A thermal cycling method, whereby capillary tubes holding polymerase chain reactions are subjected to programmed tilt displacements so that they are moved using gravity over three spatial regions (I, II, and III) kept at different constant temperatures to facilitate deoxyribonucleic acid (DNA) denaturation, annealing, and extension, is described. At tilt speeds in excess of 0.2 rad/s, the standard deviation of static coefficient of friction values was below 0.03, indicating in sync movement of multiple capillary tubes over the holding platform. The travel time during the acceleration phase and under constant velocity between adjacent regions (I to II and II to III) and distant regions (III to I) was 0.03 s and 0.31 s, respectively. The deviations in temperature did not exceed 0.05 °C from the average at the prescribed denaturing, annealing, and extension temperatures applied. DNA amplification was determined by optical readings, the fluorescence signal was found to increase twofold after 30 thermal cycles, and 1.16 × 106 DNA copies/μl could be detected. The approach also overcomes problems associated with thermal inertia, sample adhesion, sample blockage, and handling of the reaction vessels encountered in the other thermal cycling schemes used.
Highly
wetting and nonwetting substrates have been widely used
in fogwater collection systems for enhanced water harvesting. In this
work, fog harvesting substrates comprising PVC strips of different
wetting properties and widths ranging from 1–5 mm were vertically
aligned and spaced apart at regular intervals to give the same solid
area fraction of 0.8. Evaluation of the water collection efficiencies
of the tested configurations revealed that 1 mm wide superhydrophilic
strips was the most efficient, achieving double the amount of water
harvested compared with 2.8 mm wide strips. This finding was attributed
to the low Stokes numbers of the aerosol particle distribution of
the fog which tended to result in them being brought by the flow streamlines
toward the air gaps between the strips. Stagnant flow regions at the
edges of each strip, revealed through potential flow calculations,
then caused higher liquid imbibition and impaction there for water
harvesting. It was also found that the Cassie nonwetting substrates
that originally exhibited contact angles of 161° transformed
to Wenzel wetting with zero contact angle within 60 min of fog interception.
Optical profilometry revealed no obvious difference in surface roughness
between the central region and edges of the strips, indicating that
surface morphology was unlikely to be a contributing factor for enhanced
water collection at the edges. The findings here indicated that highly
wetting vertical strip architectures with narrow widths (1 mm) were
favorable over wider strips for water harvesting provided that clogging
and re-entrainment were not significant factors.
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