scholarly journals Design of biomimetic fibrillar interfaces: 2. Mechanics of enhanced adhesion

2004 ◽  
Vol 1 (1) ◽  
pp. 35-48 ◽  
Author(s):  
C.-Y. Hui ◽  
N. J. Glassmaker ◽  
T. Tang ◽  
A. Jagota
Keyword(s):  
Interfacial Strength ◽  
Load Sharing ◽  
Adhesive Contact ◽  
Work Of Adhesion ◽  
Cross Sectional ◽  
Flat Interface ◽  
Dimensionless Function ◽  
The Stability ◽  
Fibril Length ◽  
Perfect Interface

This study addresses the strength and toughness of generic fibrillar structures. We show that the stress σ c required to pull a fibril out of adhesive contact with a substrate has the form σ c = σ 0 Φ( χ ). In this equation, σ 0 is the interfacial strength, Φ( χ ) is a dimensionless function satisfying 0=Φ( χ )=1 and χ is a dimensionless parameter that depends on the interfacial properties, as well as the fibril stiffness and radius. Pull-off is flaw sensitive for χ ≫1, but is flaw insensitive for χ <1. The important parameter χ also controls the stability of a homogeneously deformed non-fibrillar (flat) interface. Using these results, we show that the work to fail a unit area of fibrillar surface can be much higher than the intrinsic work of adhesion for a flat interface of the same material. In addition, we show that cross-sectional fibril dimensions control the pull-off force, which increases with decreasing fibril radius. Finally, an increase in fibril length is shown to increase the work necessary to separate a fibrillar interface. Besides our calculations involving a single fibril, we study the concept of equal load sharing (ELS) for a perfect interface containing many fibrils. We obtain the practical work of adhesion for an idealized fibrillated interface under equal load sharing. We then analyse the peeling of a fibrillar surface from a rigid substrate and establish a criterion for ELS.

scholarly journals Low back pain in physiotherapy students: Prevalence and the association with neuromuscular findings

2013 ◽  
Vol 69 (4) ◽  
Author(s):  
E. Burger ◽  
H. Myezwa ◽  
V. Naidoo ◽  
B. Olivier ◽  
A. Rothberg
Keyword(s):  
Low Back Pain ◽  
Back Pain ◽  
Cross Sectional Study ◽  
Transversus Abdominis ◽  
Low Back ◽  
Cross Sectional ◽  
Active Involvement ◽  
Optimal Function ◽  
The Stability ◽  
Physiotherapy Students

Background: Physiotherapy students are prone to low back pain (LBP) due to studying and their active involvement in clinical treatment of patients. As a result of pathology, muscle activity is influenced, affecting optimal function of the spine. Method: Physiotherapy students enrolled for 2010 at the University of the Witwatersrand participated in a cross-sectional study. A questionnaire and physical assessment were completed. Results: The study revealed that the lifetime LBP prevalence was 36% among physiotherapy students. Associations with LBP were hours of practical exposure, posterior-anterior mobilisations on L4 (p=0.003) and L5 (p≤0.001) centrally and unilaterally, left lumbar multifidus (LM) cross-sectional area (p=0.02), right obliquus internusabdominis (OI) (p=0.02) and right transversus abdominis (TrA) thickness at rest (p=0.02), as well as the pull of the TrA during contraction on the left (p=0.03). Discussion: Hours of practical exposure may play a role in lumbar pathology. Due to pathology, muscle imbalances of LM, TrA and OI affect the stability of the spine which may lead to recurrences. Conclusion: Practical exposure as well as LM, TrA and OI muscle imbalances were associated with LBP in physiotherapy students. Awareness of the factors associated with LBP while studying at an undergraduate level may lead to better prevention of LBP.

scholarly journals Glacial lake drainage: a stability analysis

1997 ◽  
Vol 24 ◽  
pp. 175-180
Author(s):  
Krzysztof Szilder ◽  
Edward P. Lozowski ◽  
Martin J. Sharp
Keyword(s):  
Differential Equations ◽  
Water Flow ◽  
Frictional Heating ◽  
Initial Perturbation ◽  
Tunnel Wall ◽  
Cross Sectional ◽  
Linear Ordinary Differential Equations ◽  
Simplifying Assumptions ◽  
Lake Drainage ◽  
The Stability

