Central Vacancy Research Articles

The Consequences of Rigid Wages in Search Models

The standard theory of equilibrium unemployment, the Mortensen—Pissarides search and matching model, cannot explain the magnitude of the business cycle fluctuations in two of its central elements, unemployment and vacancies. Modifying the model to make the present value of wages unresponsive to current labor market conditions amplifies fluctuations in unemployment and vacancies by an order of magnitude, significantly improving the performance of the model. Despite this, the welfare consequences of such rigid wages is negligible. (JEL: E24, E32, J30, J41, J63, J64)

A physical-based percolation model for gate oxide TDDB

Based on the physical mechanism of gate oxide TDDB, a percolation model for gate oxide degradation was brought forward, in which the occurrence and build up of deep energy-level defects, such as E′ center and oxygen vacancy were considered to be the right cause of oxide breakdown. It was pointed out that, during TDDB the stressed defects were produced in the oxide, which form local states in oxide forbidden gap. And the volume of these local states is directly proportional to the external electric field, especially when the field strength is high enough. With the by-pass of stressing time, the concentration of defects in the oxide grew continually. As an effect, the distance between neighboring local states become shorter. So, hopping or tunneling probabilities of electrons between these local states increase swiftly. As a result, a conduction path will form when the distance between neighboring local states reaches a critical value. At the same time, in terms of energy band theory, an extended energy level will form in the oxide forbidden gap. Accompanied by a rapid increase of SILC, the gate oxide undergoes breakdown.

An Empirical Analysis of Community Center Rents

This article is the winner of the Retail Real Estate manuscript prize (sponsored by the International Council of Shopping Centers) presented at the 2001 American Real Estate Society Annual Meeting.This study empirically models the determinants of community center rent. It employs a two-stage model that estimates center vacancy in the first stage and then includes predicted vacancy in a second stage demand model investigating endogenous and exogenous determinants of community center rent. The data includes information on maximum and minimum square foot rent for 118 community centers in Atlanta, Georgia. Maximum community center rent is highly correlated with a center's predicted vacancy rate and location within the Atlanta area. Additionally, rent at both maximum and minimum levels is influenced by trade area purchasing power, property age and to a lesser extent by proximity to a regional mall, center design and neighborhood factors.

Micro-Market Determinants of Neighborhood Center Rental Rates

This investigation expands the limited empirical research on retail rental rates by investigating the determinants of neighborhood shopping center rents. Evidence supports primary trade area and property specific characteristics as the primary determinants of neighborhood center vacancy and rental rates. A positive aggregation effect created by higher order shopping opportunities is also found. Community centers and malls generate positive marginal effects on neighborhood center rental rates. However, the marginal effects diminish greatly after two-tenths mile for community centers and one-half mile for malls. Micro-market factors are important determinants of rental rates and by implication property performance.

Collective diffusion on strongly correlated heterogeneous surfaces

Collective diffusion coefficients are studied for heterogeneous bivariate surfaces with two different topographies, namely the random patches and the chessboard-like ordered distributions. The topography is shown to affect strongly the coverage dependence of the transport coefficients. Various diffusion quantities like the chemical D, jump D J and tracer D∗ diffusion coefficients are analyzed by means of Monte Carlo simulations in the framework of the fluctuation and the Kubo–Green theory. The behavior of diffusion coefficients in small patches is mainly affected by the mobility of the particles in the border vacancies, and a simple law is obtained for the ratio D(1)/ D(0). For large patches the behavior is dominated by the mobility of particles in the central vacancies. In the limit of very large patches the diffusion coefficients become independent of the energetic topography.

New magic numbers in metallic clusters: an unexpected metal dependence

Using a many-body tight-binding potential within the second moment approximation in a quenched molecular dynamics simulation, we calculate the internal energy of free Cu, Ag and Au clusters of various sizes and morphologies. We find that the icosahedral structure, which is the equilibrium shape for small sizes at least for Cu and Ag, adopts a very inhomogeneous atomic relaxation. More surprisingly, introducing a vacancy at the center lowers the mean energy per atom for sufficiently large size icosahedra. This means that above a critical size, which decreases from Cu to Au, the icosahedron admits a constitutional vacancy. Taking into account the stability domain of the icosahedron relative to the fcc structure (namely the Wulff polyhedron), we find that there is a stability range of size for Cu and Ag icosahedra with a central vacancy, but not for Au icosahedra. This trend along the noble metal column is discussed in view of tight-binding potential parameters.

