Multilevel maximum likelihood estimation with application to covariance matrices

The asymptotic variance of the maximum likelihood estimate is proved to decrease when the maximization is restricted to a subspace that contains the true parameter value. Maximum likelihood estimation allows a systematic fitting of covariance models to the sample, which is important in data assimilation. The hierarchical maximum likelihood approach is applied to the spectral diagonal covariance model with different parameterizations of eigenvalue decay, and to the sparse inverse covariance model with specified parameter values on different sets of nonzero entries. It is shown computationally that using smaller sets of parameters can decrease the sampling noise in high dimension substantially.     

Flexible work planning of service agents with load balancing

This work emerged from the need to better plan the daily work of 29 travelling service agents, who provide 1090 services to 412 customers in 283 sites, on daily average. A handy and flexible tool was developed and is presented herein. A major contribution of this study is an explicit consideration of the multi-dimensional nature of the problem by the inclusion of workload balancing, which may stand in conflict to cost minimisation. Further, the geographical distribution of the demand is highly irregular. Therefore, two load measures are required and balanced. This required to fitting a proper planning scheme. The planning tool has been applied successfully by the commercial service provider. Improvements in the order of 20% and more were obtained in key performance measures. Moreover, cost reductions, service improvement and load balance were obtained simultaneously: the standard deviations of the service times and working day’s duration were reduced by 18 and 58%, respectively. This enables to reduce the number of agents with no significant harm in performance. Additional practical advantages of the proposed tool are also discussed and demonstrated, for example, the ability to cope with geographical distributions and the flexibility to respond to daily variations in demand.     

The Integration of Tradition and Modernity: A Search for an Urban and Architectural Identity in Arriyadh, The Capital of Saudi Arabia

About 40 years ago, traditional villages, towns and cities of the Arabian Peninsula started to lose their regional characteristics and embody modern forms and shapes. Since then, these characteristics have been subject to dilution due to social and cultural changes as well as institutionalized changes imposed by planning and architectural practices. This process creates debates and clashes between tradition and modernity. Projects carried out since 1975 are the least representative of the regional characteristics but do attempt to have urban and architectural identity. This paper argues that all the actors in “design formulation” (clients, architects, urban designers and planners) are trying to use historic elements in the creation of architectural identities. In fact they are making efforts to create urban and architectural identity to substitute regional characters. These attitudes flourished as a result of dynamic cultural, economic, political and ritualistic influences. This paper highlights the importance of urban and architectural identity in architectural and urban projects in Arriyadh, the capital city of Saudi Arabia because such projects create precedents for other Saudi villages, towns and cities. The study identifies the forces behind the initiation, transformation and evolution of the urban and architectural identity and attempts to supplement scholarship in the fields of architecture, urban design, and planning with regard to the role of identity as a tool for improving the spatial quality of the built environment. Architectural identity participates in setting up meaningful schemata which influences human behavior as a cultural process. The paper supports the concern for search for historic symbols which may influence the architectural identity and the quality of perceived environment during the design process of new or transformed physical environments. The paper views the traditional part of the city as an amalgamation of history and economic interests and its symbolic importance seems to be a perfect place for the emergence of different forms of engagement between tradition and modernity. The importance of the traditional part is unique while the importance of continuity of tradition is very likely complementary.     

The architectural form and landscape as a harmonic entity in the vernacular settlements of Southwestern Saudi Arabia

The paper aims to describe the architectural form and landscape as a harmonic entity in vernacular settlements of southwestern Saudi Arabia. The qualities of vernacular settlements and their integration and responsiveness to the physical, social, economic and cultural environment are demonstrated in this study. The socio-economic activities and customs in southwestern Saudi Arabia are presented as part of the historical process. The paper looks at the major elements of the vernacular villages and landscape as cultural-specific images. While appreciating this, the author laments the way this harmony has been disrupted not least aesthetically as a consequence of modernism which had an impetus on changing life style and social expectation. The cultural-specific images involve direct relationships between the architectural and urban forms as systems and events that are taking place in or around that form. One thesis is that each element of the vernacular village and landscape is linked to an image that shapes and influences human behavior and appreciation, thereby helping to shape larger environmental patterns. Beyond the meaning that specific elements inherit, they have functional and economic values. As a result, their visual qualities are believed to be effective in enhancing behavior through their visual attributes. One of the most important conclusions is that, there are many features of modern village extensions and landscape elements that enhance the interaction with the physical environment that ordinary citizens value, and there are elements of the vernacular villages and landscape that people regret to lose, such as ‘qasabahs', weekly markets, cultivation of terraces, etc. This is inspite of today's, modern planning and design techniques that are being sought to produce new architectural forms and landscape elements. Any attempt to substitute vernacular forms without taking into account the values that the older forms held is considered a failure of adopted modernist attitudes.     

Foraging in the tropics: relationships among species’ abundances,niche asymmetries and body condition in an urban avian assemblage

Two main theories attempt to explain species coexistence: the neutral theory considers all the species as equivalents so biodiversity is mainly regarded as a function of total available resources (i.e. niche expansion), while the niche theory stresses the relevance of differences in niche use between species (i.e. niche packing). The relative importance of these forces is under discussion and has been largely tested in natural ecosystems. However, few studies have addressed this issue in tropical-urban environments. In this work we studied niche overlap asymmetries among the most common urban resident birds, and the effect of habitat type on this pattern, in a subtropical location of South China (Nanning, Guangxi). We found differences in abundances and niche use among species and urban habitats (parks, streets and orchards). We also recorded strong asymmetries in niche use between species, which we divided into three categories: species with positive asymmetries, which showed highly specific niches and were able to exploit other species’ niches; species with neutral asymmetries, which showed high levels of niche overlap with the rest of species; and species with negative asymmetries, which showed low specificity in their niches and were unable to exploit other species’ niches. These differences in niche use correlated with differences in fat scores. Species from the first group showed higher fat scores than other two groups. Ultimately, niche asymmetries correlated with species’ body condition and mediated their differences in abundance, which supports the view that in this urban context niche theory is more appropriate than neutral theory.     

The real cost of growth in Oregon

The costs of growth are little known, poorly understood and typically understated. This study is an initial effort to provide a more complete understanding of the current costs of growth in Oregon. While more than two dozen cost areas are identified, the focus is on basic physical infrastructure required for urban development. A proportionate share costing method is used to determine the public infrastructure costs associated with the construction of a typical single-family house. Each increment of growth is allocated costs for only the increment of system capacity required to serve it. Cost figures are from representative projects recently completed or underway in Oregon. The result is a composite of recent cost data selected to be representative of the state as a whole. An analysis of seven public infrastructure cost areas associated with the construction of a typical single-family house—including public facilities for schools, sewer, storm drainage, roads, water service, parks and recreation, and fire protection—shows that the total cost is about $24,500 per house. Oregon's development impact fees are recovering only a fraction of these costs. As a result, most of these public infrastructure costs are distributed across the entire population of a community through property taxes or general obligation bonds, whereas the benefits of these investments accrue primarily to the new development. The methodology used in this study can be easily replicated and may provide a useful tool for communities trying to obtain better information about the economic and fiscal impacts of urban growth. A review of relevant literature and references are provided.