Jet simulations extending radially self-similar MHD models

We perform a numerical simulation of magnetohydrodynamic radially self-similar jets, whose prototype is the Blandford & Payne analytical example. The reached final steady state is valid close to the rotation axis and also at large distances above the disk where the classical analytical model fails to provide physically acceptable solutions. The outflow starts with a sub-slow magnetosonic speed which subsequently crosses all relevant MHD critical points and corresponding magnetosonic separatrix surfaces. The characteristics are plotted together with the Mach cones and the super-fast magnetosonic outflow satisfies MHD causality. The final solution remains close enough to the analytical one which is thus shown to be topologically stable and robust for various boundary conditions.Comment: 11 pages, 8 figures, minor changes to match the version accepted by MNRA

Bayesian decision making in human collectives with binary choices

Here we focus on the description of the mechanisms behind the process of information aggregation and decision making, a basic step to understand emergent phenomena in society, such as trends, information spreading or the wisdom of crowds. In many situations, agents choose between discrete options. We analyze experimental data on binary opinion choices in humans. The data consists of two separate experiments in which humans answer questions with a binary response, where one is correct and the other is incorrect. The questions are answered without and with information on the answers of some previous participants. We find that a Bayesian approach captures the probability of choosing one of the answers. The influence of peers is uncorrelated with the difficulty of the question. The data is inconsistent with Weber's law, which states that the probability of choosing an option depends on the proportion of previous answers choosing that option and not on the total number of those answers. Last, the present Bayesian model fits reasonably well to the data as compared to some other previously proposed functions although the latter sometime perform slightly better than the Bayesian model. The asset of the present model is the simplicity and mechanistic explanation of the behavior.Comment: 8 pages, 6 figures, 1 tabl

Internal Space for the Noncommutative Geometry Standard Model and Strings

In this paper I discuss connections between the noncommutative geometry approach to the standard model on one side, and the internal space coming from strings on the other. The standard model in noncommutative geometry is described via the spectral action. I argue that an internal noncommutative manifold compactified at the renormalization scale, could give rise to the almost commutative geometry required by the spectral action. I then speculate how this could arise from the noncommutative geometry given by the vertex operators of a string theory.Comment: 1+22 pages. More typos and misprints correcte

Synthetic synchrotron emission maps from MHD models for the jet of M87

We present self-consistent global, steady-state MHD models and synthetic optically thin synchrotron emission maps for the jet of M87. The model consist of two distinct zones: an inner relativistic outflow, which we identify with the observed jet, and an outer cold disk-wind. While the former does not self-collimate efficiently due to its high effective inertia, the latter fulfills all the conditions for efficient collimation by the magneto-centrifugal mechanism. Given the right balance between the effective inertia of the inner flow and the collimation efficiency of the outer disk wind, the relativistic flow is magnetically confined into a well collimated beam and matches the measurements of the opening angle of M87 over several orders of magnitude in spatial extent. The synthetic synchrotron maps reproduce the morphological structure of the jet of M87, i.e. center-bright profiles near the core and limb-bright profiles away from the core. At the same time, they also show a local increase of brightness at some distance along the axis associated to a recollimation shock in the MHD model. Its location coincides with the position of the optical knot HST-1. In addition our best fitting model is consistent with a number of observational constraints such as the magnetic field in the knot HST-1, and the jet-to-counterjet brightness ratio.Comment: 9 pages, 9 figures, accepted by Ap

Titling and beyond: Evidence from Dar es Salaam, Tanzania

Land titling has been a policy priority for developing country cities for decades. In Sub-Saharan Africa and across the world, tenure formalization has been promoted as a tool to improve the quality and value of urban housing. The track record of these projects, however, has generally been disappointing. Why is this? In this paper, we argue that project design has paid too little attention to contextual features of land markets in estimating the benefits of formalization to individual households. We draw on evidence from a case study city – Dar es Salaam, Tanzania – to show that in cities where broader property rights institutions are incomplete and informal sources of tenure security are strong, formal property rights may not be valued by households. This raises questions about the households’ willingness to pay for regularisation and suggests that complementary strategies to build trust in government and consolidate public benefits of titling will be needed to ensure that projects have a beneficial impact