Correlation of the cationic ‘charge of transport’ with the nonstoichiometry and the oxygen exponents in C1−δO

An attempt has first been made to correlate the cationic charge of transport ( α 1 ∗ ) with the nonstoichiometry (δ) as well as with the reciprocal oxygen exponents of the conductivity and the nonstoichiometry for the system C 1− δ O . The cationic charge of transport tends to increase monotonically, but at a lesser and lesser rate, with δ at a given temperature and appears to be linearly correlated with reciprocal oxygen exponents. These correlations suggest that the charge of transport may be viewed as a measure of the relaxation effect between the surrounding electronic charge cloud and the central cation vacancy (V Co ″ )or as the number of holes associated with the vacancy in an average sense which reduces the effective charge of the vacancy.

Dynamic behaviour of a small atomic cluster on an Ir(001) surface

Abstract The dynamic behaviour of small atomic clusters consisting of eight atoms and ten atoms on an Ir(001) surface has been studied using a field ion microscope. It has been found that eight-atom and ten-atom clusters are energetically favoured to form ring configurations with central lattice vacancies in the clusters. The fact that the atomic-ring configurations with fewer nearest-neighbour bonds are more thermally stable than those dense cluster structures with more nearest-neighbour bonds demonstrates convincingly the general believed non-additivity of bond energies at the metal surface.

Deep levels in γ-ray irradiated n- and p-type hydrogen-grown float-zoned silicon

The generation rates and annealing behavior of the irradiation defects in n- and p-type hydrogen-grown float-zoned silicon (irradiated with γ rays from 60Co) have been studied by the deep-level transient spectroscopy technique and compared with those of irradiated argon-grown float-zoned silicon. Assuming the generation rate of the irradiation defects created by γ rays in argon-grown float-zoned silicon is 1, then the generation rates of the A center, divacancy, and phosphorus vacancy in n-type hydrogen-grown float-zoned silicon are 0.23, 0.78, and 0.19, respectively, while the generation rates of the divacancy and H(0.37 eV) in p-type hydrogen-grown silicon are 0.79 and 0.10, respectively. Due to the existence of hydrogen, the generation rate reduction of the major irradiation defects in γ-ray irradiated silicon is more pronounced than that in 1-MeV electron irradiated silicon. Three hydrogen-related defects, H(0.10 eV), H(0.29 eV), and H(0.56 eV), were seen in γ-ray irradiated hydrogen-grown float-zoned silicon, among which H(0.10 eV) and H(0.56 eV) were reported by us to exist in electron irradiated hydrogen-grown float-zoned silicon, while H(0.29 eV) is reported for the first time. The convergence effect of annealing temperatures for the irradiation defects was observed. That is, the annealing temperatures at which the irradiation defects diminish are almost the same for most irradiation defects, similar to that in the case of electron irradiation, was observed, showing that this effect is characteristic of the hydrogen behavior in silicon, and irrelevent to the type of irradiation.

Immersion of hydrogen atoms in aluminium clusters

The immersion of a H atom at the centre of AlN clusters with 8≦N≦21 has been studied using the density functional formalism and a pseudopotential averaged about the cluster centre. The immersion energy is negative forN≦12, due to the fact that the corresponding pure Al clusters contain a central vacancy, which shows a strong affinity for the H atom. For larger sizes the immersion energy is positive (with a few exceptions), since the H atom must displace a central Al atom to the cluster surface, and it shows non negligible size oscillations.

Pre-melting effects in lead from resistance measurements

The resistance of a lead sample was measured with very high accuracy from 295K to the melting temperature 600.7K. Up to about 540K the resistance is determined by electron-phonon and electron-vacancy scattering with a vacancy formation enthalpy of 0.38 eV. Above 540K there is an additional term in the resistance, well described by a thermally created defect with a formation enthalpy of 1.42 eV. While the vacancy formation entropy is approximately 1.6kB the formation entropy of the new defect is approximately 16kB. This leads the authors to believe that the new defect has a liquid-like structure and consists approximately of a central atom or vacancy plus its nearest neighbours.

