Homogenization of two fluid flow in porous media

The macroscopic behavior of air and water in porous media is often approximated using Richards’ equation for the fluid saturation and pressure. This equation is parametrized by the hydraulic conductivity and water release curve. In this paper, we use homogenization to derive a general model for saturation and pressure in porous media based on an underlying periodic porous structure. Under an appropriate set of assumptions, i.e., constant gas pressure, this model is shown to reduce to the simpler form of Richards’ equation. The starting point for this derivation is the Cahn-Hilliard phase field equation coupled with Stokes equations for fluid flow. This approach allows us, for the first time, to rigorously derive the water release curve and hydraulic conductivities through a series of cell problems. The method captures the hysteresis in the water release curve and ties the macroscopic properties of the porous media to the underlying geometrical and material properties

Road-traffic pollution and asthma – using modelled exposure assessment for routine public health surveillance

Asthma is a common disease and appears to be increasing in prevalence. There is evidence linking air pollution, including that from road-traffic, with asthma. Road traffic is also on the increase. Routine surveillance of the impact of road-traffic pollution on asthma, and other diseases, would be useful in informing local and national government policy in terms of managing the environmental health risk. Several methods for exposure assessment have been used in studies examining the association between asthma and road traffic pollution. These include comparing asthma prevalence in areas designated as high and low pollution areas, using distance from main roads as a proxy for exposure to road traffic pollution, using traffic counts to estimate exposure, using vehicular miles travelled and using modelling techniques. Although there are limitations to all these methods, the modelling approach has the advantage of incorporating several variables and may be used for prospective health impact assessment. The modelling approach is already in routine use in the United Kingdom in support of the government's strategy for air quality management. Combining information from such models with routinely collected health data would form the basis of a routine public health surveillance system. Such a system would facilitate prospective health impact assessment, enabling policy decisions concerned with road-traffic to be made with knowledge of the potential implications. It would also allow systematic monitoring of the health impacts when the policy decisions and plans have been implemented

Improving the ACCRA U.S. regional cost of living index

The broadest and most commonly used measure of the cost of living across U.S. cities is the American Chamber of Commerce Research Association (ACCRA) index. This index is used by business and government organizations and the media to rank living standards and real wages across U.S. cities. In this study we reduce the aggregation bias in the index by calculating national average prices for the 59 item prices using population weights instead of the equal weight formula used by ACCRA. This correction results in a decline in the index values for all cities and changes in the rankings and bi-variate comparisons between city pairs. In some high-cost cities the index values decrease by over 25 percent, and in 74 percent of the cities the rank changes by greater than one spot.Cost and standard of living ; Wages ; Prices

Multiscale models of colloidal dispersion of particles in nematic liquid crystals

We use homogenization theory to develop a multiscale model of colloidal dispersion of particles in nematic liquid crystals under weak-anchoring conditions. We validate the model by comparing it with simulations by using the Landau–de Gennes free energy and show that the agreement is excellent. We then use the multiscale model to study the effect that particle anisotropy has on the liquid crystal: spherically symmetric particles always reduce the effective elastic constant. Asymmetric particles introduce an effective alignment field that can increase the Fredericks threshold and decrease the switch-off time

Direct Determinations of the Redshift Behavior of the Pressure, Energy Density, and Equation of State of the Dark Energy and the Acceleration of the Universe

One of the goals of current cosmological studies is the determination of the expansion and acceleration rates of the universe as functions of redshift, and the determination of the properties of the dark energy that can explain these observations. Here the expansion and acceleration rates are determined directly from the data, without the need for the specification of a theory of gravity, and without adopting an a priori parameterization of the form or redshift evolution of the dark energy. We use the latest set of distances to SN standard candles from Riess et al. (2004), supplemented by data on radio galaxy standard ruler sizes, as described by Daly and Djorgovski (2003, 2004). We find that the universe transitions from acceleration to deceleration at a redshift of about 0.4. The standard "concordance model" provides a reasonably good fit to the dimensionless expansion rate as a function of redshift, though it fits the dimensionless acceleration rate as a function of redshift less well. The expansion and acceleration rates are then combined with a theory of gravity to determine the pressure, energy density, and equation of state of the dark energy as functions of redshift. Adopting General Relativity as the correct theory of gravity, the redshift trends for the pressure, energy density, and equation of state of the dark energy out to redshifts of about one are determined, and are found to be generally consistent with the concordance model.Comment: 8 pages, 5 figures. Invited presentation at Coral Gables 200

Metamorphism and its phases

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Persistent pain after caesarean section and its association with maternal anxiety and socioeconomic background

Background: Pain, both from the surgical site, and from other sources such as musculoskeletal backache, can persist after caesarean section. In this study of a predominantly socially deprived population we have sought to prospectively examine the association between antenatal maternal anxiety and socioeconomic background and the development of persistent pain of all sources after caesarean section. Methods: Demographic details and an anxiety questionnaire were completed by 205 women before elective caesarean section. On the first postoperative day, pain scores were recorded, and at four months patients were asked to complete a Brief Pain Inventory and an Edinburgh Postnatal Depression Score. Results: Of 205 parturients recruited, 186 records were complete at the hospital admission phase and 98 (52.7%) were complete at the four-month follow-up phase. At recruitment, 15.1% reported pain. At four months 41.8% (95% CI 32.1 to 51.6%) reported pain, of whom pain was a new finding in 35.7% (95% CI 26.2 to 45.2%). Antenatal anxiety was not a significant predictor of severity of new pain at four months (P=0.43 for state anxiety, P=0.52 for trait anxiety). However, four-month pain severity did correlate with social deprivation (P=0.011), postnatal depression (P<0.001) and pain at 24 h (P=0.018). Conclusion: Persistent pain from a variety of sources after caesarean section is common. Our findings do not support the use of antenatal anxiety scoring to predict persistent pain in this setting, but suggest that persistent pain is influenced by acute pain, postnatal depression and socioeconomic deprivation

Relationship of Child Sexual Abuse Survivor Self-Perception of Consent to Current Functioning

In 1998 Rind, Tromovitch and Bauserman conducted a meta-analysis using a college sample which challenged the prevailing belief that childhood sexual abuse (CSA) has inherent deleterious effects. Resultantly, the authors proposed alternative terminology (e.g., child-adult sex), without adequate investigation into what distinguishes child-adult sex from CSA. In response, the current study investigated the relationship between CSA, consent and adult functioning in a college sample. The sample consisted of 297 undergraduate college students, ranging in age from 18 to 63-years-old. Data was collected at a mid-sized university in the southeastern United States. The measures utilized in the study include the Symptom Checklist-90 Revised (SCL 90-R), Characteristics of First Sexual Experiences and Demographics Survey, Family Adaptability and Cohesion Evaluation Scale-Second Edition (FACES-II), and the Derogatis Interview for Sexual Functioning-Revised (DISF-R). Proposed questions were, 1) prevalence of CSA in the college sample 2) the effect of CSA status and consent on the outcome measures and 3) differences in consent between the CSA and non-CSA groups. The findings were that approximately 10% of the sample reported experiencing CSA, that sexual orientation (e.g., SCL 90-R) and perceived consent of the sexual experience (e.g., SCL 90-R and FACES-II) were the only variables that significantly impacted outcomes scores, and that participants in the CSA group were significantly more likely to report being victimized in their first sexual experiences. These results suggest that based on CSA status, a college sample does not exhibit significant deficits in psychological functioning or family environment and may not be comparable to samples of CSA survivors in the general population

Laura R. Daly to Dear Sir (11 October 1962)

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