A novel repair model for imperfect maintenance

The basic repair rate models for repairable systems may be homogeneous Poisson processes, renewal processes or nonhomogeneous Poisson processes. In addition to these models, geometric processes are studied occasionally. Geometric processes, however, can only model systems with monotonously changing (increasing, decreasing or constant) failure intensity. This paper deals with the reliability modelling of the failure process of repairable systems when the failure intensity shows a bathtub type non-monotonic behaviour. A new stochastic process, an extended Poisson process, is introduced. Reliability indices and parameter estimation are presented. A comparison of this model with other repair models based on a dataset is made.

Experimental model of the interfacial instability in aluminium reduction cells

A solution has been found to the long-standing problem of experimental modelling of the interfacial instability in aluminium reduction cells. The idea is to replace the electrolyte overlaying molten aluminium with a mesh of thin rods supplying current down directly into the liquid metal layer. This eliminates electrolysis altogether and all the problems associated with it, such as high temperature, chemical aggressiveness of media, products of electrolysis, the necessity for electrolyte renewal, high power demands, etc. The result is a room temperature, versatile laboratory model which simulates Sele-type, rolling pad interfacial instability. Our new, safe laboratory model enables detailed experimental investigations to test the existing theoretical models for the first time.

Asymptotic expansions for Taylor coefficients of the composition of two functions

We give an asymptotic expansion for the Taylor coe±cients of L(P(z)) where L(z) is analytic in the open unit disc whose Taylor coe±cients vary `smoothly' and P(z) is a probability generating function. We show how this result applies to a variety of problems, amongst them obtaining the asymptotics of Bernoulli transforms and weighted renewal sequences.

Tephra fallout hazard assessment for a Plinian eruption scenario at Volcán de Colima (Mexico)

Volcanic ash fallout associated with renewal of explosive activity at Colima, represents a serious threat to the surrounding urbanized area. Here we assess the tephra fallout hazard associated with a Plinian eruption scenario. The eruptive history of Volcán de Colima shows that Plinian eruptions occur approximately every 100 years and the last eruption, the 1913, represents the largest historic eruption of this volcano. We used the last eruption as a reference to discuss volcanic hazard and risk scenarios connected with ash fallout. Tephra fallout deposits are modeled using HAZMAP, a model based on a semi-analytical solution of the advection– diffusion–sedimentation equation for volcanic particles. Based on a statistical study of wind profiles at Colima region, we first reconstructed ash loading maps and then computed ground load probability maps for different seasons. The obtained results show that a Plinian eruptive scenario at Volcán de Colima, could seriously damage more than 10 small towns and ranches, and potentially affect big cities located at tens of kilometers from the eruptive center. The probability maps obtained are aimed to give support to the risk mitigation strategies

Community involvement in urban design: help or hindrance?

This paper examines the realities of community involvement in urban design in the context of a study of the West Itchen Neighbourhood of Southampton, a diverse inner city area accommodating some 7,000 households and 18,000 people. The findings are based on a literature review of community involvement in urban design and case study research into three government supported regeneration projects all located within the study area: a Neighbourhood Renewal Area - designated in 1994; an Estate Action Scheme - implemented between 1993 and 1996; and a Single Regeneration Budget programme - following a successful bid in 1995. The research was undertaken by Helen Gregory in 1997/8 as the basis of a dissertation, supervised by Alan Rowley, submitted for the award of an MPhil in Environmental Planning and Development from The University of Reading.

The story of Temple Bar: creating Dublin's cultural quarter

The paper conceptualises and explores the links between cities, commerce, urbanism and cultural planning by drawing on Temple Bar in Dublin as an example of how, by linking these concepts to practice in real concrete situations urban life or urban culture can be created and/or revitalised. Temple Bar is Dublin's emerging cultural quarter, an experiment in urban revitalisation which is deliberately focused on culture and urbanism as ways of rediscovering the good city. It has attracted considerable interest from across Europe, and has secured EC funding to kick-start the process of renewal. The author was appointed by the Irish Government to prepare the area management and development strategy for Temple Bar in 1990. Wary of the dangers of property led regeneration, of the destructive impacts of sudden or cataclysmic change, the agencies in Temple Bar have deliberately adopted a strategic management approach to the area. This is referred to as 'urban stewardship', a process of looking after and respecting a place, and helping it to help itself. The paper explores whether there is a 'culture of cities' and whether it is possible to recreate an urban culture. Following Raymond Williams, an anthropological definition of culture is employed, "... a particular way of life, which expresses certain meaning and values not only in art and learning but also in institutional and ordinary behaviour". Rather than being simply an add-on to the serious concerns of economic development and the built environment, culture has both helped shape, and continues to develop in, the streets, spaces and buildings of the city.