Mathematical Modeling of Two-dimensional Unsteady Flow in Growing Tumor

We investigate the problem of unsteady fluid flow in growing solid tumors. We develop a mathematical model for a growing tumor whose boundary is taken as a sphere, and the unsteady fluid flow within the tumor is assumed to be two dimensional with respect to the radial distance and the latitudinal angle in spherical coordinates. The expressions for the time, radial and latitudinal variations of the flow velocity, pressure, and the two investigated drug concentrations within the tumor were determined analytically. We calculated these quantities in the tumor as well as in a corresponding normal tissue. We find, in particular, that blood pressure in the tumor would be higher than that in the normal tissue, and there could be blood flow circulation in the tumor. For a given spatial location in the tumor, the amount of drug delivered to the growing tumor decreases first with time, but then the rate of decrease reduces with further increase in time. The Therapeutic Index, which is a measure of the efficiency of drug delivery in the tumor in the biomedical science, is determined for different values of the parameters and discussed in the absence or presence of the drugs’ interactions which may exist in the presence of the two drugs in the tumor. The main results of our model agree with the available experiments

Geometric Hamilton-Jacobi Theory

The Hamilton-Jacobi problem is revisited bearing in mind the consequences arising from a possible bi-Hamiltonian structure. The problem is formulated on the tangent bundle for Lagrangian systems in order to avoid the bias of the existence of a natural symplectic structure on the cotangent bundle. First it is developed for systems described by regular Lagrangians and then extended to systems described by singular Lagrangians with no secondary constraints. We also consider the example of the free relativistic particle, the rigid body and the electron-monopole system.Comment: 40 page

RF Power Amplifier Linearization in Professional Mobile Radio Communications Using Artificial Neural Networks

This paper is focused on the linearization of the radio frequency power amplifier of a professional digital handheld by means of an artificial neural network. The simplicity of the neural network that is used, together with the fact that a feedback path is unnecessary, makes this solution ideal to reduce both the cost of a handheld and its hardware complexity, while fully maintaining its performance. A compensation system is also needed to keep the linearization characteristics of the neural network stable against frequency, temperature, and voltage variations. The whole solution that comprises both the neural network and the compensation system has been implemented in the digital signal processor of a real handheld and afterward fully tested. It has proved to be satisfactory to meet the telecommunication standard requirements in all frequency, temperature, and voltage ranges under consideration while efficient to lower the computational cost of the handheld and to make its internal hardware simpler in comparison with other traditional linearization techniques. The results obtained demonstrate that a neural network can be used to linearize the power amplifiers that are used in transmitters of telecommunication equipment, leading to a significant reduction of both their hardware cost and complexity

Production of Nata De Coco Using Soaked Soybean Water as the Alternative Usage of Zwavelzuur Ammoniak (ZA)

Nata de coco is a biomass composed of cellulose, gelatin shaped and white, in which the mass is derived from the fermentation of Acetobacter xylinum in coconut water. During the fermentation, Acetobacter xylinum needs nutrients such as carbon and nitrogen to grow, where the carbon source is obtained from sugar and nitrogen source is obtained from ZA. The recently emerged case regarding the use of ZA fertilizers has raised many polemics in the urban community because of its nature for plants, making it a non food grade products. Therefore the alternative is needed to replace the role of ZA in nata de coco making process. The existence of nitrogen in soaked soybean water from Tempe “Kweni”, an industry in Bantul, has been proven through laboratory results, in which there is a 0,05% content of nitrogen, which had qualified the subtitutes of ZA. Soybean soaked water is also acidic (pH 4-5) so the addition of acetic acid in nata de coco production is unnecessary. The purpose of this study is to determine the formulation of helping materials as a replacement for ZA for making nata de coco, identify the characteristic of nata de coco without ZA from the sensory test results and determine the technical and financial feasibility of nata de coco without ZA production. In this research, trial production of nata de coco without ZA will use 5 variations of waste water concentrations, which is 20%, 25%, 30%, 40% and 50%. Results showed that after 8 days of fermentation the best concentration is obtained from 30% soaked soybean water adding, with 1,2 – 1,3 cm nata thickness. According to sensory response (aroma, texture and flavor) nata de coco without ZA had a better result compared to nata de coco with ZA Keywords: nata de coco, soybean, Zwavelzuur Ammoni