Multiple Occupancy Research Articles

Varieties of things: foundations of contemporary metaphysics

Preface. PART I: METAPHYSICS AND ITS TOOLS . 1: The Nature and Function of Metaphysics. The Methodology and Subject Matter of Metaphysics. Aristotle's Conception of Metaphysics. Kant's Conception of Metaphysics. A Working Conception of Metaphysics. 2: Some Tools of Metaphysics. Criteria of Ontological Commitment: Two Examples. 'No Entity Without Identity': Identity Conditions for Objects. Individuation Conditions, Identity Conditions, and Metaphysical Kinds. Principles and Criteria of Identity. PART II: PARTICULARS. 3: Material Substances. Our Ontological Commitment to Material Substances. The Bundle Theory and the Principle of the Identity of Indiscernibles. Problems with the Bundle Theory. The Bare Substratum Theory and The Principle of Acquaintance. Objections to the Bare Substratum Theory. An Alternative. 4: Persons and Personal Identity. Our Ontological Commitment to Persons. Candidates for Persistence Conditions for Persons. The Closest Continuer Theory. Does the Concept of Identity Apply to Persons?. The Multiple Occupancy Thesis. Back to Basics: Continuity and Fission. A Suggestion. 5: Events. Our Ontological Commitment to Events. Three Criteria: Spatio-temporal Coincidence, Necessary Spatio-temporal Coincidence, and Sameness of Cause and. Effect. The Property Exemplification Account of Events. PART III: UNIVERSALS. 6: Universals and the Realism/Nominalism Dispute. The Issue. Varieties of Nominalism. Two Conceptions of Universals. The Regress Charge and Two Unsuccessful Attempts to Meet It. An Alternative. Notes. Bibliography. Index

Income, Housing, and Fire Injuries: A Census Tract Analysis

This study investigates the social and demographic correlates of nonfatal structural fire injury rates for the civilian population for Philadelphia census tracts during 1993-2001. The author analyzed 1,563 fire injuries by census tract using the 1990 census (STF 3) and unpublished data from the Office of the Fire Marshal of the Philadelphia Fire Department. Injury rates were calculated per 1,000 residents of a given census tract. Multiple regression was used to determine significant variables in predicting fire injuries in a given census tract over a nine-year period and interaction effects between two of these variables-age of housing and income. Multiple regression analysis indicates that older housing (prior to 1940), low income, the prevalence of vacant houses, and the ability to speak English have significant independent effects on fire injury rates in Philadelphia. In addition, the results show a significant interaction between older housing and low income. Given the finding of very high rates of fire injuries in census tracts that are both low income and have older housing, fire prevention units can take preventative measures. Fire protection devices, especially smoke alarms, should be distributed in the neighborhoods most at risk. Multiple occupancy dwellings should have sprinkler systems and fire extinguishers. Laws concerning the maintenance of older rental housing need to be strictly enforced. Vacant houses should be effectively boarded up or renovated for residential use. Fire prevention material should be distributed in a number of languages to meet local needs.

Microscopic model of clathrate compounds

The major generalization of the existing theory of clathrate hydrates, so that it can account for phenomena such as multiple occupancy of individual cages and mutual guest-host couplings and guest-guest interaction, are suggested. The new model allows taking into account the influence of guest molecules on the host lattice. Atomistic modeling of structural, dynamical and thermodynamic properties of ices and different hydrates at high pressures and a range of temperature were performed. The influence of guest molecules (argon, methane and xenon) on the host lattice of hydrate of cubic structures I and II was investigated. Results of these calculations agree with known experimental data.

