A Minimal Model for Vorticity and Gradient Banding in Complex Fluids

A general phenomenological reaction-diffusion model for flow-induced phase transitions in complex fluids is presented. The model consists of an equation of motion for a nonconserved composition variable, coupled to a Newtonian stress relations for the reactant and product species. Multivalued reaction terms allow for different homogeneous phases to coexist with each other, resulting in banded composition and shear rate profiles. The one-dimensional equation of motion is evolved from a random initial state to its final steady-state. We find that the system chooses banded states over homogeneous states, depending on the shape of the stress constitutive curve and the magnitude of the diffusion coefficient. Banding in the flow gradient direction under shear rate control is observed for shear-thinning transitions, while banding in the vorticity direction under stress control is observed for shear-thickening transitions.Comment: 11 pages, submitted to Eur Phys J

Two-state shear diagrams for complex fluids in shear flow

The possible "phase diagrams'' for shear-induced phase transitions between two phases are collected. We consider shear-thickening and shear-thinning fluids, under conditions of both common strain rate and common stress in the two phases, and present the four fundamental shear stress vs. strain rate curves and discuss their concentration dependence. We outline how to construct more complicated phase diagrams, discuss in which class various experimental systems fall, and sketch how to reconstruct the phase diagrams from rheological measurements

“Do or Die”- Learning Science Diplomacy from the Father of our Nation

14-15On 8th August 1942, on the eve of the launch of the Quit India movement, Mahatma Gandhi made a historic statement “Here is a Mantra, a short one, that I give you. You may imprint it on your hearts and let every breath of yours give expression to it. The mantra is: ‘Do or Die’.

Sustainable Quality of Work Life and Job Satisfaction [an Indian Case Study]

As HR experts would propound, organizational success is highly dependent on attracting, recruiting, motivating, and retaining its workforce. The quality of work life (QWL) pertains to favourable or unfavourable work environment in keeping employees motivated so as to enable increase per capita productivity. It aims at achieving an effective work place environment that satisfies  both the organizational and personal needs and values of employees , promoting well being by job security,  job satisfaction, development and thereby helping to maintain a better  balance between work and non-work life. The word sustainability is derived from the Latin sustinere (tenere, to hold; sus, meaning up. Dictionaries provide more than ten meanings for sustain, the main ones being to “maintain", "support", or "endure”. However, since the 1980s sustainability has been used more in the sense of human sustainability on planet Earth and this has resulted in the most widely quoted definition of sustainability as a part of the concept sustainable, that of the Brundtland Commission of the United Nations on March 20, 1987: “sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their needs.

A qualitative exploration of attitudes towards the use of outcome measures in child and adolescent mental health services

The aim of the present research was to explore clinician attitudes to outcome measures and, in particular, the facilitators and barriers to implementing outcome measures. An up-to-date exploration of clinician attitudes is especially needed in the context of recent policies on the implementation of outcome measures in child and adolescent mental health services (CAMHS), and because evidence suggests that there is a disparity between policy recommendations and the use of outcome measures in clinical practice. Semi-structured interviews were conducted with nine CAMHS clinicians from a Mental Health Trust in South London. Two levels of implementation emerged from the analysis: (1) the service level, regarding the implementation of outcome measures across a service to inform service improvement and (2) the session level, regarding the implementation of outcome measures within individual clinical sessions. The present research described training and ongoing support as a crucial facilitator of use at both service and session levels. This included help overcoming local contextual barriers, such as resources, information systems and administrative processes. The research showed that a balance is needed between a mandatory and uniform approach across a service and providing clinicians with support to use outcome measures with all service users for whom they are appropriate

Temporal Progression of Aortic Valve Pathogenesis in a Mouse Model of Osteogenesis Imperfecta.

Organization of extracellular matrix (ECM) components, including collagens, proteoglycans, and elastin, is essential for maintaining the structure and function of heart valves throughout life. Mutations in ECM genes cause connective tissue disorders, including Osteogenesis Imperfecta (OI), and progressive debilitating heart valve dysfunction is common in these patients. Despite this, effective treatment options are limited to end-stage interventions. Mice with a homozygous frameshift mutation in col1a2 serve as a murine model of OI (oim/oim), and therefore, they were used in this study to examine the pathobiology of aortic valve (AoV) disease in this patient population at structural, functional, and molecular levels. Temporal echocardiography of oim/oim mice revealed AoV dysfunction by the late stages of disease in 12-month-old mice. However, structural and proteomic changes were apparent much earlier, at 3 months of age, and were associated with disturbances in ECM homeostasis primarily related to collagen and proteoglycan abnormalities and disorganization. Together, findings from this study provide insights into the underpinnings of late onset AoV dysfunction in connective tissue disease patients that can be used for the development of mechanistic-based therapies administered early to halt progression, thereby avoiding late-stage surgical intervention

Rheological Chaos in a Scalar Shear-Thickening Model

We study a simple scalar constitutive equation for a shear-thickening material at zero Reynolds number, in which the shear stress \sigma is driven at a constant shear rate \dot\gamma and relaxes by two parallel decay processes: a nonlinear decay at a nonmonotonic rate R(\sigma_1) and a linear decay at rate \lambda\sigma_2. Here \sigma_{1,2}(t) = \tau_{1,2}^{-1}\int_0^t\sigma(t')\exp[-(t-t')/\tau_{1,2}] {\rm d}t' are two retarded stresses. For suitable parameters, the steady state flow curve is monotonic but unstable; this arises when \tau_2>\tau_1 and 0>R'(\sigma)>-\lambda so that monotonicity is restored only through the strongly retarded term (which might model a slow evolution of material structure under stress). Within the unstable region we find a period-doubling sequence leading to chaos. Instability, but not chaos, persists even for the case \tau_1\to 0. A similar generic mechanism might also arise in shear thinning systems and in some banded flows.Comment: Reference added; typos corrected. To appear in PRE Rap. Com

Bulk and Interfacial Shear Thinning of Immiscible Polymers

Nonequilibrium molecular dynamics simulations are used to study the shear thinning behavior of immiscible symmetric polymer blends. The phase separated polymers are subjected to a simple shear flow imposed by moving a wall parallel to the fluid-fluid interface. The viscosity begins to shear thin at much lower rates in the bulk than at the interface. The entire shear rate dependence of the interfacial viscosity is consistent with a shorter effective chain length $s^*$ that also describes the width of the interface. This $s^*$ is independent of chain length $N$ and is a function only of the degree of immiscibility of the two polymers. Changes in polymer conformation are studied as a function of position and shear rate.Shear thinning correlates more closely with a decrease in the component of the radius of gyration along the velocity gradient than with elongation along the flow. At the interface, this contraction of chains is independent of $N$ and consistent with the bulk behavior for chains of length $s^*$. The distribution of conformational changes along chains is also studied. Central regions begin to stretch at a shear rate that decreases with increasing $N$, while shear induced changes at the ends of chains are independent of $N$.Comment: 8 pages, 8 figure