Certification of SRM1960: Nominal 10 μm Diameter Polystyrene Spheres (“Space Beads”)
Experimental, theoretical, and calculational details are presented for the three independent micrometrology techniques used to certify the mean diameter of Standard Reference Materisd 1960, nominal 10 μm diameter polystyrene spheres (“space beads”). The mean diameters determined by the three techniques agreed remarkably well, with all measurements within 0.1% of each other, an unprecedented achievement in the dimensional metrology of microspheres. Center distance finding (CDF), a method based on optical microscopy, gave a value of 9.89 ± 0.04 μm, which was chosen to be the certified mean diameter. The supporting measurements were done using metrology electron microscopy (MEM) and resonance light scattering (RLS). The MEM technique, based on scanning electron microscopy, yielded 9.89±0.06 μm for the mean diameter of the microspheres in vacuum, while the RLS value was 9.90 ±0.03 μm for the microspheres in liquid suspension. The main peak of the diameter distribution for SRM 1960 is nearly Gaussian with a certified standard deviation of 0.09 μm, as determined by CDF. Off the main peak, there are about 1% oversized particles and a negligible amount of undersized particles. The report gives a detailed description of the apparatus, the experimental methods, the data-reduction techniques, and an error analysis for each of the micro-metrology techniques. A distinctive characteristic of this SRM is that it was manufactured in microgravity aboard the NASA space shuttle Challenger and is the first commercial product to be made in space.
The Influence of Physically Doping NaCl with Other Salts on Aerosol and Solion Generation
The paper presents the influence of physically doping NaCl grains with 0.5% KCl, KI, MgCl2 and CaCl2 on the release of negative aerosols/solions in dynamic halochambers. The salts used for doping were chosen according to the current procedures to obtain therapeutic and ambient mediums in aerosols with a negative charge based on NaCl. The aerosols were released by pumping an airflow of 1.8 L/min through a cartridge containing 60g of porous granules, with diameters between 4.0 and 6.6 mm, which were obtained by extruding dispersions of aqueous pasty-damp, saline solutions. We used an optical particle counter and a micro-chamber, divided into 10 equal rooms and with a zigzagged airflow delimited into three areas in each room. The upper side was fitted with several injectors to be coupled to the particle counter. Using this device we studied the aerosol emission dynamics over time, by keeping the temperature and humidity in normal conditions, as in the atmospheric air. Based on the evolution of the saline particles, which were divided into two stable groups in the air, namely gaseous microdispersions and gigantic dispersions, we evaluated their concentrations over time, by keeping the airflow that was pumped into the capsule constant. We thus determined the emission ratio over time and the lifespan of the solions in the three areas, over the halochamber functioning period and after the emission ceased. Aerosol/solion generation involves different sets of laws, based on the nature of the doping salt and the conditions in the environment. Therefore, one may select the doping conditions for the aerosol/solion generation granules and the optimal dynamic halochamber functioning time, for use with preventive, therapeutic, or physical performance enhancing applications.
Cognitive Correlaretes of Physics Achievement of Some Nigeria Senior Secondary Students
Some cognitive correlates of physics achievement of some Nigeria senior secondary students were considered in the study. Specifically, the study examined the relationship between measures of student’s field independency. Cognitive tasks, formal reasoning and their achievement in physics. Purposive and stratified random sampling techniques were employed to obtain a sample of 524 senior secondary two students from six education zones in Kogi State of Nigeria. Three instruments were used. They are science Reasoning Tasks (SRTs). Group Embedded Figures Test (GEFT) and Physics Achievement Test (PAT). Data analysis using multiple regressions reveals that measures of students’ fields’ independency and cognitive tasks predicted student’s achievement in physics generally. However, only measure of field independency predicted students’ achievement in physics in the higher order cognitive demand questions. Measures of formal reasoning had no significant relationship with students’ achievements in physics generally or in higher order cognitive demand questions in physics. However, the overall relationships between measures of field independency, cognitive tasks, formal reasoning and students’ achievement in physics generally and in higher order cognitive demand questions in physics were both significant. Educational implications of these findings were discussed.