Converging and diverging convection around axisymmetric magnetic flux tubes

A numerical model of idealized sunspots and pores is presented, where axisymmetric cylindrical domains are used with aspect ratios (radius versus depth) up to 4. The model contains a compressible plasma with density and temperature gradients simulating the upper layer of the Sun's convection zone. Non-linear magnetohydrodynamic equations are solved numerically and time-dependent solutions are obtained where the magnetic field is pushed to the centre of the domain by convection cells. This central magnetic flux bundle is maintained by an inner convection cell, situated next to it and with a flow such that there is an inflow at the top of the numerical domain towards the flux bundle. For aspect ratio 4, a large inner cell persists in time, but for lower aspect ratios it becomes highly time dependent. For aspect ratios 2 and 3 this inner convection cell is smaller, tends to be situated towards the top of the domain next to the flux bundle, and appears and disappears with time. When it is gone, the neighbouring cell (with an opposite sense of rotation, i.e. outflow at the top) pulls the magnetic field away from the central axis. As this happens a new inner cell forms with an inflow which pushes the magnetic field towards the centre. This suggests that to maintain their form, both pores and sunspots need a neighbouring convection cell with inflow at the top towards the magnetic flux bundle. This convection cell does not have to be at the top of the convection zone and could be underneath the penumbral structure around sunspots. For an aspect ratio of 1, there is not enough space in the numerical domain for magnetic flux and convection to separate. In this case the solution oscillates between two steady states: two dominant convection cells threaded by magnetic field and one dominant cell that pushes magnetic flux towards the central axis

The role of functional characteristics of commercial streets ininfluencing sense of place in Mosul City Centre

In most cases, changes in the street's uses, types and the streets’ activities may consequently erase what is precious to the users. However, due to insensitive new development within the street has resulted in, the sense of place being disrupted thus, affecting the people’s feelings and perception of the streets. The objective of this paper is to identify the role of the commercial streets in terms of its functional characteristics in giving the sense of place to Mosul City Centre. The case study was conducted in one of the streets in Mosul City Centre, namely; Nineveh Street. A mixed method approach was used in this study which involved 330 respondents to survey questionnaire, 30 respondents for in-depth interviews, field observation, and photographic recordings. The result shows that functional features can be characterized into three main categories i.e. roles, namely social space, cultural space, commercial space, and channel of movements. Each of these categories has an considerable role especially, commercial space in giving the sense of place to Mosul City Centre

Evaluation of the power frequency magnetic field generated by three-core armored cables through 3D finite element simulations

The great expansion in offshore power plants is raising the concern regarding the cumulative effect of the electromagnetic field emissions caused by submarine power cables. In this sense, owners are required to predict these emissions during the permitting and consenting process of new power plants. This is a challenging task, especially in the case of HVAC three-core armored cables due to their complex geometry. Customarily, 2D approaches based on the finite element method (FEM) have been employed for evaluating the magnetic field emissions caused by these cables. However, inaccurate results are obtained since the phase conductors and armor twisting is omitted. This work develops, for the first time in the literature, an in-depth analysis of the magnetic field caused by this type of cable through an ultra-shortened 3D-FEM model, which is also faced to experimental measurements taken on an actual 132 kV, 800 mm2 three-core armored cable. Relevant conclusions are derived regarding the impact of the cable design on the magnetic field emissions, including material properties, as well as single and double-layer armors, presenting the proposed model not only as a valuable tool for predicting purposes, but also for optimizing cable design in terms of magnetic field emissions

Parameterization of ion-induced nucleation rates based on ambient observations

Atmospheric ions participate in the formation of new atmospheric aerosol particles, yet their exact role in this process has remained unclear. Here we derive a new simple parameterization for ion-induced nucleation or, more precisely, for the formation rate of charged 2-nm particles. The parameterization is semi-empirical in the sense that it is based on comprehensive results of one-year-long atmospheric cluster and particle measurements in the size range ~1–42 nm within the EUCAARI (European Integrated project on Aerosol Cloud Climate and Air Quality interactions) project. Data from 12 field sites across Europe measured with different types of air ion and cluster mobility spectrometers were used in our analysis, with more in-depth analysis made using data from four stations with concomitant sulphuric acid measurements. The parameterization is given in two slightly different forms: a more accurate one that requires information on sulfuric acid and nucleating organic vapor concentrations, and a simpler one in which this information is replaced with the global radiation intensity. These new parameterizations are applicable to all large-scale atmospheric models containing size-resolved aerosol microphysics, and a scheme to calculate concentrations of sulphuric acid, condensing organic vapours and cluster ions

