Fluid Flows of Mixed Regimes in Porous Media

In porous media, there are three known regimes of fluid flows, namely, pre-Darcy, Darcy and post-Darcy. Because of their different natures, these are usually treated separately in literature. To study complex flows when all three regimes may be present in different portions of a same domain, we use a single equation of motion to unify them. Several scenarios and models are then considered for slightly compressible fluids. A nonlinear parabolic equation for the pressure is derived, which is degenerate when the pressure gradient is either small or large. We estimate the pressure and its gradient for all time in terms of initial and boundary data. We also obtain their particular bounds for large time which depend on the asymptotic behavior of the boundary data but not on the initial one. Moreover, the continuous dependence of the solutions on initial and boundary data, and the structural stability for the equation are established.Comment: 33 page

On modeling and measuring viscoelasticity with dynamic Atomic Force Microscopy

The interaction between a rapidly oscillating atomic force microscope tip and a soft material surface is described using both elastic and viscous forces with a moving surface model. We derive the simplest form of this model, motivating it as a way to capture the impact dynamics of the tip and sample with an interaction consisting of two components: interfacial or surface force, and bulk or volumetric force. Analytic solutions to the piece-wise linear model identify characteristic time constants, providing a physical explanation of the hysteresis observed in the measured dynamic force quadrature curves. Numerical simulation is used to fit the model to experimental data and excellent agreement is found with a variety of different samples. The model parameters form a dimensionless impact-rheology factor, giving a quantitative physical number to characterize a viscoelastic surface that does not depend on the tip shape or cantilever frequency.Comment: 13 pages, 7 figure

Pore-scale numerical investigation of pressure drop behaviour across open-cell metal foams

The development and validation of a grid-based pore-scale numerical modelling methodology applied to five different commercial metal foam samples is described. The 3-D digital representation of the foam geometry was obtained by the use of X-ray microcomputer tomography scans, and macroscopic properties such as porosity, specific surface and pore size distribution are directly calculated from tomographic data. Pressure drop measurements were performed on all the samples under a wide range of flow velocities, with focus on the turbulent flow regime. Airflow pore-scale simulations were carried out solving the continuity and Navier–Stokes equations using a commercial finite volume code. The feasibility of using Reynolds-averaged Navier–Stokes models to account for the turbulence within the pore space was evaluated. Macroscopic transport quantities are calculated from the pore-scale simulations by averaging. Permeability and Forchheimer coefficient values are obtained from the pressure gradient data for both experiments and simulations and used for validation. Results have shown that viscous losses are practically negligible under the conditions investigated and pressure losses are dominated by inertial effects. Simulations performed on samples with varying thickness in the flow direction showed the pressure gradient to be affected by the sample thickness. However, as the thickness increased, the pressure gradient tended towards an asymptotic value

Rasch Analysis of the International Quality of Life Basic Data Set Version 2.0

Objective: To examine the internal construct validity of the International Spinal Cord Injury Quality of Life Basic Data Set Version 2.0 (QoL-BDS V2.0) and compare this with the internal construct validity of the original version of the QoL-BDS. Design: International cross-sectional psychometric study. Setting: Spinal rehabilitation units, clinics, and community. Participants: The study involved 5 sites and 4 countries, 2 of whose primary language is not English. Each site included a consecutive sample of inpatients with spinal cord injury or disease (SCI/D) and a convenience sample of individuals with SCI/D living in the community (N=565). Main outcome measures: The QoL-BDS V2.0 consists of the 3 original items on satisfaction with life as a whole, physical health, psychological health of the QoL-BDS, and an additional item on satisfaction with social life. All 4 items are answered on a 0-10 numeric rating scale. Rasch analysis was performed on versions 1.0 and 2.0 of the QoL-BDS to examine the ordering of the items' response options, item scaling, reliability, item fit, local item independence, differential item functioning, and unidimensionality. Results: The sample included 565 participants with 57% outpatients and 43% inpatients. Mean age was 51.4 years; 71% were male; 65% had a traumatic injury, 40% had tetraplegia, and 67% were wheelchair users. Item thresholds were collapsed for ordering, and subsequent analyses showed good internal construct validity for the QoL-BDS V2.0 with a person separation reliability of 0.76 and Cronbach α of 0.81. Infit and outfit statistics ranged 0.62-0.91. No local dependencies and multidimensionality were found. Differential item functioning was observed only for country and inpatients vs outpatients but not for other participants' characteristics. Differences in internal construct validity between the 3-item and 4-item versions were minimal. Conclusions: The results of this Rasch analysis support the internal construct validity of the QoL-BDS V2.0

