Flow Visualization During Droplet Evaporation on Hydrophobic and Superhydrophobic Surfaces

The flow behavior inside an evaporating droplet on a hydrophobic (initial contact angle ~120 deg) and superhydrophobic surface (initial contact angle ~ 150 deg) is studied using Particle Image Velocimetry (PIV). Water droplets (with initial volume ~ 3 μL) are considered with suspended fluorescent polystyrene particles for visualization. An axisymmetric counter-rotating vortex pair is observed in the vertical plane of the droplet as it evaporates on the hydrophobic surface. The flow direction is upwards along the vertical axis of the droplet signifying a buoyancy-induced flow field. A single-directional vortex structure occurs in the droplet evaporating on superhydrophobic surface. An image-correction algorithm based on the ray-tracing technique is employed to correct the distortion caused due to refraction of light at the surface of the droplet, and yield an accurate quantitative estimation of the velocity vectors. Centrally localized deposition of suspended particles observed for droplet evaporation on hydrophobic and superhydrophobic surfaces as opposed to the circumferential deposition seen in the case of hydrophilic surfaces is explained in terms of the observed convection flow characteristics

Evaporation-Driven Micromixing in Sessile Droplets for Miniaturized Absorbance-Based Colorimetry

We demonstrate the use of an evaporating, sessile droplet on a nonwetting substrate as a miniature micromixing device to conduct sample−dye reactions for absorbance-based colorimetry. The nonwetting substrate supports buoyancy-induced mixing inside the droplet for rapid completion of the measurement. The Bradford assay is used as a proof of concept, where a protein-containing sample is reacted with a reagent dye to measure the protein concentration. Viability of absorbance measurement through the droplet is first established using droplets in which the reactants are mixed prior to their deposition onto the substrate. In a second set of experiments involving in situ mixing, the reagent is directly added to a sessile droplet of the protein-containing sample, allowing the reactants to mix while the absorbance is being measured. Interplay between buoyancyinduced mixing, protein−reagent reaction, and protein adsorption onto the substrate leads to a complex temporal absorbance measurement signal. Videos corresponding to the signal data show that each of these mechanisms dominates during different phases of droplet evolution, causing a signal pattern containing peaks and valleys having a strong monotonic trend with the protein concentration. Overall, the second absorbance peak at which the reaction nears completion is the most sensitive to sample concentration. Heating of the substrate is demonstrated to dramatically speed up the mixing process. These protein concentration measurements, obtained with a simpler system and low reactant volumes, demonstrate that this droplet micromixing concept is a viable alternative to microtiter plates for colorimetric applications

Development of MgAl2O4 grain refiner in Al in-situ composite through H3BO3 addition

Abstract : In the present work, a novel approach has been made for synthesis of in-situ Magnesium Aluminate (MgAl2O4) particles in the Al-4Mg alloy by Boric Acid (H3BO3) precursor addition (1 wt %, 1.5 wt % and 2 wt %) during the casting process. The developed composite has been investigated for its microstructural characteristics and corrosion performance. Scanning Electron Microscopy and Energy Dispersive Spectroscopy examination revealed the formation of MgAl2O4 particles in the composite. Potentiodynamic polarization corrosion experiments were performed on the Al-4Mg/H3BO3 composite specimens (1 wt %, 1.5 wt % and 2 wt %) in three different medium (3.5 % Sodium Chloride-NaCl, 1 M Sulphuric Acid-H2SO4 and 1 M Hydrochloric Acid-HCl). Corrosion results showed that Al-4Mg/1.5 wt % H3BO3 composite specimen exhibited better corrosion resistance in 3.5 % NaCl, 1 M H2SO4 and 1 M HCl medium due to the significant grain refinement produced by MgAl2O4 particles. The developed composite with better corrosion properties can be utilized for marine and naval application

Enhancement of Structural, Optical and Bumpy Surface Effect of Cu2O Thin Films Through Sn Doping by Modified SILAR Technique

Undoped and Sn doped Cu2-xSnxO (x = 0, 5.0, 10.0, 15.0 and 20.0) thin films have been deposited into glass substrates by hire a fee powerful method of M-SILAR (Modified-Successive Ionic Layer Adsorption and Reaction). The Sn doping level in the starting solution become numerous from 0 to 20.0 mol.% in steps of 5.0 mol.%. The deposited films were characterized for their structural, optical, morphological and topography properties with respective instrumentation. X-ray diffraction (XRD) evaluation found out the orientation of crystalline increase of Cu2-xSnxO films, and all the films showcase single crystalline. The preferential orientation was retained in favor of (111) plane even at the highest doping level. The presence of copper in the films turned into showed by way of energy dispersive X-ray spectrometer. Average optical transmittance (UV-vis-NIR and Photoluminescence (PL)) are varied with effect of doping concentration. The stretching vibrations of Cu-O, Sn-O and O-Cu-O have been showed by using Fourier transform infrared spectroscopy (FTIR). The morphological observe has been achieved by using a Field emission scanning electron microscopy (FE-SEM) has display as decrease the particle length with increase of doping concentration. From High resolution transition electron microscopy (HR-TEM) the crystalline growth of each line are excellent within the Sn doping of 10.0 mol.%. The atomic force microscopy method changed into employed to investigate the roughness of the films and the bumpy surface revealed at 10.0 mol.% of Sn doping level

