonance (MR). The Gulf Metabolic Syndrome thus represents an accelerated form of the metabolic syndrome induced by the unprecedented rapidity of lifestyle change in the region, the stress of which is being passed from generation to generation and may be accumulative. The fundamental cause is probably due to a rapid increase in countrywide wealth. This has benefited most socioeconomic groups, resulting in the development of an obesogenic environment as the result of the rapid adoption of Western labour saving and stress relieving devices (e.g. cars and air conditioning), as well as the associated high calorie diet.

Wavelet based detection of changes in the composition of RLC networks

The current work discusses the compositional analysis of spectra that may be related to amorphous materials that lack discernible Lorentzian, Debye or Drude responses. We propose to model such response using a 3-dimensional random RLC network using a descriptor formulation which is converted into an input-output transfer function representation. A wavelet identification study of these networks is performed to infer the composition of the networks. It was concluded that wavelet filter banks enable a parsimonious representation of the dynamics in excited randomly connected RLC networks. Furthermore, chemometric classification using the proposed technique enables the discrimination of dielectric samples with different composition. The methodology is promising for the classification of amorphous dielectrics.

Sea level extremes at the coasts of China

Hourly sea level records from 1954 to 2012 at 20 tide gauges at and adjacent to the Chinese coasts are used to analyze extremes in sea level and in tidal residual. Tides and tropical cyclones determine the spatial distribution of sea level maxima. Tidal residual maxima are predominantly determined by tropical cyclones. The 50 year return level is found to be sensitive to the number of extreme events used in the estimation. This is caused by the small number of tropical cyclone events happening each year which lead to other local storm events included thus significantly affecting the estimates. Significant increase in sea level extremes is found with trends in the range between 2.0 and 14.1 mm yr−1. The trends are primarily driven by changes in median sea level but also linked with increases in tidal amplitudes at three stations. Tropical cyclones cause significant interannual variations in the extremes. The interannual variability in the sea level extremes is also influenced by the changes in median sea level at the north and by the 18.6 year nodal cycle at the South China Sea. Neither of PDO and ENSO is found to be an indicator of changes in the size of extremes, but ENSO appears to regulate the number of tropical cyclones that reach the Chinese coasts. Global mean atmospheric temperature appears to be a good descriptor of the interannual variability of tidal residual extremes induced by tropical cyclones but the trend in global temperature is inconsistent with the lack of trend in the residuals.

Spatial and temporal variations of the seasonal sea level cycle in the northwest Pacific

The seasonal sea level variations observed from tide gauges over 1900-2013 and gridded satellite altimeter product AVISO over 1993-2013 in the northwest Pacific have been explored. The seasonal cycle is able to explain 60-90% of monthly sea level variance in the marginal seas, while it explains less than 20% of variance in the eddy-rich regions. The maximum annual and semi-annual sea level cycles (30cm and 6cm) are observed in the north of the East China Sea and the west of the South China Sea respectively. AVISO was found to underestimate the annual amplitude by 25% compared to tide gauge estimates along the coasts of China and Russia. The forcing for the seasonal sea level cycle was identified. The atmospheric pressure and the steric height produce 8-12cm of the annual cycle in the middle continental shelf and in the Kuroshio Current regions separately. The removal of the two attributors from total sea level permits to identify the sea level residuals that still show significant seasonality in the marginal seas. Both nearby wind stress and surface currents can explain well the long-term variability of the seasonal sea level cycle in the marginal seas and the tropics because of their influence on the sea level residuals. Interestingly, the surface currents are a better descriptor in the areas where the ocean currents are known to be strong. Here, they explain 50-90% of inter-annual variability due to the strong links between the steric height and the large-scale ocean currents.