4,757 research outputs found
Measuring the Size of the Informal Economy: A Critical Review
There has been a burgeoning number of studies attempting to measure the size of the ‘black’ economy. These are based on a variety of methodologies and provide a range of estimates, not just across countries but also within the same countries and often by the same author(s). This raises a number of issues: What is meant by the term ‘black’ economy? Is it an appropriate description? What, if any, is the theory underlying the estimates of informal economic activity? This paper examines these and other issues, and concludes that whilst the existence of what we prefer to call the ‘informal’ or ‘grey’ economy in most countries is incontrovertible, there is a lack of consensus on the appropriate methodology for estimating its size. More importantly, the large number of studies so far are simply exercises in measurement without theory, though we are sceptical that even with strong theoretical underpinnings it is possible to provide accurate estimates of a complicated web of informal activities.Informal, grey and black economy, tax evasion, criminal activities
Production of non-Abelian tensor gauge bosons. Tree amplitudes in generalized Yang-Mills theory and BCFW recursion relation
The BCFW recursion relation allows to calculate tree-level scattering
amplitudes in generalized Yang-Mills theory and, in particular, four-particle
amplitudes for the production rate of non-Abelian tensor gauge bosons of
arbitrary high spin in the fusion of two gluons. The consistency of the
calculations in different kinematical channels is fulfilled when all
dimensionless cubic coupling constants between vector bosons (gluons) and high
spin non-Abelian tensor gauge bosons are equal to the Yang-Mills coupling
constant. There are no high derivative cubic vertices in the generalized
Yang-Mills theory. The amplitudes vanish as complex deformation parameter tends
to infinity, so that there is no contribution from the contour at infinity. We
derive a generalization of the Parke-Taylor formula in the case of production
of two tensor gauge bosons of spin-s and N gluons (jets). The expression is
holomorhic in the spinor variables of the scattered particles, exactly as the
MHV gluon amplitude is, and reduces to the gluonic MHV amplitude when s=1. In
generalized Yang-Mills theory the tree level n-particle scattering amplitudes
with all positive helicities vanish, but tree amplitudes with one negative
helicity particle are already nonzero.Comment: 19 pages, LaTex fil
Urban encounters: juxtapositions of difference and the communicative interface of global cities
This article explores the communicative interface of global cities, especially as it is shaped in the juxtapositions of difference in culturally diverse urban neighbourhoods. These urban zones present powerful examples, where different groups live cheek by jowl, in close proximity and in intimate interaction — desired or unavoidable. In these urban locations, the need to manage difference is synonymous to making them liveable and one's own. In seeking (and sometimes finding) a location in the city and a location in the world, urban dwellers shape their communication practices as forms of everyday, mundane and bottom-up tactics for the management of diversity. The article looks at three particular areas where cultural diversity and urban communication practices come together into meaningful political and cultural relations for a sustainable cosmopolitan life: citizenship, imagination and identity
The Underground Economy: An Overview and Estimates for Cyprus
The paper begins by describing three important macroeconomic approaches to the measurement of the underground economy. Estimates of the size of the underground economy in Cyprus are then discussed. The estimates are derived using a method first applied by Tanzi to data for the United States. Using annual times series data for the period 1960-1990 the size of the underground economy in Cyprus is estimated to be, approximately, between 3% and 10% of GNP.
A multi-sensor data-driven methodology for all-sky passive microwave inundation retrieval
We present a multi-sensor Bayesian passive microwave retrieval algorithm for
flood inundation mapping at high spatial and temporal resolutions. The
algorithm takes advantage of observations from multiple sensors in optical,
short-infrared, and microwave bands, thereby allowing for detection and mapping
of the sub-pixel fraction of inundated areas under almost all-sky conditions.
