Vacancy Chains Research Articles

Evaluating Property-led Initiatives in Urban Regeneration: Tracing Vacancy Chains in Cardiff Bay

This paper contributes to the evaluation of property-led regeneration. Intervention in property markets remains an important strand in regeneration initiatives in Britain, and is still under-evaluated. In the mid 1990s, Robson and colleagues piloted a technique for helping to evaluate some of the effects of propertyled regeneration. This consisted of tracing so-called vacancy chains as the supply of new property stimulated turnover among users of buildings. Knowledge of the chains helps policy makers evaluate a particularly contentious aspect of area-based property-led initiatives: the extent to which they are stimulating new investment in a wider region, as opposed to simply moving existing employment around it. Robson's team undertook only a modest exercise in identifying chains (establishing around 40 chains in each UDC), and argued that further work was needed in order to establish the practicality of the approach and also to generate comparative data. This paper reports on a project that did this, tracing over 100 property chains in two parts of the Cardiff Bay Urban Development Area. The paper sets out, and discusses, the data acquisition techniques used, concluding that this is an approach that could have widespread application. It also reports on findings and concludes that the intervention by Cardiff Bay Development Corporation stimulated modest levels of new investment in Cardiff, but very little from beyond the sub-region.

Optical properties of vacancy related defects in diamond

Abstract〈110〉 vacancy chains, multi‐vacancy clusters and vacancy discs have been modeled using density functional theory within the AIMPRO and DFTB codes. While a connection can be established between the results on vacancy chains and previous EPR experiments, no connection can be made between the point defects and the optical properties of natural type IIa brown diamonds. However, a vacancy disc consisting of a {111} double plane of vacancies is stable and possesses an absorption spectrum similar to that found in brown diamonds. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Atomic scale engineering of nanostructures at silicon carbide surfaces

The atomic scale ordering and properties of cubic silicon carbide surfaces are investigated by room and high-temperature scanning tunneling microscopy. In this review, we will focus on the Si-terminated β-SiC(100) surfaces only. Self-formation of Si atomic lines and dimer vacancy chains on the β-SiC(100) surface is taking place at the phase transition between the 3×2 (Si-rich) and c(4×2) surface reconstructions. Using a rigorous protocol in surface preparation, it is possible to build very long, very straight and defect free Si atomic lines, forming a very large superlattice of massively parallel lines. These self-organized atomic lines are driven by stress. They have unprecedented characteristics with the highest thermal stability ever achieved for nanostructures on a surface (900°C) and the longest atomic lines ever built on a surface (micrometer scale long). Investigating their dynamics, we learn that their dismantling at high-temperature results from collective and individual mechanisms including one-by-one dimer removal. Overall, this is a model system especially suitable for nanophysics and nanotechnologies.

Forging the vacancy chain: Law enforcement efforts and mobility in criminal economies

Drawing on ethnic succession and vacancychain approaches, I argue that lawenforcement efforts targeted at establishedcriminal enterprises can lead to unintendedvacancy chains in criminal economies. Theextent and impact of these chains onmobility varies, however, depending on theextent to which amputation, decapitation,or eradication enforcement strategies areused. To illustrate this argument, Iexplore crime control policies, vacancychains and mobility in drug markets in thecities of Chicago and Osaka.

Moving patterns in the Greater Oslo region ? some evidence from a cross-section

Moving is by far the most common way to adjust housing consumption. Quantitative knowledge on the moving pattern can therefore teach us much about the typical development of housing demand, or in other words about the steps in housing careers. The paper argues that knowledge of local moving patterns can enhance our understanding of the supply of vacant housing market opportunities. As such the paper relates to the literature on Markov vacancy chain models.The paper uses a cross-section of households as a basis for empirical descriptions of moving matrixes. This type of data yields a censored sample of moves. Censoring is not random and direct estimates of the moving patterns give biased estimates. The reason is that the household sample only reports the last in a sequence of moves. The bias emerges because moves to some destinations (rented units) are more likely to be followed by a new move than moves to other destinations (typically moves into large owner-occupied units). A weighting procedure that gives unbiased estimates of the moving pattern is proposed and applied in the paper.