NMR shielding constants for hydrogen guest molecules in structure II clathrates

Proton NMR shielding constants and chemical shifts for hydrogen guests in small and large cages of structure II clathrates are calculated using density-functional theory and the gauge-invariant atomic-orbital method. Shielding constants are calculated at the B3LYP level with the 6-311++G(d,p) basis set. The calculated chemical shifts are corrected with a linear regression to reproduce the experimental chemical shifts of a set of standard molecules. The calculated chemical shifts of single hydrogen molecules in the small and large structure II cages are 4.94 and 4.84 ppm, respectively, which show that within the error range of the method the H2 guest molecules in the small and large cages cannot be distinguished. Chemical shifts are also calculated for double occupancy of the hydrogen guests in small cages, and double, triple, and quadruple occupancy in large cages. Multiple occupancy changes the chemical shift of the hydrogen guests by approximately 0.2 ppm. The relative effects of other guest molecules and the cage on the chemical shift are studied for the cages with multiple occupancies.

The health consequences of multiple roles at older ages in the UK

Increasing proportions of men and women are combining family (including care-giving) and work responsibilities in later life; however, the relationship between multiple role commitments and health at older ages remains unclear. Employing data from the longitudinal Retirement Survey (1988-1989 and 1994), the present authors applied logistic regression models to investigate the relationship between multiple role occupancy (1) cross-sectionally in 1988-1989 and health status in 1994; (2) retrospectively over the respondent's lifetime up to 1988-1989 and health outcomes in 1988-1989; and (3) retrospectively between 1988-1989 and 1994, and health status in 1994. The health outcomes considered were (1) general health status, (2) functional ability and (3) severity of disability category. Overall, simultaneous role occupancy (e.g. care-giving and employment) at older ages does not appear to be associated with poor health. The authors report a positive association between employment and health, as expected. There were mixed results concerning the association between care-giving and health. Where adverse health outcomes were found, the parental role, alone or in combination with other roles, was most frequently related to poor health. Thus, for a nationally representative sample of mid-life men and women, the combination of care-giving with other family and work roles appears to have few negative health consequences. Further research is needed on whether continued parental demands in mid-life have a negative impact on health.

Barrier-less knock-on conduction in ion channels: peculiarity or general mechanism?

Abstract A mechanism of barrier-less knock-on conduction is postulated for the best-studied KcsA ion channel. The conduction proceeds as follows: an ion enters the channel, which already contains two ions and “push” them along the pore. As a result, the state of triple occupancy forms. Eventually, the ion from the opposite side escapes to solution and the state of double occupancy is restored. The energies of the states with double and triple occupancies are almost the same, which makes alternation of these states possible. However, it is not known whether this mechanism is universal or specific for a narrow class of KcsA-like channels, which can accommodate just two or three ions in the selectivity filter. In the present work we develop a simplified model of the ion channel selectivity filter, which allows us to study the conduction in a broad range of ion occupancies using the Brownian dynamics. We show that knock-on barrier-less conduction occurs when the energies of adjacent equilibrium occupancy states are the same, regardless of the exact number of ions accommodated in the channel. It is shown that the maximal possible current flows through the channel in the regime of knock-on conduction. This allows us to conclude that knock-on barrier-less conduction can be considered as a universal mechanism of ions’ translocation in the ion channels with multiple occupancy.

On the thermodynamic stability of clathrate hydrates IV: double occupancy of cages.

We have extended the van der Waals and Platteeuw theory to treat multiple occupancy of a single cage of clathrate hydrates, which has not been taken into account in the original theory but has been experimentally confirmed as a real entity. We propose a simple way to calculate the free energy of multiple cage occupancy and apply it to argon clathrate structure II in which a larger cage can be occupied by two argon atoms. The chemical potential of argon is calculated treating it as an imperfect gas, which is crucial to predict accurate pressure dependence of double occupancy expected at high pressure. It is found that double occupancy dominates over single occupancy when the guest pressure in equilibrium with the clathrate hydrate exceeds 270 MPa.