A model has been formulated to determine the stability regimes for water flow in a Subglacial conduit draining from a reservoir. The physics of the water flow is described with a set of differential equations expressing conservation of mass, momentum and energy. Non-steady flow of water in the conduit is considered, the conduit being simultaneously enlarged by frictional heating and compressed by plastic deformation in response to the pressure difference across the tunnel wall. With the aid of simplifying assumptions, a mathematical model has been constructed from two time-dependent, non-linear, ordinary differential equations, which describe the time evolution of the conduit cross-sectional area and the water depth in the reservoir. The model has been used to study the influence of conduit area and reservoir levels on the stability of the water flow for various glacier and ice-sheet configurations. The region of the parameter space where the system can achieve equilibrium has been identified. However, in the majority of cases the equilibrium is unstable, and an initial perturbation from equilibrium may lead to a catastrophic outburst of water which empties the reservoir.

scholarly journals Scale of adverse events associated to nursing practices: a psychometric study in Portuguese hospital context

2018 ◽  
Vol 26 ◽  
Author(s):  
Teresa Neves ◽  
Vitor Rodrigues ◽  
João Graveto ◽  
Pedro Parreira
Keyword(s):  
Adverse Events ◽  
Public Hospital ◽  
Hospital Setting ◽  
Cross Sectional Study ◽  
Cross Sectional ◽  
Stable Factor ◽  
Hospital Units ◽  
Northern Regions ◽  
Structural Invariance ◽  
The Stability

Objective to contribute to the validation study of the Scale of Adverse Events associated with Nursing Practices in the hospital context. Method cross-sectional study, in public hospital units, in the central and northern regions of Portugal. The exploratory factor analysis of the Scale of Adverse Events associated to Nursing Practices was conducted with a sample of 165 nurses and the confirmatory factorial analysis was made with a sample of 685 nurses. Reliability, internal consistency and construct validity were estimated. The invariance of the model was evaluated in two subsamples to confirm the stability of the factorial solution. Results the global sample consisted of 850 nurses aged between 22 and 59, mostly licensed professionals. The model had a good overall fit in the subscales (Nursing Practices: χ2/df = 2.88, CFI = 0.90, GFI = 0.86, RMSEA = 0.05, MECVI = 3.30; Adverse Events: χ2/df = 4.62, CFI = 0.93, GFI = 0.95, RMSEA = 0.07, MECVI = 0.39). There was a stable factor structure, indicating strong invariance in the subscale Nursing Practices and structural invariance in the subscale Adverse Events. Conclusion the refined model of the Scale of Adverse Events associated with Nursing Practices revealed good fit and stability of the factorial solution. The instrument was adjusted to evaluate the perception of nurses about adverse events associated with health care, precisely nursing care, in the hospital setting.

Al Doped Ta2O5 Thin Films for Microelectronic Applications

2000 ◽  
Vol 654 ◽  
Author(s):  
P. C Joshi ◽  
M. W. Cole ◽  
C. W. Hubbard ◽  
E. Ngo
Keyword(s):  
Thin Films ◽  
Precursor Solution ◽  
Electrical Measurements ◽  
Cross Sectional ◽  
Solution Deposition ◽  
Atomic Force ◽  
The Stability ◽  
Insulating Properties ◽  
Post Deposition

AbstractIn this paper, we report on the fabrication and characterization of pure and Al doped Ta2O5 thin films fabricated by metalorganic solution deposition (MOSD) technique. The pure and Aldoped Ta2O5 thin films were fabricated by spin-coating technique using room temperature processed carboxylate-alkoxide precursor solution. The structure of the films was analyzed by xray diffraction (XRD). The surface and cross-sectional morphology of the films were examined by field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). The electrical measurements were conducted on films in MIM configuration using Pt as the top and bottom electrode. The effects of Al concentration and the post-deposition annealing temperature on the structural, dielectric, and insulating properties were analyzed. The effects of the applied bias and the measurement temperature on the dielectric and insulating properties were also analyzed to establish the stability and reliability of Al doped Ta2O5 thin films.