Job Search with Organizational Size As a Signal

It is in workers' interest to leave their jobs if better work can befound, but imperfect information on outside opportunities impedes theirjob search. We describe two theories on workers' search using the organizational size as a proxy for work characteristics and derive hypotheses on how the organizational size distribution in a labor market affects job separations. We test the hypotheses with NLSY 79 data on job separations, finding that diversity in organizational sizes affects worker mobility. Workers are more likely to move within counties with many organizations larger than their current one or many organizations of different sizes and are more likely to leave counties lacking these characteristics. Job changes alter the contents or rewards of work and are thus important for explaining stratification and social mobility. An important feature of the job change process is that many workers search for alternative jobs while holding a job, both implicitly by being willing to consider job information that reaches them through social networks and explicitly by examining want ads or sending out applications. Awareness of job market opportunities allows a worker to change jobs if a better opportunity comes along or to quickly get a new job if the current job is lost. The goal of job search is to find the best alternative possible given personal constraints such as financial difficulty, timing, location, and work environment and social constraints such as job supply, required skills, and discrimination. Sociological models of the job change process seek to model how worker goals and constraints shape the job mobility process. Models of vacancy competition (Briiderl 1992; Sorensen 1977; Tuma 1985) and vacancy chains * Financial assistance from Japan's Ministry of Education, Japan Society for the Promotion of Science is gratefully acknowledged. Two reviewers for Social Forces provided helpful

Gentrification in a Residential Mobility Framework: Social Change, Tenure Change and Chains of Moves in Stockholm

Studies of the impacts of gentrification have traditionally taken a relatively narrow view, focusing on the gentrifiers who move in and those who they displace. This paper seeks to apply the broader framework of residential mobility, using the vacancy chain concept to examine the knock-on implications across the entire housing market. Taking the case study of Stockholm, it is shown that tenure conversions from rental to co-operative ownership are of limited direct significance for gentrification. However, the indirect effects of this process, through the linked chains of household moves initiated, serve to reinforce other gentrification mechanisms operating within the rental sector, such as allocation mechanisms for rental housing. Therefore, the impacts of gentrification can be significantly underestimated if the wider effects on the housing market are ignored. It is suggested that this residential mobility approach is particularly important if the displacement effects of gentrification and the plight of any losers are to be fully appreciated.

A Single Vacancy Chain and its Bundle in Magnesium Oxide as Line-Type Lattice Defects

One-dimensional atomistic holes, i.e., a single vacancy chain and its bundle penetrating a magnesium oxide film were individually produced by convergent electron beam irradiation inside a high-resolution transmission electron microscope. The width of these imperfections ranged from 0.21 nm to 0.42 nm and was less than that of a unit cell of the NaCl structure. The imperfections were line-type lattice defects.

Vacancy clusters in plastically deformedsemiconductors

Experimental investigations of plastically deformed elemental andIII-V semiconductors prove that a high number of vacancies andvacancy clusters are formed. The formation of point defects by themotion of jogged dislocations is analysed. Vacancies formed behindthe jog are not stable as a simple chain of vacancies. Instead,they are transformed immediately to stable three-dimensionalagglomerates. The stability of various vacancy clusters has beeninvestigated by means of density-functional calculations. Thepositron lifetime in such clusters was calculated and compared toexperimental results. The association of open-volume defects withthe dislocation can be derived from positron lifetime measurements.The analysis in a positron-trapping model characterizes thedislocation as a combined defect. The undisturbed dislocation lineis a precursor trap for the positron capture in a deep trap relatedto the vacancies bound to the dislocation.

Self-organized 1D nanostructures on the β-SiC(100) surface: silicon atomic lines and dimer vacancy chains

We investigate the self-formation of Si atomic lines and dimer vacancy chains on the β-SiC(100) surface by atom resolved scanning tunneling microscopy (STM). We show that, using a rigorous protocol in surface preparation, it is possible to build very long, very straight and defect-free Si atomic lines. These lines are derived from the dimer rows of the β-SiC(100) 3×2 surface reconstruction by selective Si removal resulting, at the initial step, in very long dimer line vacancies. Using the capability of the scanning tunneling microscope to probe simultaneously both filled and empty electronic states, we confirm that these atomic lines are composed of Si–Si dimers perpendicular to the line direction. These Si atomic lines are derived from the β-SiC(100) 3×2 surface dimer rows by surface thermal dismantling including, at the initial step, Si removal “dimer row by dimer row” leaving very long dimer line vacancies. On the 3×2 surface, the Si–Si dimers are asymmetric in marked contrast with the dimers forming the Si atomic lines that are symmetric. Such a behavior is understood in terms of decreased lateral interaction between atomic lines when the spacing between them is increased. These highly stable atomic lines reveal a novel aspect of SiC in its ability to also be a very suitable material in nanotechnologies and micro/nano-electronics of the future.