Family, work and quality of life: changing economic and social roles through the lifecourse

This article reports research funded as part of the recent ESRC Growing Older initiative. The project ‘Family, Work and Quality of Life’ explored changes in economic and social roles across four birth cohorts passing through mid-life (45–59/64 years) in Britain. The relationship between multiple role responsibilities and a range of indicators of quality of life, including material resources, health and engagement in social activities were investigated. The research was based upon secondary analysis of four different surveys: the 2000 British Household Panel Study, the 1994–95 Family and Working Lives Survey, the 1985, 1990, 1995, and 2000 General Household Surveys, and the longitudinal Retirement Survey (1988/89 and 1994). A particularly interesting finding is that being ‘caught in the middle’, in terms of having simultaneous care-giving responsibilities to dependent children and frail parents whilst in paid work, has been atypical. Only one-in-nine British women, and one-in-ten British men, aged 45–49 years (born in 1941–45) occupy all three roles concurrently, but multiple role occupancy is increasing across cohorts, particularly the combination of caring and paid work. Role occupancy significantly affects the accumulation of pension entitlements (particularly second-tier pensions), with the effect that many women who have fulfilled the important social roles of carer and parent will face a low income in old age. Where adverse health outcomes were found, parental role in mid-life was most frequently associated with such poor health, suggesting that continued parental demands in mid-life may have negative health consequences.

Scaling of Star Polymers with 1−80 Arms

We present large statistics simulations of 3-dimensional star polymers with up to $f=80$ arms, and with up to 4000 monomers per arm for small values of $f$. They were done for the Domb-Joyce model on the simple cubic lattice. This is a model with soft core exclusion which allows multiple occupancy of sites but punishes each same-site pair of monomers with a Boltzmann factor $v<1$. We use this to allow all arms to be attached at the central site, and we use the `magic' value $v=0.6$ to minimize corrections to scaling. The simulations are made with a very efficient chain growth algorithm with resampling, PERM, modified to allow simultaneous growth of all arms. This allows us to measure not only the swelling (as observed from the center-to-end distances), but also the partition sum. The latter gives very precise estimates of the critical exponents $\gamma_f$. For completeness we made also extensive simulations of linear (unbranched) polymers which give the best estimates for the exponent $\gamma$.

A probabilistic model for the equilibration of an ideal gas

I present a generalization of the Ehrenfest urn model that is aimed at simulating the approach to equilibrium in a dilute gas. The present model differs from the original one in two respects: (1) the two boxes have different volumes and are divided into identical cells with either multiple or single occupancy; (2) particles, which carry also a velocity vector, are subjected to random, but elastic, collisions, both mutual and against the container walls. I show, both analytically and numerically, that the number and energy of particles in a given urn evolve eventually to an equilibrium probability density W which, depending on cell occupancy, is binomial or hypergeometric in the particle number and beta-like in the energy. Moreover, the Boltzmann entropy ln W takes precisely the same form as the thermodynamic entropy of an ideal gas. This exercise can be useful for pedagogical purposes in that it provides, although in an extremely simplified case, a probabilistic justification for the maximum-entropy principle.

Theoretical Study of Clathrate Hydrates with Multiple Occupation

In this work, the electronic, structural, dynamic andthermodynamic properties of structure II, H and tetragonalAr clathrate hydrates have been calculated and the effectof multiple occupancy on their stability has been examinedusing first-principles and lattice dynamics calculations.The dynamic properties of these clathrates have beeninvestigated depending on the number of guest moleculesin a clathrate cage. It has been found that selectedhydrate structures are dynamically stable. The calculatedcell parameters are in agreement with experimental data.We also report the results of a systematic investigationof cage-like water structures using first-principles calculations. Ithas been observed that Ar clusters can be stabilized indifferent water cages and the stability is strongly dependenton the number of argon atoms inside the cages.