The stability of pendent liquid drops. Part 1. Drops formed in a narrow gap

1973 ◽  
Vol 59 (4) ◽  
pp. 753-767 ◽  
Author(s):  
E. Pitts
Keyword(s):  
Contact Angles ◽  
Two Dimensional ◽  
Narrow Gap ◽  
Cross Sectional ◽  
Liquid Drops ◽  
Maximum Area ◽  
Area Increase ◽  
Equilibrium Profiles ◽  
The Stability ◽  
Horizontal Support

We consider a drop of liquid hanging from a horizontal support and sandwiched between two vertical plates separated by a very narrow gap. Equilibrium profiles of such ‘two-dimensional’ drops were calculated by Neumann (1894) for the case when the angle of contact between the liquid and the horizontal support is zero. This paper gives the equilibrium profiles for other contact angles and the criterion for their stability. Neumann showed that, as the drop height increases, its cross-sectional area increases until a maximum is reached. Thereafter, as the height increases, the equilibrium area decreases. This behaviour is shown to be typical of all contact angles. When the maximum area is reached, the total energy is a minimum. It is shown that the drops are stable as long as the height and the area increase together.

scholarly journals HYDRAULICS AND SEDIMENTARY STABILITY OF COASTAL INLETS

1972 ◽  
Vol 1 (13) ◽  
pp. 38 ◽  
Author(s):  
M.P. O'Brien ◽  
R.G. Dean
Keyword(s):  
Cross Section ◽  
Stability Index ◽  
Hydraulic Loss ◽  
Cross Sectional ◽  
Equilibrium Relationship ◽  
Depositional Patterns ◽  
Storage Area ◽  
Loss Coefficients ◽  
The Stability ◽  
Coastal Inlets

A method is presented for investigating the stability of coastal inlets against closure due to transport and deposition of sand in the inlet cross-section. The method utilizes earlier contributions by: (1) Keulegan representing the hydraulics of inlets, (2) O'Brien which describes an equilibrium relationship between the cross-sectional area of an inlet and the bay tidal prism, and (3) Escoffier which relates to the stability of an inlet under changes in conditions which tend to close or enlarge an inlet. A "stability index" is defined which incorporates the buffer storage area available in the inlet cross-section, prior to the onset of closure and also includes the capability of the inlet to transport excess sand from its cross-section. In order to apply the method, geometric and hydraulic data representing the inlet are necessary; the minimum data required include a survey of the inlet throat cross-section and the lag between high (or low) water in the ocean and the following slack water in the inlet. In addition, it is necessary to conduct measurements or make assumptions concerning the minor and gradual hydraulic loss coefficients. Based on assumed depositional patterns in the inlet, the method is applied to five real inlets and the stability indices are presented.

scholarly journals The steady motion and stability of a helical vortex

1928 ◽  
Vol 120 (786) ◽  
pp. 670-690 ◽  
Keyword(s):  
Reynolds Number ◽  
Vortex Motion ◽  
Steady Motion ◽  
Vortex Rings ◽  
Cross Sectional ◽  
Flow Past A Cylinder ◽  
Two Dimensional Flow ◽  
The Stability ◽  
Sectional Shape ◽  
Stable Formation

1. Introductory .—This is the third of a series of papers dealing with the stability or instability of certain forms of vortex motion associated with the wake of a body moving in a fluid. In the earlier papers we examined the case of a system of equal vortex rings in parallel planes, as they might form in the rear of a sphere in steady motion. Nisi and Porter have shown that the lowest speed at which the vortex ring forms is 8·14 v / d where v is the kinematic viscosity of the fluid and d is the diameter of the sphere. Such a system of vortices has been proved to be only partially stable, and it is therefore to be inferred that their production occurs at a transition stage to a more stable type of flow. Now it is well known that in the case of two dimensional flow past a cylinder of any cross-sectional shape, eddies are formed in symmetrical pairs at low values of Reynolds' number, whereas at higher values asymmetry sets in and the eddying is formed alternately at one side of the cylinder and then at the other with regular periodicity. This latter stage occurs over a range of values of Reynolds’ number extending from about 70 to 10 5 . Detailed explorations of the field for some distance behind the cylinder have established that the centres of eddying approximately assume the stable formation which has come to be known as the “Kármán vortex street."