Computer simulation of crystal structure formation upon transition from amorphous state

The structure of a solid has been studied by the molecular dynamics technique upon transition from the amorphous state to the crystalline state. The influence of initial conditions in the simulation of an amorphous sample and the temperature of its heating on the resulting structure is examined. It is found that structures of two types can be formed in the sample: single crystals consisting of face-centered cubic (fcc) and hexagonal close-packed (hcp) cells with a small number of pentahedral cells in the boundary region of the sample and block crystals with an ordered pentahedral structure composed of fcc, hcp, pentahedral, and icosahedral cells. Linear chains of vacancies are revealed at the boundaries of blocks.

In situHREM irradiation study of point-defect clustering in MBE-grown strainedSi1−xGex/(001)Sistructures

We present a detailed analysis of the point-defect clustering in strained ${\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}/(001)\mathrm{Si}$ structures, including the interaction of the point defects with the strained interfaces and the sample surface during 400 kV electron irradiation at room temperature. Point-defect cluster formation is very sensitive to the type and magnitude of the strain in the Si and ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ layers. A small compressive strain $(\ensuremath{-}0.3%)$ in the SiGe alloy causes an aggregation of vacancies in the form of metastable [110]-oriented chains. They are located on {113} planes and further recombine with interstitials. Tensile strain in the Si layer causes an aggregation of interstitial atoms in the forms of additional [110] rows which are inserted on {113} planes with [001]-split configurations. The chainlike configurations are characterized by a large outward lattice relaxation for interstitial rows $(0.13\ifmmode\pm\else\textpm\fi{}0.01\mathrm{nm})$ and a very small inward relaxation for vacancy chains $(0.02\ifmmode\pm\else\textpm\fi{}0.01\mathrm{nm}).$ A compressive strain higher than $\ensuremath{-}0.5%$ strongly decreases point-defect generation inside the strained SiGe alloy due to the large positive value of the formation volume of a Frenkel pair. This leads to the suppression of point-defect clustering in a strained SiGe alloy so that SiGe relaxes via a diffusion of vacancies from the Si layer, giving rise to an intermixing at the Si/SiGe interface. In material with a 0.9% misfit a strongly increased flow of vacancies from the Si layer to the SiGe layer and an increased biaxial strain in SiGe both promote the preferential aggregation of vacancies in the (001) plane, which relaxes to form intrinsic $60\ifmmode^\circ\else\textdegree\fi{}$ dislocation loops.

The transition from short-range to long-range ordering of oxygen vacancies in CaFexTi1-xO3-x/2 perovskites

The transition from isolated and finite oxygen vacancy clusters in disordered cubic perovskites to structures containing infinite chains of oxygen vacancies in an ordered arrangement was investigated by a combined Mossbauer spectroscopy, X-ray and electron diffraction and high-resolution transmission electron microscopic study. With increasing defect concentration (equivalent to an increase in the CaFeO2.5 component concentration) and/or decreasing annealing temperature, a disorder–order phase transition occurs leading to infinite chains of vacancies in the [101]cubic direction, arranged in sheets containing essentially tetrahedral iron. In the early stages of the ordering process and at low iron concentrations, these sheets exhibit orientational disorder with two different directions of vacancy chains in addition to stacking disorder with variable sequences of tetrahedral and octahedral layers. At higher vacancy concentrations, ordered layer sequences with proportions defined by stoichiometry are formed. The ordering of vacancies into infinite chains and sheets leads to a large and discontinuous decrease in ionic conductivity.

Modelling labour market dynamics with on-the-job search

A flow model of the Dutch labour market is used to calculate the effects of policy options which aim to enhance employment, especially at the lower end of the labour market. The model distinguishes between good and bad jobs, allows for endogenous wage formation and job creation, and describes the flows between these jobs so that job-to-job mobility and the vacancy chain is made endogenous. In the matching process employed job seekers with bad jobs compete with short-term and long-term unemployed for the filling of vacancies for good jobs. In each period part of the good and bad jobs are destroyed which results in inflow into unemployment. The model explicitly describes the flow of unemployed through the various duration classes of unemployment and it allows for negative duration dependence so that the escape probability from unemployment for long-term unemployed is smaller than for short-term unemployed. The model is used to simulate the effects of external shocks, such as structural productivity shocks. An impulse response analysis using the model is also conducted considering labour market policies which aims especially to enhance employment at the lower end of the labour market. In particular, the effects are analysed of measures subsidising the opening of bad jobs (jobs at the lower end of the labour market) and a rise in the productivity of a bad job as compared to a good job which can be achieved by changes in the tax system.