Phase separation of a multiple occupancy lattice gas

A binary lattice gas model that allows for multiple occupancy of lattice sites, inspired by recent coarse-grained descriptions of solutions of interacting polymers, is investigated by combining the steepest descent approximation with an exploration of the multidimensional energy landscape, and by Gibbs ensemble Monte Carlo simulations. The one-component version of the model, involving on site and nearest neighbour interactions, is shown to exhibit microphase separation into two sub-lattices with different mean occupation numbers. The symmetric two-component version of the multiple occupancy lattice gas is shown to exhibit a demixing transition into two phases above a critical mean occupation number.

Quasi-particles in the selectivity filter can explain permeation in a channel with multiple occupancy

It is established that the permeation in the selectivity filter of KcsA-like channels occurs in a “knock-on” manner and involves concerted motion of multiple ions. We present a theoretical approach, which explains this intriguing process, built up from basic physical principles. The predictions of the theory are systematically compared to explicit Brownian dynamics simulations and experimental data for the KcsA channel. We show that the motion of the ions in the selectivity filter can be reduced to the motion of a single quasi-particle called a quasi-ion. The quasi-ions perform the actual charge transfer in the filter. The concept of quasi-ions provides an elegant explanation of barrier-less “knock-on” conduction in the selectivity filter and allows us to avoid explicit description of the motion of individual ions in the multi-ion channel. The later can help to bridge the gap between detailed molecular and Brownian dynamics simulations and the macroscopic properties of the channels.

Ab Initio Study of Hydrogen Storage in Hydrogen Hydrate Clathrates

Recently, for the first time a hydrate clathrate was discovered with hydrogen. Aside from the great technological promise that is inherent in storing hydrogen at high density at modest pressures, there is great scientificinterest as this would constitute the first hydrate clathrate with multiple species per cage. The multiple cage occupancy is controversial, and reproducibility of the experiments has been questioned. Therefore, in this study we try to illucidate the stability of the hydrogen hydrate clathrate, and determine the thermodynamically most favored cage occupancy using highly accurate ab initio computer simulations.

Thermodynamic stability of hydrogen clathrates.

The stability of the recently characterized type II hydrogen clathrate [Mao, W. L., Mao, H.-K., Goncharov, A. F., Struzhkin, V. V., Guo, Q., et al. (2002) Science 297, 2247-2249] with respect to hydrogen occupancy is examined with a statistical mechanical model in conjunction with first-principles quantum chemistry calculations. It is found that the stability of the clathrate is mainly caused by dispersive interactions between H2 molecules and the water forming the cage walls. Theoretical analysis shows that both individual hydrogen molecules and nH2 guest clusters undergo essentially free rotations inside the clathrate cages. Calculations at the experimental conditions--2,000 bar (1 bar = 100 kPa) and 250 K confirm multiple occupancy of the clathrate cages with average occupations of 2.00 and 3.96 H2 molecules per D-5(12) (small) and H-5(12)6(4) (large) cage, respectively. The H2-H2O interactions also are responsible for the experimentally observed softening of the H[bond]H stretching modes. The clathrate is found to be thermodynamically stable at 25 bar and 150 K.

Multiple magnetic transitions in single-crystalGd5Rh4Ge10

Compounds belonging to the ${R}_{5}{\mathrm{Ir}}_{4}{\mathrm{Si}}_{10}$ family exhibit a variety of ground states depending on the nature of the rare-earth element R. In this work, we report resistivity, magnetization, and heat-capacity studies on a single crystal of ${\mathrm{Gd}}_{5}{\mathrm{Rh}}_{4}{\mathrm{Ge}}_{10}.$ Unusual multiple magnetic transitions are observed in ${\mathrm{Gd}}_{5}{\mathrm{Rh}}_{4}{\mathrm{Ge}}_{10}$ (where there is no crystal-field contribution). It appears that one of the four-fold transitions which occurs at the highest temperature is a second-order (continuous) phase transition while the other three probably involving moment reorientations and noncollinear amplitude modulations. In general, the basic cause of the magnetic orderings is due to anisotropic indirect exchange interaction (Ruderman-Kittel-Kasuya-Yasida type) coupled with multiple site occupancy of the Gd atoms.

