Molecular Approach for Understanding the Stability, Collision, and Coalescence of Bulk Nanobubbles.

Though long-lived nanobubbles (NBs) have been reported by multiple researchers, the underlying reason behind their stability is still obscure. Some of the conjectured reasons include diffusive shielding, the presence of surface charges, and stability due to contamination. Still, the stability of NBs against coalescence and Ostwald ripening is not confirmed. Using molecular dynamics simulations, the present study aims to understand the stabilization effects due to diffusive shielding and the presence of an electrical double layer at the surface of NBs. Accumulation of charges on NBs for different concentrations of ions is discussed. Also, the collision of equal-sized NBs with different approach velocities and offset distances is simulated. A regime map is predicted on the basis of initial approach velocity and offset distance. The transition in regime obtained upon increasing the offset distance is discussed, which differs from the collision characteristics of macroscopic bubbles and drops. The merging of NBs is initiated through the bridge formation, for which the temporal evolution rate along with the scaling argument is presented. The stress terms involved and the corresponding regimes are predicted based on the fluid properties. For all the cases where merging is observed, the estimated probability is observed to be low, which suggests the stability of NBs against coalescence.

Electric Charge-Induced Active Control of Nucleate and Rapid Film Boiling at the Nanoscale: a Molecular Perspective.

An effort has been made to understand the nucleate and the rapid film boiling phenomena under the influence of an electric field using a molecular viewpoint. The behavior of water molecules with a solid copper surface during the film boiling process in the presence of an electric field of different intensities has been studied. The molecular reasoning behind the suppression of the Leidenfrost phenomenon upon application of a uniform electric field along the heating substrate is established. Furthermore, the effect of surface characteristics with different wettabilities on film boiling in the presence of an electric field has also been studied. The electric field produces a finger-like water column besides thinning of the water film over a non-wetting surface. A similar phenomenon is also evident over a hydrophilic surface only after reaching a threshold value of electric charge intensity. Molecular simulations have explained the phenomenon of nucleate boiling of water on hydrophilic or non-wetting surfaces. Finally, the ability to control the bubble formation and suppression at a required location using an electric field has also been demonstrated. The water molecules near the surface experience dispersion at a lower electric field and an attraction force at a higher electric field, mimicking bubble nucleation and suppression, respectively.

Sunlight induced biosynthesis of silver nanoparticle from the bark extract of Amentotaxus assamica D.K. Ferguson and its antibacterial activity against Escherichia coli and Staphylococcus aureus.

Green synthesis of nanoparticles has gained importance due to its eco-friendly, low toxicity and cost effective nature. This study deals with the biosynthesis of silver nanoparticles (AgNPs) from the bark extract of Amentotaxus assamica. The AgNPs have been synthesised by reducing the silver ions into stable AgNPs using the bark extract of Amentotaxus assamica under the influence of sunlight irradiation. The characterisation of the biosynthesised AgNPs was carried out by UV-vis spectroscopy, X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray analysis. The UV-vis spectrum showed a broad peak at 472 nm. Also, the XRD confirmed the crystalline structure of the AgNPs. Moreover, the SEM analysis revealed that the biosynthesised AgNPs were spherical in shape. Also, dynamic light scattering techniques were used to evaluate the size distribution profile of the biosynthesised AgNPs. Furthermore, the biosynthesised AgNPs showed a prominent inhibitory effect against both Escherichia coli (MTCC 111) and Staphylococcus aureus (MTCC 97). Thus the biosynthesis of AgNPs from the bark extract of Amentotaxus assamica is found to eco-friendly way of producing AgNPs compared to chemical method.

Pachydermoperiostosis Mimicking Acromegaly: A Case Report.

Pachydermoperiostosis is a rare, hereditary disease commonly presenting with digital clubbing, pachyderma, and periosteal hypertrophy. Coarsening of facial features and spade-like enlargement of hands and feet may give rise to a diagnostic dilemma between pachydermoperiostosis and acromegaly. This report highlights a case of a 36-year-old man who presented with broadening of hands and feet, facial skin thickening, and edematous and drooping eyelids for the last 10 years. There was no history of similar presentation in his family. Such clinical presentation in corroboration with normal growth hormone level and prominent radiological abnormalities prompted us to make a diagnosis of pachydermoperiostosis.

Differential effects of community health worker visits across social and economic groups in Uttar Pradesh, India: a link between social inequities and health disparities.