Beyond the Boundaries: Vacancy Chains and the Evaluation of Urban Development Corporations

Recent years have seen the establishment of numerous spatially bounded regeneration agencies in the United Kingdom, prominent amongst which have been urban development corporations (UDCs). Attempts to evaluate such agencies have so far focused almost exclusively upon the impacts within formally delimited areas and have neglected to consider the effects on surrounding nondesignated areas. In this paper, an attempt is made to address this by devising a technique for assessing the wider effects of spatially bounded regeneration agencies and programmes. Drawing from a government-commissioned evaluation of UDCs at Leeds, Bristol, and Central Manchester, we explore the extent to which government intervention in delimited areas has generated a net beneficial impact on the wider local economies of the three cities. By use of data on the nature of vacancy chains for commercial properties in the three UDCs and in their respective surrounding areas, an attempt is made to measure the degree of displacement or additionality engendered by UDC activities.

Across the border: Immigrants’ economic opportunities, social capital and informal business activities

In this article, we have explored the relationship between informal economic activities and recent immigrants in the Netherlands. First, we argue that opportunities for a significant participation of immigrants in informal economic activities have increased after 1980. On the demand side, the scope for informal economic activities has increased because of trends towards disintegration of activities in manufacturing and especially in service industries, the fragmentation of consumer markets, a gradual emergence of a demand for ‘ethnic’ products, and also owing to the dynamics of so‐called ‘vacancy chains’ whereby indigenous entrepreneurs vacate certain slots and thus create opportunities for immigrant entrepreneurs. On the supply side, processes of social exclusion and marginalisation appear to contribute to an increased participation of immigrants in informal economic activities. More or less permanent high levels of unemployment are pushing an increasing number of immigrants towards entrepreneur‐ship. They usually set up their businesses in those sectors where informal production could give them a competitive edge. Through their networks of relatives, co‐nationals or co‐ethnics they have privileged and flexible access to information, capital and ‐ with relatively low monetary costs ‐ labour. The second part of the article presents recent empirical evidence on informal economic activities on the part of immigrants. The findings confirm that immigrants are indeed heavily involved in informal methods of production in specific sectors.

Vacancy Chains and Equilibration in Senior-Level Labor Markets

In contrast to entry-level professional labor markets, in which cohorts of candidates and positions become available at the same time (e.g., when candidates graduate from school), senior level positions typically become available when an incumbent retires, or a new position is created, and when a senior position is filled a new vacancy is often created elsewhere. We model senior level labor markets as two-sided matching markets in which matchings are destabilized by retirements and new entries, and can return to stability by a decentralized process of offers and acceptances. This generalizes the standard analysis in a way which has points of contact with the sociological literature on vacancy chains.Journal of Economic LiteratureClassification Numbers: D00, C78, J63.

Female sand gobies prefer good fathers over dominant males

Female preference for males successful in male–male competition is generally assumed to result in mating with high quality males. Here I report results from an experiment disentangling the effects of intra– and intersexual selection in the sand goby, Pomatoschistus minutus , a marine fish that exhibits paternal care. I show that large males are successful in male–male competition, but contrary to what one would expect, dominants are not preferred by females and are not better at taking care of the eggs. Female preference, however, correlated with the subsequent hatching success of the eggs. Thus, female choice selects for good parenting. Hence, direct benefits in the form of superior paternal care can explain female choice in this species, supporting a good parent process of sexual selection. However, choosing on the outcome of male–male competition does not enable females to mate with the ‘best’ males.

Gross flows vs. net flows in the labor market: What is there to be learned?

Gross flows of firms, jobs and workers are very large in all phases of the business cycle, implying a great deal of heterogeneity. The order of magnitude of gross job turnover is between 16% and 23% per year, surprisingly similar across countries that differ in their institutions and net employment growth. Worker turnover is also impressive: it is found to be somewhat more variable across countries than job turnover. Relations between job flows and worker flows are established by the vacancy chain model.

The Operation of Internal Labor Markets: Staffing Practices and Vacancy Chains

The Operation of Internal Labor Markets: Staffing Practices and Vacancy Chains