Hyperactive governance in the Thames Gateway

This paper examines the implementation of brownfield regeneration policies in the UK within the context of complex systems of multi-level governance. Using the regeneration of the Thames Gateway as an example, it explores how the Government's centrally driven institutional arrangements have undermined leadership in this key development project. The Government's approach to brownfield governance is characterised as one of constant intervention in the Thames Gateway in an ad hoc and incoherent fashion. Congested and fragmented governance structures are the result. These, this paper argues, have diffused the focus and undermined the leadership of policy and implementation. It is suggested that the adoption of the principles of policy mapping and weaving would bring more clarity and coherence to the governance of the Thames Gateway.

Smoothness of scale functions for spectrally negative Lévy processes

Scale functions play a central role in the fluctuation theory of spectrally negative Lévy processes and often appear in the context of martingale relations. These relations are often require excursion theory rather than Itô calculus. The reason for the latter is that standard Itô calculus is only applicable to functions with a sufficient degree of smoothness and knowledge of the precise degree of smoothness of scale functions is seemingly incomplete. The aim of this article is to offer new results concerning properties of scale functions in relation to the smoothness of the underlying Lévy measure. We place particular emphasis on spectrally negative Lévy processes with a Gaussian component and processes of bounded variation. An additional motivation is the very intimate relation of scale functions to renewal functions of subordinators. The results obtained for scale functions have direct implications offering new results concerning the smoothness of such renewal functions for which there seems to be very little existing literature on this topic.

(Non)differentiability and asymptotics for potential densities of subordinators

For subordinators with positive drift we extend recent results on the structure of the potential measures and the renewal densities. Applying Fourier analysis a new representation of the potential densities is derived from which we deduce asymptotic results and show how the atoms of the Lévy measure translate into points of (non)differentiability of the potential densities.

Venues on the verges: London's theater government between 1594 and 1614

In 1594, major decisions were made by the governors of London and the country about plays and playing. We need to learn what lay behind these events, such as what led James Burbage to build his Blackfriars theater in 1596. That initial fiasco might tell us much about what lay behind Shakespeare’s decision to join the new Chamberlain’s Men in 1594 and his subsequent commitment to them as a full-time playwright. When the Globe burned down in 1613, a majority of the shareholders decided to rebuild it at great cost, but Shakespeare withdrew. The rebuilding was old-fashioned thinking, reverting to the company’s desire, asserted in 1594, to play indoors in winter, which helps to clarify their decisions and Shakespeare’s own—to write plays rather than more long poems. The few surviving papers of the Privy Council and the London mayoralty from the time suggest that one of the two new companies of 1594 preferred to play indoors during the winter instead of at their allocated open playhouses in the suburbs. They tried to renew this traditional practice, first in 1594 and again in 1596 when James Burbage built the indoor Blackfriars playhouse for them. The renewal of the Globe in 1614 was part of the same thinking, although Shakespeare evidently opted out of the decision.

Treating the Tenant as a Customer: can good service improve real estate performance?

Customer Relationship Management (CRM) theory suggests that good customer service results in satisfied customers, who in turn are more likely to remain loyal and recommend the service provider to others. Applied to real estate, this theory implies that landlords should see a return on any investment in the service they give to tenants, in the form of increased lease renewal rates and fewer void periods, achieved without compromising rents. This paper examines determinants of occupier satisfaction, and investigates the relationship between occupier satisfaction and property performance, using measures such as capital growth, income return, lease renewal rates and total return. The analysis is based upon a pilot study using occupier satisfaction responses from around 2500 interviewees based in multi-tenanted offices, shopping centres and retail warehouses on out-of-town retail parks in the UK. The analysis is being extended to cover a larger sample for the author’s PhD. Part 1 of the analysis examines occupier satisfaction, whilst Part 2 considers its impact on property performance.

Nuclear Factor-kappaB controls the reaggregation of 3D neurosphere cultures in vitro

The approach of reaggregation involves the regeneration and self-renewal of histotypical 3D spheres from isolated tissue kept in suspension culture. Reaggregated spheres can be used as tumour, genetic, biohybrid and neurosphere models. In addition the functional superiority of 3D aggregates over conventional 2D cultures developed the use of neurospheres for brain engineering of CNS diseases. Thus 3D aggregate cultures created enormous interest in mechanisms that regulate the formation of multicellular aggregates in vitro. Here we analyzed mechanisms guiding the development of 3D neurosphere cultures. Adult neural stem cells can be cultured as self-adherent clusters, called neurospheres. Neurospheres are characterised as heterogeneous clusters containing unequal stem cell sub-types. Tumour necrosis factor-alpha (TNF-alpha is one of the crucial inflammatory cytokines with multiple actions on several cell types. TNF-alpha strongly activates the canonical Nuclear Factor Kappa-B (NF- kappaB) pathway. In order to investigate further functions of TNF in neural stem cells (NSCs) we tested the hypothesis that TNF is able to modulate the motility and/or migratory behaviour of SVZ derived adult neural stem cells. We observed a significantly faster sphere formation in TNF treated cultures than in untreated controls. The very fast aggregation of isolated NSCs (<2h) is a commonly observed phenomenon, though the mechanisms of 3D neurosphere formation remain largely unclear. Here we demonstrate for the first time, increased aggregation and enhanced motility of isolated NSCs in response to the TNF-stimulus. Moreover, this phenomenon is largely dependent on activated transcription factor NF-kappaB. Both, the pharmacological blockade of NF-kappaB pathway by pyrrolidine dithiocarbamate (PDTC) or Bay11-7082 and genetic blockade by expression of a transdominant-negative super-repressor IkappaB-AA1 led to decreased aggregation.

