Analysis of droplet evaporation on a superhydrophobic surface.

The evaporation process for small, 1-2-mm-diameter droplets of water from patterned polymer surfaces is followed and characterized. The surfaces consist of circular pillars (5-15 microm diameter) of SU-8 photoresist arranged in square lattice patterns such that the center-to-center separation between pillars is 20-30 microm. These types of surface provide superhydrophobic systems with theoretical initial Cassie-Baxter contact angles for water droplets of up to 140-167 degrees, which are significantly larger than can be achieved by smooth hydrophobic surfaces. Experiments show that on these SU-8 textured surfaces water droplets initially evaporate in a pinned contact line mode, before the contact line recedes in a stepwise fashion jumping from pillar to pillar. Provided the droplets of water are deposited without too much pressure from the needle, the initial state appears to correspond to a Cassie-Baxter one with the droplet sitting upon the tops of the pillars. In some cases, but not all, a collapse of the droplet into the pillar structure occurs abruptly. For these collapsed droplets, further evaporation occurs with a completely pinned contact area consistent with a Wenzel-type state. It is shown that a simple quantitative analysis based on the diffusion of water vapor into the surrounding atmosphere can be performed, and estimates of the product of the diffusion coefficient and the concentration difference (saturation minus ambient) are obtained.

Topography driven spreading.

Roughening a hydrophobic surface enhances its nonwetting properties into superhydrophobicity. For liquids other than water, roughness can induce a complete rollup of a droplet. However, topographic effects can also enhance partial wetting by a given liquid into complete wetting to create superwetting. In this work, a model system of spreading droplets of a nonvolatile liquid on surfaces having lithographically produced pillars is used to show that superwetting also modifies the dynamics of spreading. The edge speed-dynamic contact angle relation is shown to obey a simple power law, and such power laws are shown to apply to naturally occurring surfaces.

The efficacy and safety of cefaclor in respiratory infections amongst Pakistani children.

PURPOSE: To evaluate the efficacy and safety of Cefaclor in respiratory tract infections amongst Pakistani children. PATIENTS AND METHODS: Multicenter, open label and non-comparative study was done to evaluate the response in terms of symptoms (In vivo) and bacterial cultures (In Vitro) to Cefaclor amongst children with respiratory tract infection between the ages 2 months to 12 years. Each patient was asked to visit the doctor on three occasions i.e., Day 0 (Initial evaluation prior to commencement of study), Day 4 (During therapy assessment and confirmation of compliance) and Day 10 (End of therapy assessment and compliance evaluation). Representative swab specimens (Throat swabs, Ear swabs or Sputum) were collected from the infected site on day 0 and day 10 for culture and sensitivity. Patients were also assessed by the evaluators on each visit in terms of clinical symptomatic response and information collected was documented on a prescribed data base form. RESULTS: A total of 160 patients were enrolled in the study, of whom 15 were lost to follow-up between the first and second visit and a further 38 were lost by the 3rd visit. Thus 107 patients completed the study as per protocol. Otitis media and Upper respiratory tract infection were the predominant ailments amongst the cases enrolled. One or more bacteria were isolated in 75 (46%) instances, the maximum number of isolates being from ear swabs of Otitis media patients. Beta haemolytic Streptococcus (group A,C,F,G) seen in 18 cases was the most common pathogen reported followed by Staphylococcus aureus, H. influenzae and Streptococcus pneumoniae in 13,12 and 11 cases respectively. Sensitivity of Cefaclor for bacteria commonly seen in the respiratory tract was greater than 90% in most of the cases. Evaluation of the 42 culture proven cases for patients who completed the study showed that Cefaclor had a 93% efficacy for indicated bacteria and 54% for non-indicated bacteria. In Vivo analysis of Cefaclor (i.e. on the basis of symptomatic response) showed that 96% cases had a symptomatic response by the second visit, which improved to 97% by the third visit. Only 15 non-serious adverse events were observed in 160 patients, none of the cases necessitated discontinuation of drug. Mild gastrointestinal symptom was the most common adverse event reported. CONCLUSION: Cefaclor was found to be a safe and efficacious drug in the treatment of bacterial respiratory tract infections amongst Pakistani children.