Lower Critical Angle Research Articles

Switching Direction of Liquid Flow by Amplification of Wetting Properties of Partilly Roughened Prism Array

Superhydrophilic and superhydrophobic surfaces inspired from nature have been developed for anti-fogging, anti-reflecting, water-repelling, anti-icing and self-cleaning films. The amplification of the hydrophilicity and hydrophobicity originates from surface roughness, particularly from their multiscale geometry. In this paper, we present a strategy to exploit the enhancement of wetting properties on roughened surfaces for switching the direction of unidirectional liquid flow on an opened microchannel. We exploit a unidirectional liquid spreading on a hierarchical two-face prism array, which have the symmetry in microscale while having the asymmetry in nanoscale. Based on the switching the direction of the lower critical angle, the transition of the surface chemistry results in the change of flow directions in an open channel.

Comparison of resistance to sliding between different self-ligating brackets with second-order angulation in the dry and saliva states

Resistance to sliding was investigated for 3 self-ligating brackets having passive slides and 3 self-ligating brackets having active clips. Four of these products are currently marketed, and 2 are of historic interest. For all cases, an 0.018 × 0.025-in stainless steel archwire was drawn through each bracket at a rate of 10 mm/min over a distance of 2.5 mm. For each bracket, the resistances to sliding were measured at 14 second-order angulations, which ranged from −9° to +9°. Both the dry and the wet (human saliva) states were evaluated at 34°C. From dimensional measurements, the critical contact angles for binding were determined for all products and ranged from 3° to 5°. Below each characteristic critical angle, brackets with passive slides exhibited negligible friction; brackets with active clips exhibited frictional forces as great as 50 cN (50 g). Above each critical angle, all brackets had elastic binding forces that increased at similar rates as angulation increased and were independent of bracket design. Generally speaking, at second-order angulations that exceeded the critical angle, brackets with active clips that had a low critical angle had more resistance to sliding than did brackets with active clips that had a higher critical angle. Brackets with passive slides that had a high critical angle exhibited the lowest resistance to sliding, but could do so at a cost of some loss of control. Nonetheless, self-ligating brackets represent a compromise between friction and control; ie, self-ligating brackets produce frictional forces that are more reproducible than do conventionally ligated stainless steel brackets but without the potential control problems associated with Begg-style brackets. (Am J Orthod Dentofacial Orthop 2002;121:472-82)

Performance study of polycapillary optics for hard x rays

In order to investigate the feasibility of using Kumakhov capillary x-ray optics for high energy x-ray applications, measurements have been performed on the behavior of capillary optics from 10 to 80 keV. Transmission efficiencies of straight polycapillary fibers of different types have been measured as a function of source location and x-ray energy. The measurements are analyzed using a geometrical optics simulation program, which includes roughness and waviness effects. Despite the low critical angle for total external reflection at high energies, capillary x-ray optics appear promising for many hard x-ray applications. Transmission measurements at high energies have also proven to be a very sensitive tool in capillary quality analysis.

Response of the CN-85 SSNT detector to low-energy protons and deuterons

It has been reported that the CN-85 detector is able to register only alpha or heavier particles. It was supposed by many scientists that its sensitivity of protons is very low, and that therefore it can be used in conjunction with the CR-39 detector which has a high sensitivity to protons, and thereby discriminates between protons and heavier particles. In this paper we describe our efforts to determine the registration of 1–2 MeV protons and deuterons in chemically etched CN-85 detectors. Samples were etched with 2M NaOH at 70°C. It has been found that CN-85 has a high response to low-energy protons and deuterons. In view of this, and also because of the low critical angle of registration of these particles in CN-85, in any attempts to use CN-85, especially in neutron therapy or neutron dosimetry, these points must be taken into consideration.

Low energy protons and deuterons track registration in CN85 SSNT detector

It was assumed that CN85 registration threshold was alpha particles or it has very low registration efficiency to proton, therefore it has been used together with CR-39 detector, which has high sensitivity to proton, for discrimination of protons in particle mixtures by many of the scientists. In this paper, we describe our efforts to determine the chemical registration of 1 to 2 MeV protons and deuterons in CN85 detectors. It has been found that CN85 has very high response to low energy protons and deuterons. Therefore, due to this fact and because of low critical angle registration of these particles in CN85, in any attempts to use such a detector especially in neutron therapy or neutron dosimetry these points should be taken into consideration.

Spectral Reflectance of Solids for Aluminum K Radiation*

The fraction of aluminum K radiation reflected from flat glass, magnesium, aluminum, copper, silver, and gold surfaces was measured as a function of the angle of grazing incidence. A single vacuum chamber enclosed the 0.01 in. diameter, aluminum wire anode x-ray tube, 15-μ thick absorption filter, CeBr(Tl) scintillator, refrigerated 6199 photomultiplier, reflecting surface, and metal evaporation source. The metallic surfaces were films deposited on glass flats already placed in position for immediate reflectance measurements. A linkage caused the x-ray beam to impinge on a fixed portion of the scintillator to avoid detector nonuniformities, and the photomultiplier-detector was cooled with ice water to reduce thermal noise.Excluding two anomalous cases, the critical angles average 9.3% below theoretical calculated values, and absorption ratios 28.2% above. A reduced material density could account for the low critical angle, but no simple explanation was conceived to account for the absorption discrepancy. Interference extremes produced by reflection from the aluminum film were in agreement with predictions of a revised interference theory.