Neural stem cells, inflammation and NF-kappaB: basic principle of maintenance and repair or origin of brain tumours?

Several recent reports suggest that inflammatory signals play a decisive role in the self-renewal, migration and differentiation of multipotent neural stem cells (NSCs). NSCs are believed to be able to ameliorate the symptoms of several brain pathologies through proliferation, migration into the area of the lesion and either differentiation into the appropriate cell type or secretion of anti-inflammatory cytokines. Although NSCs have beneficial roles, current evidence indicates that brain tumours, such as astrogliomas or ependymomas are also caused by tumour-initiating cells with stem-like properties. However, little is known about the cellular and molecular processes potentially generating tumours from NSCs. Most pro-inflammatory conditions are considered to activate the transcription factor NF-kappaB in various cell types. Strong inductive effects of NF-kappaB on proliferation and migration of NSCs have been described. Moreover, NF-kappaB is constitutively active in most tumour cells described so far. Chronic inflammation is also known to initiate cancer. Thus, NF-kappaB might provide a novel mechanistic link between chronic inflammation, stem cells and cancer. This review discusses the apparently ambivalent role of NF-kappaB: physiological maintenance and repair of the brain via NSCs, and a potential role in tumour initiation. Furthermore, it reveals a possible mechanism of brain tumour formation based on inflammation and NF-kappaB activity in NSCs.

Efficient animal-serum free 3D cultivation method for adult human neural crest-derived stem cell therapeutics

Due to their broad differentiation potential and their persistence into adulthood, human neural crest-derived stem cells (NCSCs) harbour great potential for autologous cellular therapies, which include the treatment of neurodegenerative diseases and replacement of complex tissues containing various cell types, as in the case of musculoskeletal injuries. The use of serum-free approaches often results in insufficient proliferation of stem cells and foetal calf serum implicates the use of xenogenic medium components. Thus, there is much need for alternative cultivation strategies. In this study we describe for the first time a novel, human blood plasma based semi-solid medium for cultivation of human NCSCs. We cultivated human neural crest-derived inferior turbinate stem cells (ITSCs) within a blood plasma matrix, where they revealed higher proliferation rates compared to a standard serum-free approach. Three-dimensionality of the matrix was investigated using helium ion microscopy. ITSCs grew within the matrix as revealed by laser scanning microscopy. Genetic stability and maintenance of stemness characteristics were assured in 3D cultivated ITSCs, as demonstrated by unchanged expression profile and the capability for self-renewal. ITSCs pre-cultivated in the 3D matrix differentiated efficiently into ectodermal and mesodermal cell types, particularly including osteogenic cell types. Furthermore, ITSCs cultivated as described here could be easily infected with lentiviruses directly in substrate for potential tracing or gene therapeutic approaches. Taken together, the use of human blood plasma as an additive for a completely defined medium points towards a personalisable and autologous cultivation of human neural crest-derived stem cells under clinical grade conditions.

Prolonged cultivation of hippocampal neural precursor cells shifts their differentiation potential and selects for aneuploid cells

Neural precursor cells (NPCs) are lineage-restricted neural stem cells with limited self-renewal, giving rise to a broad range of neural cell types such as neurons, astrocytes, and oligodendrocytes. Despite this developmental potential, the differentiation capacity of NPCs has been controversially discussed concerning the trespassing lineage boundaries, for instance resulting in hematopoietic competence. Assessing their in vitro plasticity, we isolated nestin+/Sox2+, NPCs from the adult murine hippocampus. In vitro-expanded adult NPCs were able to form neurospheres, self-renew, and differentiate into neuronal, astrocytic, and oligodendrocytic cells. Although NPCs cultivated in early passage efficiently gave rise to neuronal cells in a directed differentiation assay, extensively cultivated NPCs revealed reduced potential for ectodermal differentiation. We further observed successful differentiation of long-term cultured NPCs into osteogenic and adipogenic cell types, suggesting that NPCs underwent a fate switch during culture. NPCs cultivated for more than 12 passages were aneuploid (abnormal chromosome numbers such as 70 chromosomes). Furthermore, they showed growth factor-independent proliferation, a hallmark of tumorigenic transformation. In conclusion, our findings substantiate the lineage restriction of NPCs from adult mammalian hippocampus. Prolonged cultivation results, however, in enhanced differentiation potential, which may be attributed to transformation events leading to aneuploid cells.