A method for determining two substrates binding in the same active site of cytochrome P450 BM3: an explanation of high energy ω product formation

A number of enzymes from the cytochrome P450 family show atypical (non-Michaelis–Menten) kinetic behavior resulting from substrate activation, inhibition, partial inhibition, biphasic saturation, or autoactivation. Herein, we provide a technique that can identify multiple substrate occupancy in the same active site of a P450 as a result of an altered kinetic profile. Using an isotope effect on product ratios confirms that the enzyme–substrate (ES) complex responsible for ω hydroxylation of palmitic acid (palmitate) is in rapid equilibrium with the ES complex that leads to ω-1 hydroxylation of palmitate. Co-incubation of a second substrate, lauric acid (laurate), results in a change in the ratio of ω to ω-1 hydroxylated palmitate. Furthermore, an isotope effect on palmitate is observed when deuterated laurate is co-incubated with non-deuterated palmitate. These results are only consistent with both substrates being in the same active site simultaneously. This mode of binding explains how the F87A mutant of P450 BM3 is able to produce the ω alcohol, a product that arises from the high-energy primary radical.

Lattice model for the kinetics of rupture of fluid bilayer membranes.

We have constructed a model for the kinetics of rupture of membranes under tension, applying physical principles relevant to lipid bilayers held together by hydrophobic interactions. The membrane is characterized by the bulk compressibility (for expansion) K, the thickness 2h(t) of the hydrophobic part of the bilayer, the hydrophobicity sigma, and a parameter gamma characterizing the tail rigidity of the lipids. The model is a lattice model which incorporates strain relaxation, and considers the nucleation of pores at constant area, constant temperature, and constant particle number. The particle number is conserved by allowing multiple occupancy of the sites. An equilibrium "phase diagram" is constructed as a function of temperature and strain with the total pore surface and distribution as the order parameters. A first-order rupture line is found with increasing tension, and a continuous increase in protopore concentration with rising temperature till instability. The model explains current results on saturated and unsaturated phosphatidylcholine lipid bilayers and thicker artificial bilayers made of diblock copolymers. Pore size distributions are presented for various values of area expansion and temperature, and the fractal dimension of the pore edge is evaluated.

A Complex Fulleride SuperstructureDecoupling Cation Vacancy and Anion Orientational Ordering in Ca3+xC60 with Maximum Entropy Data Analysis

The structure of the alkaline-earth fulleride Ca 3.01 C 60 is refined using maximum entropy data analysis of synchrotron powder diffraction data. Despite the size and complexity of the structural problem, the fulleride anion orientations and the details of multiple occupancy of the octahedral interstitial sites in the fcc anion array are determined. The power of the maximum entropy technique in solving underdetermined problems in powder crystallography is thus demonstrated.

Multiple Role Occupancy in Midlife: Balancing Work and Family Life in Britain

This article investigates the extent of multiple-role occupancy among midlife individuals in Britain in cross-section and over the life course, focusing on work and family commitments. The association between demographic and social factors and multiple-role obligations is also investigated. The research is based on secondary analysis of the British Family and Working Lives Survey, which contains retrospective paid work, caregiving, and child coresidence histories. The proportion of individuals in midlife (women aged 45-59 and men aged 45-64) who have multiple roles, in terms of paid work and consistent family care, at any one point in time is low (2%). This is primarily due to the relatively small proportion (7%) of people in this age group who are caring for a dependent. Being older, unmarried, and in poor health significantly reduces the number of roles held among men and women. Although the frequency of multiple role occupancy, and intensive multiple role occupancy, is low on a cross-sectional basis, a much higher proportion of individuals have ever occupied multiple roles over their life course (14%). The findings will inform debate on how policy can best aid those endeavouring to balance paid work, family life, and caring responsibilities.