The method relies on a nearest-neighbor search and a modern sparsity-promoting
inversion method that make use of an a priori dataset in the form of two joint
dictionaries. These dictionaries contain almost overlapping observations by the
Special Sensor Microwave Imager and Sounder (SSMIS) on board the Defense
Meteorological Satellite Program (DMSP) F17 satellite and the Moderate
Resolution Imaging Spectroradiometer (MODIS) on board the Aqua and Terra
satellites. Evaluation of the retrieval algorithm over the Mekong Delta shows
that it is capable of capturing to a good degree the inundation diurnal
variability due to localized convective precipitation. At longer timescales,
the results demonstrate consistency with the ground-based water level
observations, denoting that the method is properly capturing inundation
seasonal patterns in response to regional monsoonal rain. The calculated
Euclidean distance, rank-correlation, and also copula quantile analysis
demonstrate a good agreement between the outputs of the algorithm and the
observed water levels at monthly and daily timescales. The current inundation
products are at a resolution of 12.5 km and taken twice per day, but a higher
resolution (order of 5 km and every 3 h) can be achieved using the same
algorithm with the dictionary populated by the Global Precipitation Mission
(GPM) Microwave Imager (GMI) products.Comment: 12 pages, 9 Figure
Window functions and sigmoidal behaviour of memristive systems
Summary: A common approach to model memristive systems is to include empirical window functions to describe edge effects and nonlinearities in the change of the memristance. We demonstrate that under quite general conditions, each window function can be associated with a sigmoidal curve relating the normalised time-dependent memristance to the time integral of the input. Conversely, this explicit relation allows us to derive window functions suitable for the mesoscopic modelling of memristive systems from a variety of well-known sigmoidals. Such sigmoidal curves are defined in terms of measured variables and can thus be extracted from input and output signals of a device and then transformed to its corresponding window. We also introduce a new generalised window function that allows the flexible modelling of asymmetric edge effects in a simple manner
Colocation and role of polyphosphates and alkaline phosphatase in apatite biomineralization of elasmobranch tesserae
AbstractElasmobranchs (e.g. sharks and rays), like all fishes, grow continuously throughout life. Unlike other vertebrates, their skeletons are primarily cartilaginous, comprising a hyaline cartilage-like core, stiffened by a thin outer array of mineralized, abutting and interconnected tiles called tesserae. Tesserae bear active mineralization fronts at all margins and the tesseral layer is thin enough to section without decalcifying, making this a tractable but largely unexamined system for investigating controlled apatite mineralization, while also offering a potential analog for endochondral ossification. The chemical mechanism for tesserae mineralization has not been described, but has been previously attributed to spherical precursors, and alkaline phosphatase (ALP) activity. Here, we use a variety of techniques to elucidate the involvement of phosphorus-containing precursors in the formation of tesserae at their mineralization fronts. Using Raman spectroscopy, fluorescence microscopy and histological methods, we demonstrate that ALP activity is located with inorganic phosphate polymers (polyP) at the tessera–uncalcified cartilage interface, suggesting a potential mechanism for regulated mineralization: inorganic phosphate (Pi) can be cleaved from polyP by ALP, thus making Pi locally available for apatite biomineralization. The application of exogenous ALP to tissue cross-sections resulted in the disappearance of polyP and the appearance of Pi in uncalcified cartilage adjacent to mineralization fronts. We propose that elasmobranch skeletal cells control apatite biomineralization by biochemically controlling polyP and ALP production, placement and activity. Previous identification of polyP and ALP shown previously in mammalian calcifying cartilage supports the hypothesis that this mechanism may be a general regulating feature in the mineralization of vertebrate skeletons
Variational Data Assimilation via Sparse Regularization
This paper studies the role of sparse regularization in a properly chosen
basis for variational data assimilation (VDA) problems. Specifically, it
focuses on data assimilation of noisy and down-sampled observations while the
state variable of interest exhibits sparsity in the real or transformed domain.
We show that in the presence of sparsity, the -norm regularization
produces more accurate and stable solutions than the classic data assimilation
methods. To motivate further developments of the proposed methodology,
assimilation experiments are conducted in the wavelet and spectral domain using
the linear advection-diffusion equation
Architectural privacy: a topological approach to relational design problems
This work studies the abstract architectural quality of privacy as presented in enclosed, border-defined space. Furthermore, a programming environment (processing programming language) is implemented as to evaluate given architectural plans and generate conceptual topological diagrams indicating the relation of spaces according to a set or desired degree of privacy. These abstract topological diagrams could then be enriched and implemented as analytic or synthetic means for documentation or experimentation in certain socio-cultural
contexts
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