Changes in adult children's participation in parent care

2012 ◽  
Vol 33 (4) ◽  
pp. 667-697 ◽  
Author(s):  
MAXIMILIANE E. SZINOVACZ ◽  
ADAM DAVEY
Keyword(s):  
Child Care ◽  
Adult Child ◽  
Care Giver ◽  
Cross Sectional ◽  
Pooled Data ◽  
Care Givers ◽  
Care Giving ◽  
The Us ◽  
And Gender ◽  
The Stability

ABSTRACTCare-giving research has focused on primary care-givers and relied on cross-sectional data. This approach neglects the dynamic and systemic character of care-giver networks. Our analyses address changes in care-givers and care networks over a two-year period using pooled data from the US Health and Retirement Study, 1992–2000. Based on a matrix of specific adult-child care-givers across two consecutive time-points, we assess changes in any adult-child care-giver and examine the predictors of change. A change in care-giver occurred in about two-fifths of care-giving networks. Ability to provide care based on geographical proximity, availability of alternative care-givers, and gender play primary roles in the stability of care networks. Results underline the need to shift care-giving research toward a dynamic and systemic perspective.

The Stability of Global and Specific Measures of the Fear of Crime: Results from a Two Wave Trinidadian Longitudinal Study

2003 ◽  
Vol 10 (1) ◽  
pp. 49-70 ◽  
Author(s):  
Jason Ditton ◽  
Derek Chadee ◽  
Furzana Khan
Keyword(s):  
Longitudinal Study ◽  
Survey Data ◽  
Fear Of Crime ◽  
Longitudinal Survey ◽  
Cross Sectional ◽  
National Surveys ◽  
Important Measure ◽  
British Crime Survey ◽  
The Stability

The ‘fear of crime’ is a politically important measure, and much is made of year to year changes in levels when generated by repeat cross-sectional national surveys such as the British Crime Survey. Data from the first two waves of a longitudinal survey of the fear of crime undertaken in Trinidad indicate that identical year on year fear levels regularly conceal considerable gross changes in reported fear, many of which are mutually cancelled in the calculation of net year- on-year fear levels. These results question either or both of the stability of the fear of crime, and of measures used to assess it.

Importance of Added Mass for the Interaction Between IL and CF Vibrations of Free Spanning Pipelines

2011 ◽  
Author(s):  
Ida M. Aglen ◽  
Carl M. Larsen
Keyword(s):  
Cross Sections ◽  
Amplitude Ratio ◽  
Large Diameter ◽  
Cross Flow ◽  
Added Mass ◽  
Flexible Beam ◽  
Hydrodynamic Coefficients ◽  
Cross Sectional ◽  
Mass Coefficient ◽  
The Stability

The importance of cross-flow (CF) response generated by vortex induced vibrations (VIV) of free spanning pipelines has long been recognised. The significance of in-line (IL) vibrations has recently been understood and hence also been subjected to research. The combined effect of CF and IL vibrations is, however, still not fully described. This paper highlights the CF-IL interaction with focus on the transition zone from pure IL to CF dominated response, giving special attention to how the added mass influences the interaction. Results from extensive flexible beam tests connected to the Ormen Lange (OL) development have been used as a basis for this study. Trajectories for cross sectional motions from the flexible beam test were identified, and then used as forced motions of a large diameter rigid cylinder exposed to uniform flow. Non-dimensional parameters like Reynolds number (Re), amplitude ratio and reduced frequency were identical for the two tests. Hence, forces found from the forced motion test could be used to find hydrodynamic coefficients valid for the flexible beam case. This paper discusses the results from the flexible beam tests with a relatively short length to diameter ratio (L/D) of 145. Modal analyses by Nielsen et al. (2002) show that the first mode dominates in both directions for these particular tests, even though the IL response frequency is twice the CF frequency. In this paper the added mass variations along the OL flexible beam is studied. Forces acting on 4 different cross sections along the beam are measured for 7 different prototype velocities. For each test the hydrodynamic coefficients are calculated, and the results show how the added mass changes along the beam for increasing velocities, and thereby creates resonance for both IL and CF response. The stability of the added mass coefficient throughout the time series is also evaluated.

Sign in / Sign up

Export Citation Format

Share Document