Geophysical applicability of atomic clocks: direct continental geoid mapping

The geoid is the true physical figure of the Earth, a particular equipotential surface of the Earth's gravity field that accounts for the effect of all subsurface density variations. Its shape approximates best (in the sense of least squares) the mean level of oceans, but the geoid is more difficult to determine over continents. Satellite missions carry out distance measurements and derive the gravity field to provide geoid maps over the entire globe. However, they require calibration and extensive computations including integration, which is a non-unique operation. Here we propose a direct method and a new tool that directly measures geopotential differences on continents using atomic clocks. General relativity theory predicts constant clock rate at sea level, and faster (slower) clock rate above (below) sea level. The technology of atomic clocks is on the doorstep of reaching an accuracy level in clock rate (frequency ratio inaccuracy of 10−18), which is equivalent to 1 cm in determining equipotential surface (including geoid) height. We discuss the value and future applicability of such measurements including direct geoid mapping on continents, and joint gravity-geopotential surveying to invert for subsurface density anomalies. Our synthetic calculations show that the geoid perturbation caused by a 1.5-km radius sphere with 20 per cent density anomaly buried at 2-km depth in the Earth's crust is already detectable by atomic clocks of achievable accuracy. Therefore atomic clock geopotential surveys, used together with relative gravity data to benefit from their different depth sensitivities, can become a useful tool in mapping density anomalies within the Eart

Beyond information: factors in participation in networks of practice, a case study of web management in UK Higher Education

Purpose To explore the pattern and significance of cross-organizational ties in an emergent professional field, web production in UK Higher Education. Methodology/Approach The research is based on in-depth interviews with 21 practitioners and analysis of activity in cross-organizational spaces, such as an online community and a series of annual practitioner conferences on the web in HE (1997-). Findings The cross organizational spaces have support and symbolic roles as well as informational ones. They have overlapping but different membership and agendas. Key factors that govern individual participation and so the shape of cross-organizational spaces are differential involvement in technical innovation, degree of organizational embedding or marginality, differences in organizational position and role, orientation towards centralisation or decentralisation and orientation towards marketing or IT. There is some sense of occupational community among web managers, but within that also diversity and a significant fracture line between marketing and IT perspectives on the role. This may explain the lack of formal professionalization. As a more natural boundary practice between organizations than marketing, IT has more public visibility, possibly influencing the course jurisdictional struggles over who should control the web. Research limitations/implications As a heavily contextualised study, its detail reflects particular features of HE in the UK at one period as well as specific aspects of the web as a technology. Nevertheless, underlying factors which seem to influence participation and non-participation in cross-organizational networks may be generalisable to many occupations, particularly where knowledge is rapidly changing. Practical implications Some suggestions about how cross-organizational knowledge sharing is most effectively supported can be derived from the analysis. IT is a natural focus for cooperation, but there is a risk of this masking the importance of other professional practices. Efforts at formal professionalization may be devisive because people have different professional ambitions and there are individual and organizational benefits in not professionalizing the role formally. New practitioners may be the most active in using extra-organizational networks to assist them to become more embedded locally. Old hands, though they have high prestige and centrality, may increasingly take their own path away from the community. Aspects of local roles such as involvement in innovation or decentralist strategies favour participation in cross-organizational networks. Originality/value of paper Most studies of knowledge sharing have focussed on the factors which influence it within an organization, yet cross-organizational sharing is also of importance, even for established professions as the boundaries of organizations become more open. For new occupations cross-organizational ties may be a critical resource, and not only for sharing information or support, but for making sense of what the job is about at the deepest level. The research is also original in analysing a relatively little researched occupational group, those producing web sites for a living. It will be relevant to those interested in online and people centred information seeking, in professionalization and occupational identity

Prediction of unsupported excavations behaviour with machine learning techniques

Artificial intelligence and machine learning algorithms have known an increasing interest from the research community, triggering new applications and services in many domains. In geotechnical engineering, for instance, neural networks have been used to benefit from information gained at a given site in order to extract relevant constitutive soil information from field measurements [1]. The goal of this work is to use machine (supervised) learning techniques in order to predict the behaviour of a sheet pile wall excavation, minimizing a loss function that maps the input (excavation’s depth, soil’s characteristics, wall’s stiffness) to a predicted output (wall’s deflection, soil’s settlement, wall’s bending moment). Neural networks are used to do this supervised learning. A neural network is composed of neurons which apply a mathematical function on their input (see Figure 1, left) and synapses which take the output of one neuron to the input of another one. For our purpose, neural networks can be understood as a set of nonlinear functions which can be fitted to data by changing their parameters. In this work, a simple class of neural networks, called Multi-Layer Perceptron (MLP) are used. They are composed of an input layer of neurons, an output layer, and one or several middle layers (hidden layers) (see Figure 1, right). A neural network learns by adjusting the weights and biases in order to minimize a certain loss function (for instance: the mean squared error) between the desired and the predicted output. Stochastic gradient descent or one of its variations are used to adjust the parameters and the gradients are obtained through backpropagation (an efficient application of the chain rule). The interest in neural networks comes from the fact that they are universal function estimators, in the sense that they can approximate any continuous function to any precision given enough neurons. However, this can lead to over-fitting problems where the network learns the noise in the data, or worse, where they memorize by rote each sample [2]