Modeling and Measuring Viscoelasticity with Dynamic Atomic Force Microscopy

The interaction between a rapidly oscillating atomic-force-microscope tip and a soft-material surface is described with use of both elastic and viscous forces in a moving-surface model. We present the simplest form of this model, motivating our derivation with the models ability to capture the impact dynamics of the tip and sample with an interaction consisting of two components: interfacial or surface force, and bulk or volumetric force. Analytic solutions to the piecewise linear model identify characteristic time constants, providing a physical explanation for the hysteresis observed in the measured dynamic-force-quadrature curves. Numerical simulation is used to fit the model to experimental data, and excellent agreement is found with a variety of different samples. The model parameters form a dimensionless impact-rheology factor, giving a quantitative physical number to characterize a viscoelastic surface that does not depend on the tip shape or cantilever frequency

The social dimension of quality of life following spinal cord injury or disease:an international ICF-linking study

Study design: International Classification of Functioning, Disability and Health (ICF) linking study. Objective: Analyze cognitive interview data using the ICF as an analytic framework, to examine aspects of social life relevant to quality of life (QoL) according to people with spinal cord injury or disease (SCI/D). This study builds upon results of an international study about the cross-cultural validity of the International SCI QoL Basic Data Set (QoL-BDS). Setting: Four specialized outpatient clinics in SCI/D rehabilitation, from the US, Brazil and Australia. Methods: Analysis of qualitative data from 39 cognitive interviews with SCI/D patients at least one year post onset. Participants were asked to define their concept of QoL, overall life satisfaction, physical health and psychological health, and other relevant matters. Four independent researchers coded text fragments related to the items, and fragments were linked to ICF chapters d6–d9, following established linking rules. Results: The proportion of text referring to social life was 35.8% (definition QoL), 24.9% (QoL life as whole), 6.0% (physical health) and 34.9% (psychological health). The most frequent ICF categories were d760 Family relationships, d770 Intimate relationships and d920 Recreation and leisure. Most frequent responded social topics to the ‘other issues’ item were d770 Intimate relationships, d760 Formal relationships, and d870 Economic self-sufficiency. Conclusion: The importance of social life aspects to the QoL was highlighted based on responses of SCI/D patients, clearly demonstrated through the ICF linking process. Adding a satisfaction with social life item to the QoL-BDS has made this instrument a more comprehensive measure.</p

Unconfined Aquifer Flow Theory - from Dupuit to present

Analytic and semi-analytic solution are often used by researchers and practicioners to estimate aquifer parameters from unconfined aquifer pumping tests. The non-linearities associated with unconfined (i.e., water table) aquifer tests makes their analysis more complex than confined tests. Although analytical solutions for unconfined flow began in the mid-1800s with Dupuit, Thiem was possibly the first to use them to estimate aquifer parameters from pumping tests in the early 1900s. In the 1950s, Boulton developed the first transient well test solution specialized to unconfined flow. By the 1970s Neuman had developed solutions considering both primary transient storage mechanisms (confined storage and delayed yield) without non-physical fitting parameters. In the last decade, research into developing unconfined aquifer test solutions has mostly focused on explicitly coupling the aquifer with the linearized vadose zone. Despite the many advanced solution methods available, there still exists a need for realism to accurately simulate real-world aquifer tests

Health-related quality of life among individuals with long-standing spinal cord injury: a comparative study of veterans and non-veterans

<p>Abstract</p> <p>Background</p> <p>Spinal cord-injured (SCI) patients experience poor health-related quality of life (HRQOL) and they usually report lower HRQOL than the general population or population subgroups in Iran and elsewhere. The aim of this study was to compare HRQOL between veterans and non-veterans with SCI in Iran.</p> <p>Methods</p> <p>This was a cross-sectional study. HRQOL was measured using the 36-item Short Form Health Survey (SF-36). Thirty-nine male veterans and 63 non-veteran males with SCI were included in the study. Regression analyses were applied to determine the variables affecting physical and mental health-related quality of life among the patients.</p> <p>Results</p> <p>The male veterans had a lower HRQOL than the non-veterans with SCI. The differences were significant for all measures except for physical and social functioning. The greatest difference was observed for bodily pain (P = 0.001). The regression analysis results indicated that a longer time since injury was associated (P = 0.01) with better physical health-related quality of life (PCS), while being a veteran (P < 0.001) and having a spinal lesion in the cervical region (P = 0.001) were associated with poorer PCS. Older age (P < 0.001) and higher education (P = 0.01) were associated with better mental health-related quality of life (MCS), while being a veteran and having a spinal lesion in the cervical region (P = 0.02) were associated with poorer MCS.</p> <p>Conclusion</p> <p>The study findings showed that veterans with SCI experienced lower HRQOL than their non-veteran counterparts. A qualitative study is recommended to evaluate why HRQOL was lower in veterans than in non-veterans with SCI although veterans had higher incomes as a result of their pensions and increased access to equipment, and medications. To improve quality of life in both veterans and non-veterans with spinal cord injuries, policy changes or implementation of new interventions may be essential so that veterans could receive additional support (e.g. counseling, recreation therapy, vocational therapy, etc.) and non-veterans could meet their basic needs.</p