BACKGROUND: Uttar Pradesh (UP) accounts for the largest number of neonatal deaths in India. This study explores potential socio-economic inequities in household-level contacts by community health workers (CHWs) and whether the effects of such household-level contacts on receipt of health services differ across populations in this state. METHODS: A multistage sampling design identified live births in the last 12 months across the 25 highest-risk districts of UP (N = 4912). Regression models described the relations between household demographics (caste, religion, wealth, literacy) and CHW contact, and interactions of demographics and CHW contact in predicting health service utilization (> = 4 antenatal care (ANC) visits, facility delivery, modern contraceptive use). RESULTS: No differences were found in likelihood of CHW contact based on caste, religion, wealth or literacy. Associations of CHW contact with receipt of ANC and facility delivery were significantly affected by religion, wealth and literacy. CHW contact increased the odds of 4 or more ANC visits only among non-Muslim women, increased the odds of both four or more ANC visits and facility delivery only among lower wealth women, increased the odds of facility delivery to a greater degree among illiterate vs. literate women. CONCLUSION: CHW visits play a vital role in promoting utilization of critical maternal health services in UP. However, significant social inequities exist in associations of CHW visits with such service utilization. Research to clarify these inequities, as well as training for CHWs to address potential biases in the qualities or quantity of their visits based on household socio-economic characteristics is recommended.

Single-mode instability of a ferrofluid-mercury interface under a nonuniform magnetic field.

This work reports an experimental and a numerical study of the interfacial instability in a mercury-ferrofluid system caused by a spatially nonuniform magnetic field against the action of gravity and interfacial tension. The interface evolution is observed to be continuous till its movement is hindered by a physical boundary. In contrast to the behavior of the ferrofluid interface under uniform field, we noted the instability growth to be monotonic under a field gradient. A steepness in the growth curve is noticed during the later stages of the instability, indicating a high magnitude of the growth velocities. Some unique phenomena, such as similarity of the growth at the initial stage, a slope transition in the growth curve at a later stage, and wrapping and pinning of the interface are observed, both in experiments and simulations.

Mechanism of Bursting Taylor Bubbles at Free Surfaces.

Collapse of a Taylor bubble inside a pipe at the free surface of a liquid is studied experimentally using speed imaging camera and illumination and subsequent image analysis. Three different fluids, water, glycerin, and silicone oil, are employed in the experiments. For all conditions studied herein, the bubble punctures at the free surface to form two thin films, i.e., one covering the cross-section of the tube near the free surface and one along the tube wall in the vertical direction. Surface tension acts to collapse the first film, which widens the punctured hole in the outward radial direction, thereby feeding the liquid in the vertical film. After the shrinking of the radial film, gravity causes the collapse of the vertical film, which generates a tiny jet of liquid at the end of collapse. Experiments with different fluids show a drastic change in shape and thickness of the vertical film that leads to higher drainage time. Analysis of time scale for the drainage of the horizontal film exhibits a favorable match with experiments. Finally, evolution of the vertical film is analyzed using a simple hydrodynamic model to estimate the order magnitude of time taken to collapse, which compares well with processed image data from experiments.

Evaluation of stepping stones as a tool for changing knowledge, attitudes and behaviours associated with gender, relationships and HIV risk in Karnataka, India.

BACKGROUND: Stepping Stones training aims to help individuals explore sexual relationships and recognize gender inequalities, the structural drivers of the HIV epidemic, in order to understand risk behaviours and to seek solutions to factors that increase HIV vulnerability. Despite earlier studies suggesting the success of Stepping Stones, little data exist to show diffusion to trainees' social networks or the wider community. METHODS: A mixed-methods evaluation of this approach was undertaken using in-depth interviews of trainees and friends, and polling booth surveys in 20 villages where Stepping Stones training took place and in another 20 villages with no Stepping Stones intervention. RESULTS: The interview respondents and their friends reported significant changes in their relationships after training, and benefit from discussion of gender, sexuality, condom use and HIV vulnerability issues. However, though diffusion of this knowledge at the level of personal contacts was strong, the evaluation revealed that diffusion to the community level was limited. CONCLUSIONS: The qualitative part of this study reflects other studies in different settings, in that SS participants gained immensely from the training. Wider behaviour change is a challenging goal that many programmes fail to attain, with most interventions too limited in scope and intensity to produce larger community effects. This may have contributed to the fact that we observed few differences between interventions and non-intervention villages in this study. However, it is also possible that we had excessive expectations of individual change at the community level, and that it might have been more appropriate to have had broader community level rather than individual behavioural change indicators. We suggest that SS could be enhanced by efforts to better engage existing community opinion leaders, to empower and train participants as community change agents, and to support the development of village-level action plans that combat sexual stereotyping and risky behaviours that lead to unhealthy sexual relationships.

Simulation of drop movement over an inclined surface using smoothed particle hydrodynamics.

Smoothed particle hydrodynamics (SPH) is used to numerically simulate the movement of drops down an inclined plane. Diffuse interfaces have been assumed for tracking the motion of the contact line. The asymmetric shape of the three-dimensional drop and the variation of contact angle along its periphery can be calculated using the simulation. During the motion of a liquid drop down an inclined plane, an internal circulation of liquid particles is observed due to gravitational pull which causes periodic change in the drop shape. The critical angle of inclination required for the inception of drop motion is also evaluated for different fluids as a function of drop volume. The numerical predictions exhibit a good agreement with the published experimental results.