Where, when, and how male sharp-tailed grouse establish territories on arenas

The behaviour of individually marked male sharp-tailed grouse (Pedioecetes phasianellus) was observed on four arenas over two successive autumn-to-spring periods to determine the fate of established birds, and where, when, and how young males established new territories on the arenas. The lekking cohort of males frequented the arenas from September to June with peak attendance in April. This cohort suffered an average loss of 56% between spring and autumn with males occupying peripheral territories disappearing in greater proportions than those on central territories; this loss is believed to represent mortality. Surviving males moved centripetally to fill any central vacancies, leaving potential territories vacant peripherally. It was only here at the edge of the arena that young males were recorded successfully establishing territories. Most (68%) were established in autumn and early winter. Males in adult plumage (assumed to be about 18 months old) were relatively more successful (13/15) in acquiring territories between September and March than birds in immature plumage (about 6 months old) (11/23). Acquisition of a territory appeared to involve the following sequence of events: repeated use of a site, low intensity display (mainly towards more peripherally located and largely nonterritorial males), establishment of mutual recognition, full display, and defence of space against all neighbours.

Spacial organization among male sharp-tailed grouse on arenas

Spacial organization among lekking sharp-tailed grouse was investigated, in the spring of 1969, near Wainwright, Alberta, by sequentially removing territorial males from the centers of two arenas and recording the responses shown by remaining territory holders. Vacancies created on each arena were filled by an adjacent male or shared by two or three birds in contiguous territories. Central vacancies were filled in an orderly and predictable manner: first by males in a central group of territories, then by males in territories surrounding die central group, and finally by peripheral males. As the number of males on arenas was reduced, the area occupied by the system of territories also shrank. Thus, territory size remained constant as did density of males on the arena. The means by which the spacial configuration of territories was attained and maintained are discussed.

The effects of pre-irradiation treatments on the chemical behavior of 115Cd recoil atoms in neutron irradiated cadmium phthalocyanine

The chemical behavior of 115Cd recoil atoms was studied in cadmium phthalocyanine which had been subjected to pre-irradiation treatments such as quenching, irradiation with γ-rays, or irradiation in a nuclear reactor. It was found that the initial retention of the quenched sample was smaller than that of the untreated sample, and that the difference between the initial and the plateau retention, ΔR, increased when the sample had been quenched from 190°C. Only a small change in the behavior of the recoil atoms was observed in both cases of irradiation prior to the recoil reaction. The results are discussed in terms of the defects; the central metal vacancies introduced in the complex by quenching has a big effect on the subsequent course of the thermal annealing reaction.

Electron Capture byαandFCenters in KBr

Photoconductivity measurements were made on KBr containing $\ensuremath{\alpha}$, $F$, and ${F}^{\ensuremath{'}}$ centers to determine the electron-trapping probability (probability per unit time that one defect per ${\mathrm{cm}}^{3}$ traps an electron) of the $F$ center and the $\ensuremath{\alpha}$ center or negative-ion vacancy. The electron-trapping probability of the $\ensuremath{\alpha}$ center increased from 3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ ${\mathrm{cm}}^{3}$ per sec at 118\ifmmode^\circ\else\textdegree\fi{}K to 6\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{3}$ per sec at 24\ifmmode^\circ\else\textdegree\fi{}K. The electron-trapping probability of the $F$ center increased from 3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ ${\mathrm{cm}}^{3}$ per sec at 118\ifmmode^\circ\else\textdegree\fi{}K to 4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ ${\mathrm{cm}}^{3}$ per sec at 24\ifmmode^\circ\else\textdegree\fi{}K. The initial capture of an electron by an $\ensuremath{\alpha}$ center results in the formation of an excited $F$ center. The binding energy of this excited state was found to be 0.130 eV, corresponding to the first excited state of the $F$ center. Electron capture by an $F$ center was interpreted as occurring through the formation of an excited ${F}^{\ensuremath{'}}$ center. The binding energy of this state was found to be between 0.04 and 0.08 eV.