COMPARATIVE PHYTOCHEMICAL PROFILE OF CRINUM DEFIXUM KER-GAWLER LEAVES USING GC-MS

The present investigation was carried out to determine the possible phytochemical compounds present in the various extracts of Crinum defixum Ker-Gawler leaves. It is an important medicinal plant worldwide trends towards the utilization of natural plant remedies has created an enormous need for the use of medicinal plants. Different pharmacological properties of C.defixum Ker-Gawler have already been reported. Thus, the present study was performed to investigate the preliminary phytochemical screening, separation, identification of compounds and compare the phytochemical composition of various fractions of C.defixum Ker-Gawler leaves using gas chromatography-mass spectrometry. The plant was extracted for various solvents in increasing order of polarity from using n-hexane, chloroform, ethyl acetate, acetone, ethanol, butanol and methanol. The extracts were subjected to GC-MS analysis and also confirmed by spectral analysis. Keywords: Crinum defixum Ker-Gawler, Phytochemical screening, Separation and identification of compounds, GC-MS, Spectral analysis

The Natural Progression of Gambiense Sleeping Sickness: What Is the Evidence?

Gambiense human African trypanosomiasis (HAT, sleeping sickness) is widely assumed to be 100% pathogenic and fatal. However, reports to the contrary exist, and human trypano-tolerance has been postulated. Furthermore, there is uncertainty about the actual duration of both stage 1 and stage 2 infection, particularly with respect to how long a patient remains infectious. Understanding such basic parameters of HAT infection is essential for optimising control strategies based on case detection. We considered the potential existence and relevance of human trypano-tolerance, and explored the duration of infectiousness, through a review of published evidence on the natural progression of gambiense HAT in the absence of treatment, and biological considerations. Published reports indicate that most gambiense HAT cases are fatal if untreated. Self-resolving and asymptomatic chronic infections probably constitute a minority if they do indeed exist. Chronic carriage, however, deserves further study, as it could seed renewed epidemics after control programmes cease

Spatiotemporal Infrared Measurement of Interface Temperatures During Water Droplet Evaporation on a Nonwetting Substrate

High-fidelity experimental characterization of sessile droplet evaporation is required to understand the interdependent physical mechanisms that drive the evaporation. In particular, cooling of the interface due to release of the latent heat of evaporation, which is not accounted for in simplified vapor-diffusion-based models of droplet evaporation, may significantly suppress the evaporation rate on nonwetting substrates, which support tall droplet shapes. This suppression is counteracted by convective mass transfer from the droplet to the air. While prior numerical modeling studies have identified the importance of these mechanisms, there is no direct experimental evidence of their influence on the interfacial temperature distribution. Infrared thermography is used here to simultaneously measure the droplet volume, contact angle, and spatially resolved interface temperatures for water droplets on a nonwetting substrate. The technique is calibrated and validated to quantify the temperature measurement accuracy; a correction is employed to account for reflections from the surroundings when imaging the evaporating droplets. Spatiotemporally resolved interface temperature data, obtained via infrared thermography measurements, allow for an improved prediction of the evaporation rate and can be utilized to monitor temperature-controlled processes in droplets for various lab-on-a-chip applications

2-(1,2,3,4-Tetra­hydro-9H-carbazol-1-yl­idene)propane­dinitrile

In the title compound, C15H11N3, the cyclo­hexene ring adopts a sofa conformation. An intra­molecular N—H⋯N hydrogen bond generates an S(7) ring motif. In the crystal, mol­ecules are linked by inter­molecular N—H⋯N, C—H⋯N and C—H⋯π inter­actions into a three-dimensional network

Haemoglobin and haematocrit: is the threefold conversion valid for assessing anaemia in malaria-endemic settings?

BACKGROUND: Anaemic status is determined by haemoglobin using the HemoCue system or haematocrit measurements, and a threefold conversion is commonly used to equate the two measures (haemoglobin = haematocrit/3). The validity of this conversion in malaria endemic settings was assessed. METHODS: Concurrent measures of haemoglobin and centrifuged haematocrit in children aged 6-59 months were compared by modelling the difference between the two measures against their average. A random effects linear regression of the difference of the measures on their average was used to describe the line of best agreement and 95% limits of agreement for these two measures over a range of values after adjusting for statistically significant covariates. RESULTS: There was a consistent bias between the two measures, with haemoglobin less than haematocrit/3 in 87% (899/1,030) of observations. This difference was non-uniform, decreasing with the average measure, i.e. less difference at higher haemoglobin and haematocrit values. In these studies, use of haematocrit would have underestimated the prevalence of anaemia by misclassifying 10% (89/920) of individuals with haemoglobin < 11 g/dl, 66% (252/380) of individuals with haemoglobin < 8 g/dl and 100% (23/23) of individuals with haemoglobin < 5 g/dl. The mean difference between the measures was greater in males than females, increased with age between 6-59 months, and was greater in the wet than dry season suggesting that the relationship between haemoglobin and haematocrit may be modified by exposure to malaria. CONCLUSION: The regression model indicated that the standard threefold conversion from haematocrit to haemoglobin underestimates the prevalence of haemoglobin < 11 g/dl in children under five years of age in malaria endemic settings. This bias was more acute for more severe anaemia defined by haemoglobin < 8 g/dl and haemoglobin < 5 g/dl. This has important implications for the comparability of studies using these different measures. Direct determination of haemoglobin should be the measurement of choice for assessing anaemia outcomes in malaria intervention trials and surveys